DEWBOT VII Arm Drive

1
DEWBOT VII Arm Drive

• What to do, post-FLR?

2
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 2561
  reduction Banebots 4-stage planetary gearbox
  delivering
• 101 ft lbf torque at stall
• 1.35 rev/s unloaded speed
• There is 56/20 (2.81) 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
  primes arm)

3
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

4
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

5
Arm drive options

• Pulleys status quo
• Type 35 steel chain sprockets
• Spur gears
• Helical gears
• Worm gears

6
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

7
Type 35 steel chain sprockets

• Easy to execute
• Existing motor mount tensioner should work
• Parts either on-hand or easily inexpensively
  obtainable
• A 4210 (4.21) 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

8
Spur Gear

• Stronger
• More linear than chain some backlash
• Requires precision fixed mount plate for arm
  pivot pillow blocks motor
• 84/15 (5.61) reduction possible
• More costly compressor change will be needed
• Parts are obtainable

9
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
• 41 reduction seems to be limit, based on
  findings so far.

10
Worm Gear

• Mounting would be challenging
• Generally cannot be back-driven a problem for
  us
• High reduction possible
• Basically, doesnt meet the problems needs
• Do not pursue