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Old Aug 24, 2012, 01:17 AM
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HPI RS32 spins out on left turns?!?

On smooth garage concrete made slightly tacky with sprayed on Coke my RS32 spins out easily on left turns even at low speeds, right turns are fine. I didn't notice the issue when running on short carpet. It appears the back end is losing traction and it sounds like the right rear wheel chatters during the slide. Below is a list of notes and things I've tried to rectify the problem, the solution eludes me. I saw a post from someone else that noted 'erratic left turns' so I know this is happening to others too. Has anyone found a slolution or have ideas for a fix?

Notes/solutions tried
1. Broke in the diff by holding one wheel at a time while running forwards and backwards. The diff is really smooth when I turn one wheel at a time, but seems to bind a bit if I put some left/right pressure on the spur gear.

2. Oiled the diff and ball bearings.

3. The front wheels are on ball bearings and both roll freely.

4. Swapped rear left and right tires

5. Swapped rear axle, wheels, gears, tires from a second vehicle

6. Alternately taped a weight (AAA battery) to the front, rear, left and right sides of the car, taping the battery to the rear helped a little, front made it worse, left and right did nothing.

7. To rule out a warped T-bar, a super flexible T-bar was fashioned out of flimsy plastic, it didn't help at all.

8. Tightening the diff helps some, but it can only be tightened so much before the plastic nut strips. I may try locking the diff with gum, playdoh, etc..., or try a nylon nut that won't strip.

9. There is a bit of left/right slop in the rear axle so the rear wheels were carefully positioned to one side to closely track the front wheels. If the axle is moved to the other side the tracking appears to be off by a few millimeters.

10. The motor is upgraded to a coreless Blade mSR so there is very little motor drag which should help keep the back end from breaking lose.

11. The servo travel is smooth both ways and left and right low speed turns are about equal in radius.

12. I've noted that the right rear wheel on these cars is a bit wobbly, I suspect that on left turns the wheel wobble is somehow affecting the diff, but for some reason it doesn't affect the diff on right turns. I only hear the chatter from the rear wheels when the car spins out on left turns. Maybe the wobbly right rear wheel is causing the chatter and spin out?

Fixes I haven't tried.
1. Locking the diff

2. Try to remove the right rear wheel wobble, gluing the right rear wheel to it's gear may help.

3. The diff may be binding on left turns, maybe a shim in the middle of the diff would help

4. A large plastic washer glued to the plastic nut that holds on the right rear wheel may take out some wobble.

5. ???
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Old Aug 24, 2012, 07:20 AM
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Canada, ON, Whitby
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What side of the car is the diff on? Locking the diff will make it want to spin in both directions, so you don't want that.
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Old Aug 24, 2012, 12:10 PM
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If you look at the rear of the car the diff is on the right side.

Another thing I haven't tried is playing around with the preload adjustments for the front suspension. There are some set screws that increase the preload, though it is so stiff to begin with I don't think the suspension gets activated unless a bump is hit.
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Old Aug 25, 2012, 01:22 PM
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could also stem from haveing excess traction on the front like hooking one way more than the other have you tried balancing the car ?? and also check to see if the tires are turning equil in the front from right to left . can also try tweeking the car by adding preload to the oppisite side from wich it is spinning . so you would add preload to the left front to force more traction on the right rear . remember these are similar to turing cars and tuning may be a handful as little changes make a big difference even more so the smaller the scale .
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Old Aug 27, 2012, 01:58 AM
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Quote:
Originally Posted by rcphreak View Post
could also stem from haveing excess traction on the front like hooking one way more than the other have you tried balancing the car ?? and also check to see if the tires are turning equil in the front from right to left . can also try tweeking the car by adding preload to the oppisite side from wich it is spinning . so you would add preload to the left front to force more traction on the right rear . remember these are similar to turing cars and tuning may be a handful as little changes make a big difference even more so the smaller the scale .
I checked the left/right balance, the left side is a little heavier. I'll try adding weight to get it even and retest. On slow turns left and right turning radius is about the same. The front suspension preload was adjusted to full one side at a time, it didn't help. Also the right rear wheel was made less wobbly by super gluing it to it's differential gear and adding a large thin plastic washer just inside the plastic wheel nut. No improvement was seen.
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Old Aug 27, 2012, 05:32 AM
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remember only make one change at a time im confedent youll get it sorted but dont change too much at once or it may end up driving worse . at this small scale a little is a big difference and alot of times it can be combative but when sorted you may in fact hold the key to a proper race setup . and dont make the car too stiff alow it to roll or rather be able to pitch under its own weight ( not you pushing on it ) while driving once you can see it pitch then you have a starting point .
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Old Sep 02, 2012, 09:29 AM
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Are all the bearings in good condition? I have a mini highroller, and it has a similar thing but to a lesser effect. It only shows up on very slick surfaces. I think it was a bad wheel bearing, which was creating drag on one side, so it wanted to slide out in that direction
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Old Sep 02, 2012, 07:31 PM
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i have another question for you did it always have this issue or did it start after you started modding it ???
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Old Sep 04, 2012, 12:51 AM
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Zanek: Both front wheels spin freely but if I'm still hitting a wall I may try swapping wheels and bearings.

rcphreak: I only tested the stock car on carpet and hardwood floor before starting the mods. The car didn't spin out on carpet because there was a lot of traction, and spun out in both directions on the hardwood because it was so slick. I have another stock rs32 that I'll try out in the garage, if that one doesn't spin out I can try mods one at a time to see if it's one of the mods that is causing the issue.

I think the front suspension on this car is too stiff, if I put all the cars weight on a front wheel the suspension hardly budges. It looks like the springs could be replaced by a piece of piano wire which would give more action to the front.

I've been working on a way to bias the rear suspension to one side or the other with a rubber band. Twists are added or removed to adjust the bias. I'm hoping that I can adjust the bias until the steering is neutral.
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Old Sep 04, 2012, 01:46 PM
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What happens if you take the motor out and try rolling it, does it still spin the same? That'll tell you if it's purely suspension, or related to the diff/motor cogging when coasting or under power.
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