Project: Ultimate Street Sport
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This is the story of an underdog among underdogs. Traxxas is not known in this day & age for producing race-ready vehicles, but two of the company's products are particularly embarassing to lay eyes upon. The Spirit, based on the fairly ancient Tom Cat buggy platform, combines Tamiya Grasshopper-era technology with the construction quality of a Radio Shack vehicle. Then there's the Street Sport, arguably the worst-performing truly "hobby-level" on-road R/C in production today.
Just because a vehicle isn't top-of-the-line, though, doesn't mean it can't be given a makeover, souped up nicely, and transformed from an object of shame into a source of pride.
Enter the Ultimate Street Sport.
In case you haven't seen either of my updates on my YouTube channel , here's a quick summary of what's gone on in the past year of on-again, off-again work on this now pathetically ancient project. First, here's the new body:
It's a simple 200mm lola with the driver cut out to make room for the servo. No worries though, I have something clever figured out to do with the hole later. Next up, the wheels & tires:
Yep, duallies. These are GRP nitro rears, 35 shore. They're carefully superglued face to face, but more importantly, they're mounted securely on the most ridiculously long axles you'll ever see on one of these cars. Those stubs are from an old Sledgehammer, and they're perfect for the job! Turns out these crazy-wide foamies are just the ticket! Since I put them on I haven't been able to spin more than 90 degrees under power without it squaring up and regaining control, regardless of the speed. With a quick dose of traction compound, they're good to go anytime I need. You can also see in the pics that I slightly modified my longitudinal links. Previously the allthread actually threaded through the uprights, but now they pass through and are secured by a nut on each side, making them adjustable to help tune the toe-in.
Pretty much anything that could go wrong in testing has, sadly, including multiple instances of strong gusty wind picking up just when I got to my testing lot, a servo locking up for no reason, glitches, and lots more. On my most recent run, I hit myself. In the foot. At an indicated 45mph. Something went crack, and unfortunately it wasn't my foot.
Ouch. Looks like I've got a lot of work ahead of me.
Things were a little slow the past two weeks on the project front, but late this evening I finally got the Street Sport back up & running. I'm now using the new body, a 5-point rear suspension setup, and my most radical tire setup to date, for any of my projects. By the time I got out to the testing range, unfortunately, the sun was already down and the asphalt was cold, so I wasn't able to do any apples-to-apples comparisons with the previous setup. What is certain is that the new tires improve straight-line tracking and off-throttle stability and the body, so far, is not making the car fly away. Once the tires were broken in & warm I was able to hit 100% throttle briefly on one run, but not top speed just yet.
More tests to come this week, I hope.
Went back out to the "spot" today on a clear day with a mild breeze and minimal gusting. When I got there, what did I find? About a dozen other RC'ers! I spend some time chatting it up with all of them and shooting the radar at their cars, mostly 1/8th scale onroads. The slowest was 59mph, and the fastest were 68 on their best runs. After awhile we swapped positions to see what the little electric could do. Again 80% throttle EPA was the highest I could go before I started to encounter problems of spinning out or, worse still, flipping straight back. Still at 80% and never getting to full throttle until I was already passing the radar gun, I recorded a best speed of 60mph. The most memorable run, though, was 59mph sliding by the gun upside down after flipping over! Unfortunately that run was with the body off, and I damaged the capacitors on my speed control pretty badly. It kept running just fine, though, until I managed to strip my spur gear, ending the day.
Alright, that's it, time for dramatic measures -- body #3, and lead weights to keep the nose down!
This evening I took the car out for its first speed tests with a radar gun. I had not recharged the battery from my last full set of runs, but I was mainly itching to get some real data back to get an idea of what range I was working in. At 50% throttle (limited via EPA), the car hit a solid 45mph. As I inched up the EPA, though, I started feeling the battery going flat, and the last run I made was at 80%, hitting a mere 58mph. I'll charge up the battery fully and try some more realistic passes over the coming week.
Alright, this is it, my last-ditch effort to make things work with a normal-ish body. First up was a new aero device to help cancel the lift coming off of the roof of the Enzo. The wing is from an HPI Super Nitro body and significantly trimmed down. What's great about it is that the center is mostly flat & level, while the edges are angled up. I cut off almost all of the rear surface, leaving only a slight curled-up lip to provide a little extra downforce. Clean air coming around the sides of the cabin hits the angled sides to actively provide negative lift. Air coming off the roof hits the flat section of the wing, giving it less distance to fall and thus decreasing the buildup of low pressure. What air gets under the center section of the wing gets an extra upward boost off the molded-in deck spoiler, which lines up with the lip on the wing.
