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[DPRG] Odometry and backlash

Subject: [DPRG] Odometry and backlash
From: Rud Merriam rudmerriam at gmail.com
Date: Sun Jan 4 20:12:30 CST 2015

Odometry is always chancy. Using it to measure instantaneous speed is 
useful. Measuring distance is almost not worth the effort for a moving 
robot. It can work in very specific situations like running the square 
where the surface is nearly perfect.

Rather than looking for a better drive train look for a better way of 
determining location and attitude. That will depend entirely on the 
goals you have for the robot. Measuring the rotation of idle wheels is 
one possibility if you really need that speed and distance information.

You need to make sure you really need that information. For instance, if 
I attempted the Robo-Columbus competition I would rely on travel time 
and vision processing with no odometry.



- 73 -
*Rud Merriam K5RUD
* /Mystic Lake Software <http://mysticlakesoftware.com/>
/

On 01/04/2015 03:46 PM, Julia Jordan wrote:
> Markus,
> You might put a dot on your wheel and add a revolution counter as a way to calibrate your quad encoder math.
> Bob
>
> --- markus at bibi.ca wrote:
>
> From: Markus Lampert <markus at bibi.ca>
> To: DPRG <dprglist at dprg.org>
> Subject: [DPRG] Odometry and backlash
> Date: Sun, 4 Jan 2015 12:21:31 -0800
>
> Hi,
>
> I am adding odometry to one of my robots and found a rather large variance in my calibration runs. As it turns out my gear motor has some backlash resulting in ~1 degree of heading "wiggle room". The quad encoder sits on the motor shaft, not on the wheel itself which means they don't pick up on the backlash at all.
>
> I could not find any methods for backlash compensation other than for CNC machines, which doesn't seem to translate to mobile robots.
>
> Is there a method to compensate for it or am I in the business of finding a 'better' drive train for my robot?
>
> Thanks in advance,
> Markus
>
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