# Robot's turning center

This GPS KB page discusses the turning center of a robot.

https://kb.vex.com/hc/en-us/articles/360061932711-Using-the-V5-GPS-Sensor

I’m curious as to what you all have found to be an accurate/best way to find the turning center? Use the halfway points of each side of the chassis? Or have the robot collect data as it turns then use the data to help calculate?

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I haven’t used VEX AI, but I don’t think it matters how you calculate it for this. If you enter (0,0) as the offset, then the GPS sensor will return its own coordinates on the field. I think they added it as a matter of convenience to convert to robot center coordinates.

It will also depends on how accurate GPS is at determining true heading from its imager or internal gyro. If it’s off and you have better heading from wall alignment, then you may be better off converting coordinates yourself.

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we just put in a random relatively close coordinate on our chassis, told the gps to go to 0,0. If it lines up with the actual center of the robot then it works, but i assume it’ll be much easier just to use a metric ruler, as the sensor is very precise so wrong measurements could be bad.

Many ways to do this.

Method 1:
If you have traction wheels or locked omnis, find the midpoint of the segment that connects them. This does not work if you have more than 2 locked omnis/traction wheels.

Method 2:
Eyeball it. Drive your robot around and see at what point does it turn around. Probably the fastest method.

Method 3:
If all omniwheels, find intersection of diagonals through the center of omnis

Note:
full-traction wheels cause turning scrub, so the center of rotation often is not precise.

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Thanks for the helpful info !