That looked all well & good, but I'm getting quite tired of thinking I've got things figured out, only to discover the next design shortcoming on my very next run. My problem this last time was a lifting rear end at speed. Two things could help solve that, so I wasn't going stop at just one. I decided to move as much weight to the rear of the chassis as possible. Where's the most weight on this thing? The battery of course. However, the pack was already squeezed right up against the front of the transmission, so I had to swing it around perpendicular to the chassis to move it back any further. This required blasting chunks of plastic out of the sides of the chassis channel to mount Associated battery cups on a 2mm graphite skeleton. The missing channel sides left the chassis as flimsy as a wet noodle, so to shore it back up, I created an upper deck using the same 2mm graphite (the same old sheet purchased for the Ultimate Bandit), firmly secured in six spots. I reorganized the electronics, sitting the ESC on the upper deck right against the transmission, to keep the wiring short and away from the receiver. The motor wires were braided to reduce the strength of electromagnetic fields. The receiver, in turn, was moved as far away from the power wiring as possible, and the antenna was routed further forward still. Finally, the trusty old Lehner Basic 5300 was pulled out to go back in another project, and a Castle Creations CM36 5700Kv was swapped in.
The battery relocation moved 1oz. of weight to the rear tires, and the longer motor added yet another ounce. With everything shored up, it was time for my next test.
Back out at the proving grounds, I started with a conservative 50% throttle EPA setting. Much to my surprise, I immediately noticed the increased speed of the higher-kV motor. I was also very delighted that the runs went without incident, and the car seemed planted. At 65%, there was again no incident. Things were looking good, so I went for 75%. On my first run I didn't get up to full speed, so I brought her around for a return run with a better lineup. About halfway down the straight, I squeezed the trigger all the way. A fraction of a second later, the car hit a very small bump and everything went into slow-mo as it got airborne. The nose lifted about 2 inches off the ground, then the rear followed. It began to spin in midair, now about 3" off the ground, gently oscillating like a spinning top. It went 180 degrees. 360. 450. It touched down perpendicular to its direction of travel, but on all 4 tires. It skid for about 10 feet before I got it straightened out and back under control. All of the slots I cut in the body to bleed out air seemingly did their job. The next run was clean, but the next run after that brought another similar spinning flight with an easy landing. At 75% throttle, though, I was very happy with the handling of the car, I just needed more space to handle the speed. Feeling confident overall, I decided to bump the EPA up to 100% to see if I could manage a clean enough run to squeeze the trigger all the way, if even for just a single moment. After a few dry runs, I got what I was looking for, one of my fastest runs yet, with yet another burst of acceleration at the end that proved that this car has a lot more to give than I've seen.
I think I've finally got it, a formula that works! Now I only need to find an even larger space to run in so I can get some real WOT runs in and see about getting some speed data from this little monster.
The new wheels & tires arrived, got one glued up, and voilla, harmonic vibration gone. Back out at the testing grounds, unfortunately there was very gusty wind, not ideal conditions, but you use what you've got. This time, 30% throttle was no sweat. Even 40% worked, though I was getting some instability and occasional spin-outs at speed, which I attributed to the wind. Going up to 50%, it became still more difficult to make clean passes, but it wasn't impossible. One thing I noticed was that above ~30mph, the faster I'd go, especially when driving into the wind, my front splitter would start grazing the ground a bit. This means either there's too much front downforce or I'm still getting lift towards the rear. Just for kicks, I took the body off entirely. Immediately I was able to do several stable 50% throttle passes! Just how comparatively stable the car is with no body both fascinates and worries me. More on that in a second.
With 50% working, I went to 65%, and it started to become difficult again, but I did manage a couple very clean downwind passes. The speed is now starting to make me go cross-eyed. Seriously. I wasn't able to see straight when I stopped watching the car. It's now definitely the fastest RC I've ever had or seen in person. Confidence running high, I decided to give 75% a try. Shouldn't have done that. I need more room for that sort of power, and in my haste to try a fraction of a second at full speed (like I was doing starting at 50%), I stripped the spur. Back to the shop.
