A good design, Madison. I've tried to convince several of my teams to try something similar for quite a few years now (and in fact I suggested this
exact config THIS year, too!) But many of them are younger, smaller, still developing teams, and were a bit afraid of attempting a complex drive train in
addition to focusing on designing complex
payloads (like programmable shooters, rotating turrets, and non-jamming ball lifts).
Quote:
Originally Posted by AllenGregoryIV
This looks really great I have a couple questions [...]
1. Why did you choose to pivot the traction wheels down instead of moving the mecanum wheels?
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IMHO, you should
always hard mount the mecanum wheels to the frame, and
never have them dangling on the end of a pivot arm.
Remember... The forces generated by a single mechanum wheel are always at
45 degrees to its facing direction. (The thrust vector is always along the wheel's roller axle direction, as viewed touching the
floor, not the top of the wheel.)
That means for every pound of thrust forward or backward, there is also a pound of thrust
SIDEWAYS applied to the frame. Therefore, placing it on the end of a pivoting arm adds significant moment arm
sideways forces to the pivot joint. IOW, under normal operation, a mecanum wheel at the end of an arm is always trying to BEND your drop arm SIDEWAYS... (
Not a good idea...)
OTOH, when you place the mecanum wheel at the chassis and the
BARREL on the end of the pivoting assembly, the barrel always applies its reaction thrust
along the direction of motion, which is then transferred
directly along the side plates of the assembly back to the axle, very near to where it connects to the base frame. NOW the only sideways torque is when someone crashes into you and pushes your bot from the side... (Oh yea... Be sure to remember to design to accept
that!
)
BTW... This also means you in addition to the normal roller bearings, all mecanum wheel stacks (whether pivoting or not) should also
always include
Thrust Bearings in its design. Simply place one on on each side of each mecanum wheel before adding your spacers. They are not that expensive. This keeps you from losing efficiency from side force friction of the mecanum wheel pressing against the frame, and therefore helps assist in transferring maximum vector thrust force to the frame with the least loss.
I hope this helps!
- Keith Mc
--- Also the List Dad of "OmniMec" - An omnidirectional and mecanum wheel specialty e-list ---