2021-06-26 Mech Meeting Minutes - Drivetrain Design Review

Goals

Update & Action Items

Questions for Mentors

• Mounting of wheel plates - key both shafts?
• Shaft diameters?
• Dummy bar / moving differential to top
• Aluminum plates to mount differential bushing
• Thoughts on L gussets (probably don't need)
• Connecting rod on differential bar
• Make differential more adjustable, make the rod ends able to change in both directions
• Differential - top, bottom, make shorter, etc?
• Differential shaft mounting - have more mounting features on top, or have perpendicular feature on bottom
• Center gussets - add more holes

New Tasks

General Notes

• Cross bracing would be useful
• Get ready to iterate on the spot (Robert Molloy- goes by cory)
• What kind of weights/masses would you use? (Use plate weights, like weightlifting)
• Just weigh the material, put it on a scale. Etc
• Careful stress concentrations shearing off
• look at yield strength of the material relative to the stress on the keys
• Use online keyway shear strength calculators
• Marks (textbook, useful)
• Maximize the hub length (shear calcs will drive things here)
• Oversize by factor of 2 or three
• We have basically 2 by 4 stretching between that, and we're cantilevering it off everything. We're only really off 1 bearing in particular.
• Take a look at shaft deflection standpoint wrt weights and stuff.
• We don't have a separate bearing support on the end wrt the gear box (scary/bad)
• Bevel set reduction from versa planetary (90 degree offset), motor sits flush with 2x4
• try testing with some wheels removed/broken
• Remember to calculate reflected loads
• Try to 3D print or paper print templates so you can just mark holes and go (instead of trying to utilize drawings, make it a 1 to 1 sample and cut with the saw)
• Loctite is useful
• Make sure we have enough planetary sets to do smaller increments (1.5 margin over what we have, and get a 0.75 margin below) customizability is key
• Tough time turning, why? : When you turn ,you're running with a drivetrain that has friction points close to the ground, you're dragging all of that. Drivetrains themselves drop the centrewheel to drop the wheel base. (he'll send whitepaper), shorter wheel base affects turning radius, and
• affects lever arm to the wheel. Shorter wheel base = better turning elements, accomplish that by dropping centre wheel in that case. 
• High reflected torque through friction needed to turn
• recommended back wheel be slightly higher, from rocker standpoint, if our centre of gravity is forward, and we touch on the front and middle wheel. That will adjust the position of itself.
  
• https://www.vexrobotics.com/217-6293.html?___store=vexroboticsca&___from_store=vexrobotics
• Things won't be perfect the first time, we spend so much time on the analysis etc, but then things don't work and you'll need to fix these small marginal things to make things way better.