Alright, so aero is still an issue. I don't know why I found this surprising; the scale speeds here are surely passing 500mph and the car only weighs 3lbs fully loaded. I'm going to try an external aero device to help cancel the rear-bias lift, and I'll also increase the forward rake of the chassis to hopefully get more of a vacuum under the car. If that doesn't work, it's time to get drastic with the body work.
Body's done! What do you think?
Did I mention this car is all about that top speed? A lot of aerodynamic tricks were employed with this body. The most obvious are the very low mounting and the mostly-closed rear fenders (the crescent cutouts are to account for tire ballooning and the ample suspension travel). More subtly, though, I've made cutouts for the radiator outlets (on what would be a "hood" on a front-engine car), at the base of the windshield, behind the front fenders, and above the rear bumper. All of these should contribute mildly to downforce and reduced drag. Back on the dramatic end of things, the underbody worked out pretty well, including an up-sloped rear section, and I got the front splitter pretty nicely mated up with the body thanks to a whole lot of sanding work.
With the body literally resting on the transmission and the upper front shock mounts, I trimmed the body posts down as flush as possible. All told, this left the car once again ready for the road.
I found a new, smoother large tarmac space to run in, and was delighted to find that the car did not bottom out at all, even with the very low front clip. I started out with the throttle endpoint on my radio set to 50%, but unfortunately this was too much for the surface and I had trouble with traction. Dialing it back to 30%, I was able to get some straight runs in. I didn't take precise measurements, but I've tested the speeds of enough RCs to know that I was hitting 25-30mph. Yes, that's 30% throttle.
When I inched up to 40%, though, I encountered strange steering adjustments as speed went up, and before I got to the full potential of the available speed, the car would suddenly spin out. Back in the workshop, careful inspection revealed that one of my rear wheels is slightly out of round, and between 30% & 40% throttle, a resonance kicked in that effectively made that tire larger in diameter as it rapidly shook. One of the problems here was that the bearing carrier actually had some play in it around the suspension pin, so to correct this, I swapped in some stock Rustler carriers that fit remarkably snug. This helped quite a bit, but an out-of-round wheel is an out-of-round wheel, and beyond 5,000 wheel RPM, it's a serious problem, especially when the car is capable of 15,000 wheel RPM. There's nothing I can do but replace the wheel. I've already got a couple replacements on the way from Tower.
At least the areo didn't feel like a problem at all this time. I wouldn't mind moving some weight rearward, though.
To be continued...
Alright, I got new body mounts set up that allow me to go as low as physically possible (the rear deck will actually rub on the top of the transmission). After doing some fine trimming on the underbody, I was able to start forming that nice venturi chamber I've been planning for. The only problem is, the body sits so low that my 26mm tires were too wide for the Enzo front fenders.
Okay, no problem. I had some Kawada 21mm racing slicks just waiting for a project to use them on. By skipping the inner bead on the wheels, I was able to test-mount these skinny tires perfectly. That let me mount my body still lower in the front. However, the next limitation I discovered is the diameter of these touring car tires. If you look carefully in the middle picture below (click it to enlarge it, of course), you will see two narrow strips that look like wet or oily patches on the tires and/or body. Those are actually contact patches between the soft racing slicks and the body. Yep, that's hard-core rubbing right there. Given that I'm running soft suspension to help with negotiating surface irregularities at high speed, I'm going to need a lot of wiggle room under those fenders, yet I still want to angle my body down further in the front. I want to get it as low as possible, to where the front shock tower is nearly touching the underside of the front bonnet. Time for new wheels & tires.
Desperate to preserve the bearing-in-wheel setup native to this car, I tried a set of Mini-T wheels. These fit, sort of. I know I can get Mini-T slicks, but those would probably balloon quite a bit. I could use foams, but those create a harsher ride. Also, Mini-T wheels require a good deal of spacing and would probably require some trimming on the spindle arms to avoid rubbing. All in all, not the best solution. Kinda looked cool though.
