Design Process
Guidelines
- 3 ft/s: Very slow, very good pushing force
- 4-7 ft/s: Slow
- 8-12 ft/s: Medium, medium pushing force
- 13+ ft/s: Hard to control, little pushing force
- Teams have done it successfully, but it may require some fancy programming
Motor Curves
- Very valuable source for designing mobility systems
- Usually torque on x-axis, all other variables on y-axis
- Max power the most important single characteristic
- Motor can always be geared to get correct speed/torque
- Check stall current; be careful if much higher than circuit breaker limit
Gearing
- A simple pair of gearboxes will almost certainly be included in the kit
- Very quick to build
- May not be as powerful or flexible as other methods
- DeWalt drill gearboxes
- AndyMark gearboxes
- Designed and built by two extremely experienced FIRST veterans
- Two-speed, shift on the fly gearboxes
- Adapters available for a variety of motors
- AndyMark
Power Transmission
- Keyways
- Pins
- Set screws
- Can come loose easily; Loctite if using
- Bolts
- Very effective for large gears/sprockets, but annoying when connecting multiple things
- Hex shafts
- Very strong, easy to assemble
- Gears, bearings available at AndyMark
- Need a hex broach if using other gears/hubs
- Can turn down shaft end to fit in bearings
Traction
- Often the most important factor in determining pushing force
- No metal or hard plastic cleats, etc. allowed
- Supplied wheelchair wheels have quite low traction
- Rubber treads or conveyor belting attached to wheels
- Innovation First supplies pre-made traction wheels
- Pneumatic wheels
- Good for shock absorption
- Test on actual carpet!
- Too much traction can make it too hard to turn
Computer Aided Design
- Use sketching tools to design drivetrain layout
- 3D CAD model of drivetrain useful
- Ensure quality of the final result
- Easier to design functional attachments
- Can be used for virtual prototyping
Testing and Practicing
- Test beyond what the robot will likely experience
- Test many times in different circumstances
- Reinforce weak areas
- Tweak components
- Build spare parts for suspect components