# Gear ratio affect of tracking and position trackimg

For a gear ratio like that, the slop gained would probably be less than the accuracy gained. I’m not sure how worth it it is though

This can be avoided entirely by tensioning the wheels down enough- to surpass the tractive effort needed to accelerate- but has the drawback of increased rolling resistance (which will be seen as power losses in the actual drivetrain).

It really isn’t worth it. Precision doesn’t really matter for tracking as the tolerances are quite large. Not having any slipping and having better accuracy/repeatability is way more important.

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we have our tracking wheels quite close to each other (becuase our frame is too thin to fit them in. Do you think it would be a good idea to use a gyro for the angle calculation in odom?

Also i now realize that they can be pushed one more inch by switching left and right

More data = better. You can use some math like the Kalman Filter to accurately combine the data from the two inputs

Edit: I wouldn’t solely rely on the gyro, as far as I can tell it has less accuracy but more precision(it drifts and will not be as repeatable)

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Those are probably too close together. You’s have to do the math though. Calculate resolution and determine if that’s accurate enough for you. For example, small wheels are good, but close together is not. So then at least get rough numbers to compare to see if it is viable for your code

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A high enough gear ratio would probably over compensate for the added slop though, right? I mean you’d still not net as much as you add, plus you have more unwanted friction, but it could work if you really need more resolution. However, there are better ways to gain this, some of which you mentioned

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You could just wait for the rotation sensor if you need more resolution. I’m pretty sure it has a resolution of 0.1 deg rather than 1 deg. I wish VEX released CAD models for their coming soon products so we could design for them before we get them.

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True. There’s a lot of ways to get more resolution, but using a better sensor is probably an easy one

That could work, I think

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This may sound dumb. But is there a way to mathematically calculate your x y, theta if you kind of “simulate” what the values would be like if the tracking wheels were further apart?

Yeah, most of the equations you can use are most easily accessible in the pilons odom guide. I personally couldn’t derive those equations independently, with my current mathematical background, so I would recommend using the ones they already have

Yes, one of the constants used in the PiLons odom guide is the distance from the tracking center to each wheel. So “simulating” in this case just means substituting a different value for this distance.

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well if you just literally substitute the value for something else then deltaL and deltaR wouldn’t be right then. and deltaL and R is what you get from the encoders.

In that case, could you rephrase your original question? What are you trying to ask?

so like you know your delta L and delta R with your current encoders. is there anyway to find that same deltaL and R for a different distance from center?
Say the orange arcs are the “new” deltaL and R

Oh, sure. The ratio between “new” deltaL and deltaR and the old ones will just be proportional to the ratio of the radii from the wheel to the arc center. (So say your deltaR was 10" and your arc length was 20". If you move the wheels 1" out your new deltaR would be 9.5").

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Just to clarify, when you say “arc length”, do you mean the distance from the robot’s tracking center to the track wheel?

Arc length is the length of the arc of the displacement vector