Alas, I'm out of options. I've got to switch to hex hubs up front to open up new possibilities. Fortunately it's a no-sweat process involving swapping in Dremel-trimmed Rustler carriers like so:
I also trimmed down a pair of hex adapters to be thinner than usual to help make up for some extra width that the new setup adds. To fit these new mounting points, I have ordered a set of HPI Mini wheels & belted x-pattern radials (to match the rears). This will give me a much smaller diameter, smaller even than the Mini-T setup, so I should finally be in the clear. It is likely, however, that I will need to remove my graphite spacer blocks from under the front bulkhead to essentially raise the chassis again with respect to the front axles. This will allow me to maintain sufficient ground clearance up front to handle medium-rough tarmac surfaces.
And now I wait for a package to arrive in the mail from Tower...
Mmm. Body. Hot body... and an underbody too. Staying with the top-of-the-line Ferrari theme, the new shell is, obviously, an Enzo. I had wanted to do an FXX, but when I bought this one Tamiya was only selling the prepainted FXX body. Now the clear one is out and I'm a little mad. Ah, well, can't win 'em all.
As you can see, the underbody-under-construction is perfectly flat at the moment. I will actually curve the rear up just a tad when it's done. Also, don't forget that the entire chassis is going to slant up towards the rear when the tires are mounted, to create that nice vacuum effect. The body, however, will remain at the same angle you see in the photos -- only the chassis will be raised relative to the ground. This will give some room for the sides of the body to form skirts to enhance the vacuum-trapping properties of the whole assembly.
The pronounced front splitter is made of thick 0.060" Lexan, the same stuff most 1/8th scale monster truck shells are formed of these days. This should help keep air going where I want it to go while maintaining some level of survivability on the decidedly imperfect surfaces I have to drive on.
Finally I received a new body, so finally I can proceed! All sorts of thoughts started circling through my mind rapidly the first time I laid the new shell over the chassis. I ended up going with a "190mm" body that's 195mm at the rear axle. To fit the rear wheels under closed wells, I ended up having to, get this, narrow the track again. I only needed 2-3mm, so the 4-Tec arms stayed on and I just switched to slightly thinner drive hexes. At the front, I only had to flip my wheels back around to their normal orientation.
To get my planned underbody to work well for aerodynamic downforce, I realized I would need to slant the chassis up slightly from front to back as there's not enough room on the sides to create proper Venturi tunnels. Out came the spacers I had put under the transmission back in March of '04, and up raised the rear of the chassis by 4mm. Now, that didn't make me all too happy as it raised the average CG of the battery, ESC and receiver by about 3mm, too. Fortunately the standard battery is light (thank you LiPo), but raised weight is raised weight. To make up for my wrongdoing, I immediately replaced four steel screws that were used above the height of the battery with aluminum ones. Then off came the entire rear shock tower, and the shocks were re-mounted to the tabs on the transmission, just above the camber links, thus laying down the shock angle quite a bit. I realize I will have to add back something for rear body mounts, but I'm confident that I can do something more spartan than the original setup. For now, the scale tells me I have removed a full ounce of high-mounted miscellany. I feel better. I'm also going to be able to mount the body lower than expected at the rear, thanks to the demise of that shock tower.
Of course, the biggest improvement from all of this comes from the fact that I'm turning the entire underside of the chassis into a giant aerodynamic device, obviating the need for a rear wing. Yes, the trick variable-pitch setup is being decomissioned, along with the drag-inducing aerofoil, spring steel uprights, heavy body reinforcements, and high-mounted servo. The weight and CG improvement from this switch is quite significant.
Oh, one other important thing the additional chassis height in the back provides is ground clearance. Running soft suspension for traction over asphalt, I was getting too much bottoming-out and scratching the rear underside of the chassis and especially the low ESC platform. No more!
So, what is this fantom new body I've picked up that allows for all of these great changes? Nah, I won't share that just yet; just wait for photos once I get it painted up & mounted! I will say one thing, though. Given what I started with, most people should agree that the new shell is an appropriate upgrade.
In the photo at the top of the page, the rear tires clearly come right out to the edge of the 190mm Hot Bodies Ferarri F-50 shell. That was all well & good with the oversized Super Nitro set, but now that I'm back to more moderate-sized 26mm wheels, I've found myself having to settle for barely more than the Street Sport's original width -- 185mm to be exact. Up front, with my stock wheels inverted, I have a very nice 196mm, but the front isn't where I've been having trouble for weeks. Well, let's hear three cheers for inspiration:
Looks normal, right? Indeed. The only difference is, those are electric 4-Tec a-arms, 4-Tec steering links for camber links, and Nitro 4-Tec slider shafts on the stock outdrives & stub axles. All of these parts are from the scrap pile left over from the 4-Tec rally conversion and TRX-4. The result? That'll be +5mm per side, thanks much! Now she's even between the front & rear at last, so I should have much better stability under acceleration. Since I'm going to create an underbody, I have decided to shop for a new body first. With the new added width, I will step up to 200mm shells and hopefully be able to keep the rear wheel wells closed.
