DEX210: On-power understeer, off-power oversteer

[Origineelreclamebord]

Hi everyone,

I'll be racing my DEX210 on sunday at the Model Indoor Oss (MIO) track in the Netherlands. I've put my car on a basic setup for carpet.

I don't really have the time to go training tomorrow, but I don't want to come to the track unprepared. I found a small patch of carpet locally to test the car. I'm happy with the fact the car doesn't grip roll at medium speeds and agressive turn-in, but there are however some things to work on.

For starters, the car has horrible on-power understeer - all front bite just disappears under high throttle rates. The other thing is that the car feels hugely agressive off-power: the rear end is only just hanging in there and is on the verge of sliding.

The two contrasts are a bit of a problem: cancelling one out may well make the other one worse.

This is my setup:



My theories:
1. The increased rear droop is causing the off-power instability.
2. I should try running pins on the front.
3. I need to try 25 or 20 deg. caster.
3. I need to lose the front toe-out.
4. The 24g behind the battery can be removed.
5. Loosening the slipper might help.

The place where I ran the can today will be closed tomorrow. What are your thoughts on the required changes?

[mrspeedy]

Its always difficult to say for sure, but the Dboots up front and not your best friend ... they're way too grabby and could certainly be part of the off power oversteer, Schumacher cut staggers are good and easy on carpet.

.. .. and the on power under steer might be a result of you having to firm up the front trying to stop the off power oversteer ..

Have a look at the Craig Collinson std setup .. I've found it to be a brilliant starting point

[Origineelreclamebord]

Update: I went back with some tools to try out a few things. The resulting setup can be seen below.



The things I tried and kept:
- 25 Deg. caster: Increased steering (but also made the rear end yet slightly looser off-power), more importantly it made the car feel much smoother.
- 3 Deg. anti-squat: Seemed to add a little on-power steering.
- Rear shock more upright (middle top hole): More initial on-power steering, rear end can be kicked out to make a tighter initial turn. Rear however starts gripping again once the car starts rolling, ending up with (nearly) the same on-power understeer in long turns under power.
- Looser slipper: Made the car less edgy, but didn't add steering.
- Reducing rear droop back to kit level: This did a lot! Off-power the car became calm and stable, on-power the car had better steering in general, high throttle was less affected though than medium throttle.
- Longer front link: The car seemed to get slightly more steering in general, but off-power stability was kept.
- Swapping 24g battery stopper from rear to front end: Increase in steering on- and off-power, front end is more planted, the rear end is visibly slightly looser but in a controllable way.
- Front rollcenter, 1mm lower inside ball stud: The car seemed to have slightly more steering and have a smaller turning radius, yet didn't feel more agressive.

Things I tried but reverted:
- Schumacher Minipins, Yellow (4WD front & wide rear): The car became quite vicious with the car sliding out off-power. On-power steering was good for medium throttle, but understeer came back at high throttle levels. I reverted back to the dBoots setup (as I didn't have cut staggers with me).
- Rear rollcenter, 2mm higher inside ball stud: The car became slightly looser at the rear, helping steering, but I reverted this because I'm afraid the rear end may become loose on the low grip (PVC and Wood) sections of the track.

This is as much as I could have tested on a patch of carpet that was about only 4x8 metres The rest I'll probably have to find out on Sunday. The car feels better already: The off-power oversteer is not there anymore unless you decide to brake into the corner The on-power understeer is still there at higher speeds but is now manageable.

So despite the steps, I bet there's further improvements to make. If anyone has suggestions what could further reduce on-power understeer, your suggestions are more than welcome!

[Origineelreclamebord]

PS: I didn't see your post mrspeedy (I was busy typing) I know the dBoots Blockpass are not the most beloved tire - at the EOS last year, people either used those on 4WD rims and put glue on the outer sidewall of the tire to make the tire calmer (like I did) or used 2WD front nanobytes glued on 4WD rims and cut off the inside and outside 2 rows.

It's a shame I forgot to take cut staggers with me, those combined with minipins on the rear is probably the way to go - I'll find that out on Sunday

[Chris Doughty]

Looks like you have too much rear toe-in and also your shorty pack too far back.

the shorty pack position changing the way the car behaves A LOT!
the further backwards you get the more turn-in and rotation you get in the corner. and the car squares up really well on power (no on-power steering)
the further forwards you go the less initial steering and more on-power steering you get.
Oh, just noticed your ESC is in front... I'm not a fan of this location for the ESC because it limits battery placement.
I have found that battery placement and weight distribution is HUGE, especially when it comes to on power steering and turn-in

Gear diff will also help here too.

[Cody227]

you are experiencing a basic problem.in the design of mm buggies: too much weight transfer. for.some it fits the driving style ver well and for some it doesnt. try using only one idler gear but you will have to change your setup dramatically or else you will have way too much steering in all situations.

[Origineelreclamebord]

Thanks for the comments guys, I really appreciate your help! This will be my first time with the 210 on a track with this much grip. Usually I drive on my DEX210 on dusty clay, sand and medium bite astroturf - that's why the battery is completely in the back. That, and my ESC is so big it doesn't fit anywhere else!

I have an idea though: I could make a lexan sheet with the length of a stick pack. On that I could fit the ESC and a battery stopper. I can then swap this around so the battery is either fitted at the front or the back.

Would this be too extreme a change in weight balance (In other words, am I better off chucking some weight under the servo?) or is it worth a shot?

[Dino_D]

Originally Posted by Cody227

you are experiencing a basic problem.in the design of mm buggies: too much weight transfer. for.some it fits the driving style ver well and for some it doesnt. try using only one idler gear but you will have to change your setup dramatically or else you will have way too much steering in all situations.

Try thickening the rear oil weight. It seems too light. If the front is heavy at 500cst (37.5wt), and the back is 250cst (20wt) what happens is the front doesn't lean or roll and develops a push, while the back leans too much thus the imbalance will cause the car to hook or spin mid corner, or a handful to drive out of the corner. Normally you need to try to ensure the roll rate of the front and rear is close otherwise you will have a ill handling car.. Or unless you got a point and shoot track. straight 180 turn, straight. 90 turn, etc..


Try 30wt approx 400cst front and 27wt approx 350cst rear. Using 1.5x3 holes front and rear. Its a good starting point for a med bite carpet setup.

Also battery placement. The more rearwards you put the weight, the more the car wants to rotate and swing in a corner. Moving it more forward, stops the rotation.