Will center drop affect our auto routine

[Ambrose]

We’re trying new things this year and don’t have a lot of resources so we are wondering, if we design a center drop drivetrain, will the rocking from front to back affect autonomous routines? It seems like it would affect turning of the robot, but not sure if it is significant. Also not sure if we should try to weight the robot to one side or the other to negate this if it does exist.

[GeeTwo]

If your CoG is forward or aft of your center wheels by more than a couple of inches, and you don’t accelerate too much, you should get a pretty consistent drive. If you use motion profiling, even if it rocks, it should rock consistently as long as you don’t move your CoG too much.

[BordomBeThyName]

Edit: listen to Jared and Nick.

@Jared_Russell

So I used to believe this, but lots and lots of firsthand testing has shown me that the actual CoR tends to be far closer to the geometric center of the 6WD than either of the stable polygons. I think this is because in practice most of your mass is being instantaneously supported by the middle wheels regardless of which way you are rocked.

Yes, having a center drop will cause your robot to pivot either around the blue or red circles on the picture below, depending on which wheels the weight is resting on.

As you correctly suggested, you can help this by keeping your CG on one side instead of centering it. However, if the path your robot is driving on is consistent, then which wheels it’s on will also be consistent, and you shouldn’t see much variation, even with your CG in the middle.

[ProPain37]

Have you guys never used the KOP frame before? It comes with a center drop built in.

[Ambrose]

Auto is new. Center drop is not. Sorry I didn’t make that clear.

[Jared_Russell]

So I used to believe this, but lots and lots of firsthand testing has shown me that the actual CoR tends to be far closer to the geometric center of the 6WD than either of the stable polygons. I think this is because in practice most of your mass is being instantaneously supported by the middle wheels regardless of which way you are rocked.

[Nick_Coussens]

This has been our experience as well, especially if you have omni wheels, etc. for the corner wheels instead of traction.

Teams in the past have done more drop then needed to guarantee that the middle wheel is always getting an accurate reading of odometry relative to how much the robot is actually moving. If you do no drop or a small amount, there is the possibility that uneven carpet, venue floor (hey, no more MMP stage!) will make it so your middle wheel is not supporting the majority of the weight of the robot and thus change the center of rotation, etc.