At this time, just for kicks, I'd like to take a very brief trip down memory lane to look once more at how it all began and contrast it with the most recent full photo of the car:
After I looked at how much work would be needed to fully transfer the motor system over to the Mini-T, I decided to hold off on that and just wait until I could get new tires for the Street Sport to continue with its testing. Well, the tires came in yesterday (ahead of plan), and I went for another test run today. This time, to aid traction and help get the power under control, I simply ran with a 6-cell NiMH pack. With this, I was able to set my EPA back to 100% and reset my controller for linear power delivery, though I kept starting power and timing low. It worked! I was able to hit full throttle on almost every pass. I did some experimenting with the wing angle and actually found that I got the most stability at a ridiculously steep angle, somewhere around 40 degrees by my estimation. When I flipped it down to its nearly flat position, bumps in the road would unsettle the car noticeably more and it was much harder to control.
I was able to see even more how aerodynamics matter when a small gust of wind came along out of nowhere and the car went for another 5 aerial rolls with 3 brief touchdowns along the way. I think it's now time for me to get even more serious about airflow and start looking at sealing up the underside of the car.
I've now switched to cut-down ultra-soft Losi 1.6lb/in springs on the rear (which needed to be preloaded quite a bit) and swapped in some 40wt oil in place of the old 70wt. With new hex adapters in place, I clamped each GRP wheel on with an inside-out HPI aluminum wheel spacer, which fits perfectly over a tiny bit of unthreaded axle that pokes through, and settles into the indentation in the outside center of the wheel.
In testing, I found that these give me enough traction to run on unsealed asphalt, but not the sealed stuff. Now I have a new problem: Drift. Not the Fast & Furious 3 sort of drift, but the whole car turning slightly and inexplicably to one side or another at speed. A 1 1/2-second tire scrub over a painted stripe in the parking lot I was at melted right through the stripe, and also showed me that my the foams are not perfectly true. Examination of the front tires revealed that one is looking alright, but the other has a distinct side bias in addition to a wobble. Add to these the very typical-of-Traxxas play in all the joints of the car, and I think I have a good explanation for my drifting problem. What's interesting is I didn't notice any problem when I was running all rubber tires. Factor in the better traction I got with the rubber tires and I think I'm ready for those HPI belted radials about now, probably 4 of 'em. However, unfortunately there's not enough left in my RC budget for this month, so I think I'll be transferring the motor back over to my Mini-T project for awhile.
Success! Well, sort of.
I went to a larger, more open lot today, armed with two new sets of tires. The first are GRP 30mm wide foams in fairly soft 35 shore. These gave me much more traction than the Kyosho SuperTen slicks, and I was actually able to get from one end to the other without spinning out at around 50% throttle. However, the ride was very, very bumpy over the asphalt. I will definitely need to soften up my rear suspension significantly to run foams effectively. It was a big step in the right direction, though.
Next I put on a set of Tamiya TGX treaded rubber tires, which are just over 34mm wide when unmounted. I mounted mine on 26mm wheels which, quite coincidentally, reduced the effective contact patch to just over 26mm. This high-profile setup gave absolutely amazing forward traction. and enough shock absorption to keep the rear end completely planted. I was actually able to hit full throttle on two of my passes! That's full throttle, with 75% thottle EPA, minimum motor timing, maximum current limiting, for about 1/2 second, after about a 100ft run-up. Heh.
After babying the car around for awhile and only rolling it twice (the first time flipping 3x before touching the ground, the second time either 4 or 5 in the air, but both times landing on its wheels), I decided to test the forward traction of these tires. The result...
Both sides are like that. Yes, the black stuff is melted hex adapter. The good thing is that the wheels stripped before the diff did, so I think I'm going to be alright drivetrain-wise. I also noticed paint on the tires, which got me to notice that ballooning was a problem.
