Great link, thanks for posting! It's a very simple method, construction wise, of creating a drive module capable of moving in any direction.
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Originally Posted by PAR_WIG1350
cool, but one of the issues I see with scaling this up to frc size is that each drive unit would require 2 steering motors, on the other hand, a common shaft could be run through the robot from which all wheels are powered through chains and universal or cv joints. But still,the minimum number of motors for a robot supported entirely on its driving wheels is seven if three wheel units fed from a single motor driving a common shaft. if only two driving units are used, that drops down to five motors, but you now must support part of the robot on non-powered wheels which reduces available traction.
The greatest disadvantage would be that both the seven and five motor versions that I mentioned use only one motor for actually driving. in comparison, a six motor swerve drive configuration uses three of the six motors to drive and a four motor meccanum system uses all four motors to drive, but at reduced efficiency due to canceling vectors.
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Just because the drive modules used in the video each use two actuators doesn't mean you'd have to implement it like that on a FRC robot.
For some systems it's easier to think about it in terms of degrees of freedom (DOF); for example, the typical "full swerve" drivetrain is able to move in x, move in y, and rotate... a total of 3 DOF. 3 DOF can ideally be obtained with just three actuators.
As an example, the Robonauts have effectively used a full swerve drive system in the past by using a crab drive (all modules steer together with one motor, all modules are driven together with one motor) with a rotating 'top' manipulator to give rotation. 3 motor inputs = 3 DOF.
Along that same logic, a typical six wheel drive train has two degrees of freedom: rotate, and drive forward/back. This requires two inputs, left side of the drivetrain and right side of the drivetrain. 2 motor inputs = 2 DOF.
The module shown in the video is intriguing because the tilting of the module acts somewhat as a gearing system. The further it tilts, the faster you can go. This effectively gives you a high gear at full tilt, and low gear with minimal tilt, as well as every gear in between (CVT!). So, tilt in x and tilt in y = 2 motor inputs = 2 DOF for a single module, the outputs being velocity and direction of travel.
Practically, I don't see a good use for this kind of system for an FRC robot. A simple swerve module already gives directional and velocity control (via motor speed controller). Any advantage that this system has in terms of variable gearing is most likely lost in the hemisphere/carpet interface... I can't envision getting a respectable amount of traction in low gear with such a system. The fact that it effectively works as a continuously variable transmission is appealing, however. I'd like to see one made, in Robonaut fashion! 4 modules tilting together with a central power plant to drive the hemispheres... 3 DOF for a CVT crab drive.
