DEWBOT VII Arm Drive What to do, post-FLR?

Situation status quo  Arm is driven using a 15mm wide HTD5 synchronous belt – 500mm long – this is a “nothing special” belt We shredded two of these belts in playoffs – teeth sheared off  Drive motor is 2011 FisherPrice with a 256:1 reduction Banebots 4-stage planetary gearbox delivering: 101 ft lb f torque at stall 1.35 rev/s unloaded speed  There is 56/20 (2.8:1) pulley reduction from gearbox to arm  The motor is too fast – slowed in software  Deux uses an earlier FisherPrice motor. They are not the same. (could account for “jitters” in prime’s arm)

Objectives  Must - Adopt a more durable arm drive mechanism that the current one  Desired – Increase the amount of mechanical reduction between gearbox and arm – relax software speed limits

Constraints  The arm pivot is 3.063” (CAD model) from the back of the robot frame – this constrains the diameter of any sprocket, pulley or gear used to drive the arm  We should continue to use the FisherPrice motor and Banebots gearbox  Gearbox shaft is ½” (keyed)  Arm shaft is 3/8” (keyed)  There is a need to be able to manually lower the arm with the robot powered- down

Arm drive options  Pulleys – status quo  Type 35 steel chain & sprockets  Spur gears  Helical gears  Worm gears

Pulleys  A significantly stronger belt would be needed  There is room for a larger driven pulley than currently used  Low probability of delivering needed durability  Do not pursue

Type 35 steel chain & sprockets  Easy to execute Existing motor mount & tensioner should work Parts either on-hand or easily & inexpensively obtainable  A 42:10 (4.2:1) reduction is feasible  Well-known ground for the team  Probably strong & reliable enough  Chain drive will have some slop & nonlinearity – tensioner should limit slop & backlash.  Probably fits in budget without compressor change

Spur Gear  Stronger  More linear than chain – some backlash  Requires precision fixed mount plate for arm pivot pillow blocks & motor  84/15 (5.6:1) reduction possible  More costly – compressor change will be needed  Parts are obtainable

Helical Gears  Stronger & smoother than spur gears for same contact area  Most linear  Requires precision fixed mount plate for arm pivot pillow blocks & motor (same as spur)  Expensive (but probably in-scope after compressor change)  Limited parts availability  ~4:1 reduction seems to be limit, based on findings so far.

Worm Gear  Mounting would be challenging  Generally cannot be back-driven – a problem for us  High reduction possible  Basically, doesn’t meet the problem’s needs  Do not pursue