So, next up, softer suspension it will be, with the foams again. If that doesn't give me the traction that the TGX tires did, I will try a set of HPI's X-Pattern belted (to combat ballooning) radial tires in standard touring car size.
Well, a few days ago I took the car out for some serious testing. Fortunately the damage is minor and only cosmetic. The speed is quite ludicrous. However, getting up to speed is a problem. The power-to-weight ratio is so ridiculous that traction is an extremely serious problem. With all of the Mamba Max's settings at their lowest and a very cautious power curve dialed in, I still had to set my throttle exponential down to 60% for it to be driveable. I could get the car to instantaneously spin out from what looked like about 30mph (around 1/2 throttle) by giving just the slightest blip of the trigger. I did observe noticeably more traction at speed with the wing in its "up" position, though, so at least that's working well.
Testing was done on 110 degree F sealed asphalt with soft Kyosho tires. Dust appeared to be the biggest problem. Time to shop for some new wheel/tire combos to try.
Now here's an update a lot of folks have been waiting for. The motor, speed controller, and battery are in!
The new Castle Creations Mamba Max controller is paired with my trusty Lehner Basic 5300kV motor first used in XXX-Tyrannus and now shared with my Mini-T project. The true source of the power, however, is a discreet black cube from MaxAmps holding together three 4000mAh LiPo cells wired in series to provide 11.1V. With only minor trimming to accommodate the cell balancing tap, that 6-cell battery tray now holds the approximate power equivalent of ten of the latest 4200mAh cells, but with a fraction of the weight.
The Mamba Max controller was too big to fit in the tiny right electronics wing of the chassis, but instead of just extending it, I trimmed off the whole side and installed a custom deck made out of Dragon Plate (CF over high quality plywood) mounted absolutely flush with the bottom of the chassis. I figured since I had to do something from scratch, I might as well make it improve performance (lower CG) and looks. The receiver & switch leads are routed under a very small Lexan plate glued to the top of a new CF rear battery hold-down. The switch is then mounted low in the left electronics pod. Just a little bit of Dremel drum sanding allowed my Airtronics FM receiver to squeeze into place after the stock receiver mounts (which actually accomodate the Traxxas receiver on its side) were Dremelled off.
Have I run it yet? Only very, very briefly, as mentioned in this thread on the forums. What I need to do now is update my laptop to the latest version of the Castle Link software and take it and a box of pinions out to a very large, smooth, open space to do some extensive testing & tuning. I want to squeeze as much out of this crazy little car as I possibly can!
Another year (and five months), another update. This time I've actually been doing some work off & on with the Street Sport, I just didn't find any of it interesting or complete enough to warrant a post. Today, though, things really started coming together.
First off, the front end is now pretty complete. I fashioned up a carbon fiber front shock tower brace that really tightens things up. This completely changes the spring rate, as the stock tower was flexing massively under any load. The installed servo is a Futaba standard, just because that's what I had handy and functional. I've also put together some adjustable camber links to combat the excessive stock negative camber in turns (caused by excessive caster angle, actually). At the rear, I finally filled the old gap under the forward upper transmission mount with a piece of trimmed-down Delrin.
Now for the fun stuff! A wing at last! Not just any wing, though. This one is a vintage Team CRP #6001 "Aero Tech" tri-level true aerofoil wing, minus the upper two levels. It came as a kit with a plastic skeleton that you cover with heat shrink. The stock heat shrink is a thin yellow and I didn't like it, so I got some black stuff from a local electronics superstore. It's supported by thick music wire and activated by a Hitec HS-55 sub-micro servo. The sevo is taped to a piece of 1/16" CF-covered DragonPlate scrap from the Mini-Giant: Evolution project. This is Shoe-Goo'd onto thin CF strips that are used to stiffen up the thin rear deck of the body. The stock servo horn is used, trimmed & drilled to fit a Dubro "mini EZ-connector."
The result? See for yourself in this brief video:
It's controlled by the 3rd channel switch on my MX-3. So here's what the car looks like overall now:
At this point I'm just waiting for a new speed controller before putting in the motor and wiring everything up for a test run. Is the end in sight?
That it has been a year since I last gave an update on this project absolutely blows my mind. It hasn't felt like even a small fraction of that time has passed.
