Hardware design and implementation - strategy and goal

[Louis L]

This posting may be used provide content for Arcadia.

Highlights

   
• Analyze the challenge and decide what features the robot will have
• Select a drivetrain. This is an early decision if parts need to be purchased - do this before supplies run out of stock on the more complex or unique products.
• Avoid over-building as this just makes the robot heavy
• ... but also don't make the robot flimsy as it'll just need constant repairs. A bored pit crew with nothing to do but changing the battery is a good thing.
• Avoid connecting parts on top of other parts. Component A is attached to chassis. Then B gets attached to A. When A needs to be replaced, B needs to be removed first. It's better to mount B to the chassis than attach it to A.
• ... likewise sharing mounting holes or even mounting parts in close proximity makes for messy and lengthy repairs.
• Generally speaking, design so that the robot is easy to service and repair.
• Use limit switches and sensors for closed-loop controls.
• Use cable conduits to avoid chaffing of wires on metal parts.
• Use Euro-style connectors to extend cables - they do not require additional connectors or crimping or soldering; just strip the wire and tighten the screw.
• Wires should have service loops and strain relief.
• ... they should also be labeled for easy identification on either end of the run.

[Ed B]

Related to overbuilding:

• Robustness can be had without overbuilding and an overbuilt robot can still be flimsy.
• Flimsy has two consequences: a robot that breaks often and cannot handle physical play, a robot that does not perform well on the field because it is not rigid where it needs to be.

connecting parts to other parts ---> modular design

Other items (use what seems appropriate for the message):

Use ad-hoc bearings like a bolt through a hole only where wear is going to be minimal and precision is not important.  Otherwise use proper bronze bushings, ball bearings, appropriate plastic bearings, etc. Never use Aluminum on Aluminum for bearings.

Don't overload gear boxes.  Particularly with high ratio planetary gearboxes, it is possible to develop enough torque to break an output shaft.  Keep in mind that during interaction with the field, other robots, and game pieces, actuators can apply dynamic torque that far exceeds the torque provided by the motor/gearbox.

provide two bearings on shafts longer than 5 or 6 times the diameter of the shaft or when actuator side forces can be large.  This can include the motor or gearbox output bearing.

remember that motor and gearbox mounts see all of the torque their output shafts see.  Build accordingly.

Mount motors and gearboxes the way they were designed to be mounted, not with u-bolts, hose clamps, etc. Do not use the motor part of a gear/motor combination for mounting.

Chain drive bearings should be in the same piece of metal or at least in the same module of the design. Use pins to prevent slippage between bearings.

Don't use limit switches or other sensors as mechanical stops. They will break. Locate limit switches where they can be adjusted.  Account for coasting or backdrive where limit switches stop a mechanism. Use limit switch features on motor controllers where you can.

Avoid set screws for fixing pulleys or sprockets to shafts.  Use keys or clamping collars where possible. Sprocket and pulley bores MUST match shaft size or an appropriate shaft adapter.

Plastics: Polycarbonate for strength and flexibility.  Avoid acrylic if possible and certainly where strength/flexibility is needed; acrylic cracks at edges and holes. HDPE is tough and makes a good bearing surface with aluminum or steel. LDPE is almost as good, but softer. Delrin makes good bearings, too.