Society of Robots - Robot Forum

Mechanics and Construction => Mechanics and Construction => Topic started by: lanamor on October 17, 2011, 07:40:28 AM

Title: Wheel rudder
Post by: lanamor on October 17, 2011, 07:40:28 AM
Anyone had any experience with differential drive and a wheel rudder (swivel wheel) in the back? My problem is that the wheel rudder always pulls the chassis either left or right. I've centered the wheel rudder and ensured there is no resistance to swiveling.

Just wondering if anyone else has any experience.
Title: Re: Wheel rudder
Post by: Soeren on October 17, 2011, 01:04:08 PM
Hi,

You probably have too much weight on the caster (which likely aren't optimally angled).
Title: Re: Wheel rudder
Post by: waltr on October 17, 2011, 05:33:16 PM
Is the wheel directly under the pivot? Or does it trail behind the pivot?
Go to the hardware store (or search on-line) and look at casters noting where the wheel's axial is relative the the caster's pivot.
Title: Re: Wheel rudder
Post by: lanamor on October 17, 2011, 07:11:22 PM
Is the wheel directly under the pivot? Or does it trail behind the pivot?
Go to the hardware store (or search on-line) and look at casters noting where the wheel's axial is relative the the caster's pivot.

The wheel trails the caster's pivot.

I tried placing less weight on the caster but it didn't seem to help. I also installed a larger caster but the drifting behavior still remained. I installed a ball caster and this seemed to work much better but there is still a little drift to one side. I assume the drift is due to one motor turning very slightly faster that the other. The slight drift I can fix with code but I wonder if this might have been the root cause of the original caster's problem.

If there are any other suggestions or experience I'd still welcome it. I hate leaving problems unsolved!
Title: Re: Wheel rudder
Post by: waltr on October 17, 2011, 07:34:03 PM
If you do not have speed feed-back then the drift is due to one wheel/motor turning faster than the other. Even with identical motors/drivers there will be slight differences in speed.