At any rate, last night after staring at the chassis every few days for a month, I decided to go to the next level with the whole lowering idea. It's now down to a ride height of about 5.5mm, a far cry from the practically offroad-worthy stance it had before (see the previous update). This time I simply lowered the suspension settings instead of the whole chassis.
At the rear, I fashioned a new body mount tower out of 2mm graphite scrap left over from the Ultimate Bandit. The new piece would serve as a shock tower, allowing me to move the upper shock mounts up about 7mm to lower the ride height and also out about 6mm to lessen the progressiveness and slightly stiffen the effective spring rate. While I had the rear shocks off, I got rid of the stock 30wt oil and went with 80wt to take away the excessive springiness that the stock vehicle is set up with.
Up front, taking advantage of the fact that the car has a very strong rear weight bias, I went to lighter springs, the very same cut pieces of Losi 2lb/in yellow offroad truck rears that first showed up on the Phase II Spyder four years ago. While I was tweaking things up front, I went to 50wt shock oil.
Now, in my last update I mentioned that there was a problem with the steering linkages after I raised the whole front bulkhead & suspension in relation to the chassis and servo mount. Well, my latest changes only made things worse. Fortunately, though, all I had to do to fix the problem was to move the outer mounting points under the steering knuckles (in stock form they're on top).
What's next? First I need to reattach the upper transmission mount that hooks into the rear bulkhead section of the battery tray. Then I'll have to come up with a superior-to-stock method of mounting the electronics (I really don't want to lay them on their sides if I can help it). After that, I believe I'll just pick a good motor, install a servo, wire everything up, and finally get to the truly unique and exciting modification that I've been looking forward to since the inception of the project!
Today I turned my attention back towards the chassis. I had considered doing a full carbon fiber lower deck and perhaps either a center I-beam or a full-length upper deck, but I decided to keep costs down & stick to the spirit of the original vehicle. One thing that I really don't like about the stock chassis, though, is not how much it weighs, but how high it sits off the ground. Even with no shock preload spacers, it had as much ground clearance as a rally car or some off-road buggies. To lower the suspension (raise the wheels) would have been pretty easy in the back with the help of a couple of small extension plates on the inner shock mounts. Mounting the shocks higher would have allowed the whole car to drop down. However, I'd then have to rework the suspension geometry to bring it back into proper form. Up front, the complexities would have been even worse thanks to the odd two-piece bulkhead/suspension mount/shock tower assembly that fits together like two pieces of a puzzle (and uses no fasteners between the parts).
Unfazed, I applied a Photoshop trick. Yes, you read that right. Oftentimes on the Internet you'll see a digitally altered photograph of, say, a car, made to look lowered, with bigger wheels, different color, etc. To get the effect of lowering the car in the picture without making obvious seams around the background where the car once was, photo reworkers often raise the ground instead of lowering the car. On my Street Sport, I did a similar thing. I raised the front bulkheads (along with the entire front suspension assembly) and the transmission (along with the entire rear suspension assembly), which had the effect of lowering the entire chassis:
Much better! At the front I used two Dremelled-up scraps of 2mm graphite, glued in a sandwich, and cut out a notch of material from the bulkhead to match. At the rear, I again used graphite scraps, but didn't have to do any modifications to the stock parts. I just need to make a spacer or two to fill the gap between the forward tab on the transmission housing and the battery tray walls that they should be bolted down to (see the "After" pic above).
The entire main chassis is now lowered by 4mm, with stock suspension. The one thing I did not deal with is the way the steering linkages are now raised in relation to the servo mount, but I was going to have to do something about the primitive, binding, shameful stock steering setup anyhow.
I managed to clean up the wounds a bit and get the painting complete. I actually did end up trying a bit of modelling putty before the black paint. Squadron's White Putty actually sticks to Lexan pretty well. It'll crack on impact, but I plan to avoid any such unpleasantries!
So much for having "another update in less than 3 months!" Ah well, ya gotta take what you can get. Today I completed the construction of the front winglets/venturi tubes, sealing off the seams with Shoe Goo. I've filled & smoothed any gaps as much as possible, but I really need some sort of putty to do it right. Unfortunately I know of no putty that will stick to Lexan, so I'm going to paint the ducts black to minimize the appearances of the blemishes.
