Where to put tracking wheels for Odom

Hey, I was wondering how far I need to have the tracking wheels, and where to place them. Looking at 5225As doc helped me a lot, but I didn’t really understand where to actually put the tracking wheels. I think, from the like 20 posts I looked through, we just place them as far away from the center as possible, but idk. And yes I used the search bar lol I just didn’t see anything

You do want to place parallel tracking wheels as far from the center of rotation as possible, because when the robot is turning, wheels which are further out will spin a lot farther, which gives you higher data resolution. As for the horizontal one, I don’t believe it really matters where you place it from what I understand about odom.

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I like using two tracking wheels plus an inertial sensor, in that case it doesn’t matter where they are as long as they don’t point in the same direction.

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My team and I have made a drive train with the two perpendicular encoded wheels and an inertial sensor. We did the math and it is very close to accurate but after about 15-30 seconds of driving it got a couple inches off. I was wondering if this is perhaps mechanical as our two perpendicular wheels are very close together although mathematically it wouldn’t seem to matter. Our main problem is when we make a zero turn the position changes which it shouldn’t because the track wheels inputs should cancel each other out. Anyways, I was wondering as someone who has more experience with odometery if you were able to get it with pin point accuracy as well as any advice as we try to refine our code

Well I’m not experienced with odom but the inertial sensor definitely is a problem. You should have a third tracking wheel, it helps a lot with accuracy since inertials and gyros have drift

Not really, inertial sensors are fine for odometry. I have seem multiple teams that are successful with them. Tracking wheels can be as problematic as the inertial sensors since any imperfections in their build quality will result in error buildup.

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Yeah, but build quality can be resolved. Just try your hardest to make it work at max efficiency. Inertial drift is a serious problem that CANT be fixed.

The level of success and reliability that teams have gotten from using an inertial sensor would indicate that inertial drift is not a serious problem, especially not one that makes inertial sensors inferior for use compared to 3 tracking wheels. As much as I love to bash the reliability of vex products, I can’t say anything bad about the inertial sensor.

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