Mr Roche and I spent some time test-fitting the mechanum wheels and gearboxes and discovered some serious shortcomings of the AM14U2 chassis we were supplied with.
Problems
- Due to the added flanges on the new chassis kit’s inner rails, the clearances for the mechanum wheels are inadequate, so the wheels’ bolts will hit the frame.
- The flanges are arranged in an “S”, not a “U”, and the frame is slightly too narrow for the Mechanum gearboxes we own to fit flat against either side. The new design gearboxes are slightly narrower, but are out of stock and back ordered until next week, at the earliest.
- Cutting the flanges off to make new clearances will severely weaken the kit’s inner frame pieces, which are already riddled with so many drilled holes.
- (And here is the killer…) The center ground clearance is only 1.5″, so the robot will not be able to drive over the Stacking Platforms without getting hung up or “high-centering”. We’d have to drive around them every time! And swim noodles are 2.6″ in diameter…yikes! (This is something to scout potential alliance partners about! They will have special requirements in Autonomous and take extra time to maneuver the course.)
Solutions
- We decided to fabricate special new inner frame rails (out of 6061 T6 tempered aluminum sheet 1/8″ thick – tough stuff!)
- The new frame rail’s top edge is basically identical to last year’s AM14U frame, but the bottom edge has been extended downward in two places so the gearboxes can be mounted in a vertical orientation (that is “portrait”, not “landscape”). This raises the the belly of the bot about 2.5″. Running over swim noodles should pose little danger of getting stuck (but tipping over? Hmm….)
Work to be done
- The frame rails need to have a few 1/4″ mounting holes drilled along the top edge. (Put in two holes about 3/4″ below the top edge and bolt the plates together so you can “match drill” the following holes.)
- Inspect and file/sand any remaining rough spots off the frame edges.
- Drill the 3/4″ holes for the axles to pass through.
- Drill and install a piece of light angle to support the floor and battery tray. (Ask Mr W exactly where to put this so it reinforces the gearboxes as well.)