In bigger news, I've traced out a chassis design on the remainder of the sheet of carbon fiber that was used to make the Ultimate Bandit's lower deck! Talk about a nice accent for the little CF forward upper deck ;)
It's extremely hard for me to accept the fact that three months have passed since I last touched this project, but I guess that just shows how busy I've been this summer.
In today's work, I started introducing some advanced materials to this fairly primitive vehicle. I made a 2mm carbon fiber forward upper deck, which is about 300% stiffer than the stock unit. Due to the design of the chassis, with the front bulkhead bolted to the chassis, but not braced against the upper dech at all, the extra stiffness won't help the rigidity of the chassis, but it will help the vehicle to steer more consistently by keeping the servo more secure. Plus, ya gotta admit, carbon fiber always looks great. I also made a CF front battery hold-down bar, and plan to do one for the rear as well. Aluminum hardware helps to add to the "pro" look. I've actually considered making an all-CF chassis, but in the interest of keeping costs down, I'll go the Dremel & brace route instead.
The more exciting new developments revolve around the bodywork. Now, normally, a body is just a body. You get it, you paint it, you mount it, and it either looks good or it doesn't. I'm going a LOT deeper than that with my SS. I won't yet reveal my plans for the back end, but progress on the front has begun. To maximize downforce, I'm doing a front wing setup. No, I'm not mounting a wing onto the front of the body, but rather, I'm building it into the body itself, the way the full-scale F50 and countless other top-end sportscars do. This involves trimming out the faux front air inlet, opening up the front upper air ducts, and carefully shaping and inserting strips of Lexan to connect the two. The pictures below show how far I've gotten so far.
Once the Shoe Goo I'm using as adhesive dries, I'll go back and trim the undersides of the new aero-duct walls and install curved horizontal plates fron the underside. When it's all done and trimmed, I'll be left with a pair of sealed tunnels for air to pass through, each with a wing on top, molded directly into the bodylines. This should help to reduce "push" in high-speed turns by measurably increasing front al downforce. Hopefully I'll have another update in less than 3 months.
Finally I got a chance to trim up my new body, a 190mm Ferrari F-50 GTP-style shell by Hot Bodies. I like the aerodynamics on this shell and plan to build upon them. I put the stock wing in the pictures just to complete the look. I'll actually be building a custom active variable pitch aerofoil system before the project is over.
I dropped some sealed bearings in the rear carriers and diff outputs to free up the drivetrain a bit. I then slipped on a set of Rustler/Stampede/4-TEC hexes and installed some HPI Super Nitro black mesh wheels with soft compound slicks. They're about 1/4" larger in diameter than standard 1/10th scale sedan rims, giving an aggressive look and large contact patch that will hopefully help on the traction end as well.
Up front, I wanted to switch to some nicer wheels, but couldn't figure out a way to do so without increasing rolling resistance. I ended up giving in and just threw some bearings into the stock wheels after removing the unnecessary weight of the chrome faceplates. I'm contemplating Dremelling out the front wheels to reduce a tiny bit of rotating mass, but also more importantly, improve upon the looks. The only good unmounted sedan tires I had handy were some Yokomo soft-compound 24mm racing tires called Sprints, so I glued these on gingerly with some medium inserts. To get a perfect fit, though, you want to use 26mm tires. Once these Sprints wear out, I'll likely get some HPI #4435 26mm racing slicks.
I've had the base vehicle for this project for some time now, so I thought I'd at least post up a good look at the stock chassis for folks who haven't seen this remarkably low-tech vehicle before.
|The RTR SS chassis
(click to enlarge)
It's a direct-drive car -- the pinion on the motor drives the diff gear and thus the rear axle without any reduction gears in between. Diff balls are embedded directly in the main gear (which theoretically could be called a spur). Up front, there is no bellcrank steering. A servo is meant to be mounted spline down with a small servo saver, and the steering links connect directly.
The rear uses the same style of outdrive as Rustlers & 4-TECs, minus the hex hub; the axle pin fits directly into a slot that's molded into the stock rear wheels. Up front, on the other hand, static steering spindles are used and 5x8 bushings are placed in the wheels themselves, basically a scaled down version of a Nitro Rustler carrier setup (also used by Losi, Associated, & most other 2WD vehicle manufacturers). The problem with the front setup is that it precludes the use of standard sedan wheels, which have hex inserts. To get around this, you can follow the SS Wheel Conversion Guide contributed to the site by Colin Doyle. I have something different in mind.