Rover tips left when accelerating and right when reversing

[SmarmyNarwhal]

This is a fun when. I put a rover on Duna after extensively testing it on Kerbin but something is off. When I start accelerating I tip to the left. I have pictures but they are subtle so you might have to squint. Here is my rover at rest:

When I push forward this is what happens. The wheels spin as expected, then the springs extend on the right side and contract on the left side, causing the right side to start tipping off the ground:

When I try to reverse the opposite happens. The left side extends and the right side contracts causing the left side to tip upwards:

As a result of this I tip my rover over if I try to move even a little bit. I can't break at all because if I push hard enough to slow down then it flips.

I think what happened is that my symmetry got broken when I put it on the rocket. I noticed the mirror symmetry started pairing things front and back instead of left to right . This means it may think the left side is the front and the right side is back. This would make sense because you would expect the front of the vehicle to tip down on acceleration to maintain friction. I could go back to the VAB and try to fix it but I would have to revert my mission. I'm wondering if there is anything I can do with wheel settings to fix it or if I'm just out of luck and have to restart.

[bewing]

No, it's probably not the symmetry, it's almost certainly a reaction wheel somewhere on the craft generating torque.

In the default setting, the reaction wheels and the rover wheels use the same keys. For the rover wheels, the keys mean "forward, reverse, turn left, turn right". And for the reaction wheels, the keys mean "tilt forward, tilt back, tilt left, and tilt right." So whenever you push a key to try to make your rover go in some direction, it also tilts at the same time.

The easiest thing to do is to go into your settings, and remap the rover controls. You can use the keypad, or the arrow keys, or anything -- just as long as they are not mapped to the same keys as your reaction wheels.

[SmarmyNarwhal]

41 minutes ago, bewing said:

No, it's probably not the symmetry, it's almost certainly a reaction wheel somewhere on the craft generating torque.

Yes and no. I think you are right about the reaction wheel but it is also a symmetry issue, or rather a directional issue. Because I rotated the rover while placing it in the rocket, it thinks the left side of the rover is the front of the craft. As a result, when I push forward, the reaction wheels tilt it left instead of forward. I rotated it back to fix the orientation and did a test run on Kerbin. It worked normally. In the proper orientation there shouldn't be any issue with a little tilt from the reaction wheels, since it may actually help a bit with balance.

[Wobbly Av8r]

Not sure it will help, but under the PAW menu item [for the Probodobodyn Rovemate, if that is what you used, just above] "Control from here" there should be a few options to change orientation of the probe - maybe you can utilize that? [Control Direction: Up, Forward or Reverse]

Edited October 31, 2020 by Wobbly Av8r
Clarifying the Rovemate and options

[Wobbly Av8r]

After a closer examination, it does appear that you have a Rovemate mounted sideways - you'll probably have to turn off the reaction wheels when you are driving to maintain controllability as the control options are Forward (as they currently are) Reverse (which will just cause them to veer right instead of left) or Top, which *might* work as at least the reaction wheels will not be veering left or right, but who knows?

Since you said it tested okay in Kerbin's gravity, you should be able to get the job done without abandoning it...

Edited October 31, 2020 by Wobbly Av8r

[bewing]

10 hours ago, SmarmyNarwhal said:

In the proper orientation there shouldn't be any issue with a little tilt from the reaction wheels, since it may actually help a bit with balance.

The issue will be that reaction wheels use up an immense amount of electricity, and your rover will be drained after going a few hundred meters. On rovers, you really only want to use the reaction wheels in an emergency (your rover is flipping through the vacuum, and you need it to land back on its wheels).

[SmarmyNarwhal]

11 hours ago, Wobbly Av8r said:

After a closer examination, it does appear that you have a Rovemate mounted sideways

I actually didn't use a Rovemate core for this rover. I used something a little bigger mounted underneath. The orientation of it was correct. I was able to rotate the entire rover in the rocket and fix the problem on a relaunch.

 

4 hours ago, bewing said:

The issue will be that reaction wheels use up an immense amount of electricity, and your rover will be drained after going a few hundred meters. On rovers, you really only want to use the reaction wheels in an emergency (your rover is flipping through the vacuum, and you need it to land back on its wheels).

I didn't find I had a lot of electricity issues, but it was a little screwy for the stability. I set the reaction wheel to SAS only and turned of SAS. That worked well enough. I turn it back on if I can flipped over onto my rollcage of landing struts and need a little extra oomph to flip over again. It drives like a dream now as long as I take it easy on the hills on Duna. If I redesigned the rover I would actually put a solar panel on the underside to prevent it from dying while trying to flip over, but otherwise I'm very pleased with it now. I just have to get a scientist out the to drive it!