Hi. My team is almost done constructing the drive base from this years FRC kit. We noticed that the middle wheel on each side is slightly lower (just a bit less than 1 cm) than the other wheels. Because of this, our robot rocks slightly forwards and backwards. We have checked everything over and nothing seems out of place and we simply used the pre-drilled holes so we are a bit confused. Has anyone else had this problem? Is it intentional and if so, why? Thanks so much!
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It is very much intentional. That’s a 6WD “drop center” drivetrain, meant to give better maneuverability than a 4WD or a 6WD “flat” drivetrain. You can use other holes or otherwise make changes as needed.
I would recommend trying to weight the drivetrain towards one side or the other for competition use.
Yes it is intentional and it is done so that you can actually turn the robot and so that it turns consistently.
The drop center places the majority of the weight on the center wheels, assuming the CoG is not at ether end. That means they grip while the other pair currently touching the ground can slide sideways as you turn.
Thanks so much for all your help!!
On this note though, if you were to use the other two bearing holes to mount the other wheels (so replace the long screw wiht bearings and axle), could you still use one of the belt thats came with the KOP or get a new one?
The center distance would be different so you would either need a smaller belt or larger pulleys.
I was wondering about this recently. Does weighting your drivetrain toward one side improve maneuverability? It seems like the robot would still rock back and forth when accelerating.
Sort of. It actually makes it so that it rocks less. You’ll still rock in acceleration, but you’re mainly on a shorter wheelbase so you maneuver better.
Basically the idea would be to weight the robot such that it favors 4 of the wheels in while sitting, but can still rock while turning to effectively shorten the wheelbase during those maneuvers. A long wheelbase puts more strain on the wheels, whereas a 6wd drop more or less halves the length of that wheelbase while turning.
Isn’t the shorter wheelbase a result of the drop center in general not a result of the weighting? Am I correct to say that the primary reason for weighting is so that mechanisms don’t move when the robot is stationary/moving slowly?
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Correct on the first, mostly correct on the second. If weight is balanced over the center wheels, the robot will also not rock when it is accelerating in a constant direction; it will remain on the wheels on the side it is accelerating away from and rock when the direction of acceleration changes. Deliberately imbalancing the load gives you a more stable/predictable orientation for picking up game pieces and scoring goals.
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