The m&m’s candy tin used for the body is slightly narrow, which makes it slightly more difficult to find motors that will fit. There is a compact Copal gearmotor that I use in sumo robots such as No.2. Those motors would just fit end-to-end in Yummy.
Electric motors end-to-end versus side-by-side
Right-angle gearmotors may be a better choice for narrow robots. In this case, the Faulhaber motors have a much higher gearing (141:1) over the Copal motors (30:1). The robot will drive at a more leisurely pace with the Faulhaber motors, which is what I prefer for this robot.
An issue to keep in mind with right-angle gearbox motors is that the motor weight is not directly over the wheels. This results in less traction for the wheels and more friction for whatever part of the robot is bearing the motor weight. This made for intolerable slippage in Open-Face Sandwich. However, if other elements in the robot, such as the battery, will counterbalance the right-angle gearmotors, then it may not be a problem for your robot.
Yummy has four wheels. The front wheels have rubber bands for traction. The rear wheels are narrow, slippery, and rotate freely. As such, the portion of the motor weight loaded on the rear wheels does not have a detrimental effect since the rear half slides so easily compared to the front wheel traction.
Nevertheless, I ran into a tripod effect with Yummy. That’s where a four wheel robot tends to rest on only three wheels. Placing a stack of quarters over the powered wheels generally ensures that they will always make contact with the surface, so that the robot won’t be spinning a wheel off the ground.
The plastic 90-degree drive box at the end of the Faulhaber gearmotor has a pair of mounting tabs with holes. These are not necessary in Yummy and take up precious space. Also, the motor output shaft needed the belt gear removed so that a coupler can connect the gearmotor to the wheel.
Faulhaber gearmotor with top of assembly cut off and belt gear removed
I used a milling machine to slowly cut away layer after layer of the plastic tabs. Although this results in a clean, flush drive box, it was overly time consuming and unnecessary. For the second motor, I changed machining tactics. It was much faster to cut it off with a Dremel cut-off disc and then finish the last millimeter with the milling machine.
Milling away a portion of the right-angle gearbox bracket
The Faulhaber motors include an encoder that won’t be used in Yummy. Nevertheless, the motor has a six-pin connection rather than a standard two wire DC motor connection. Rather alter the motor wiring, I created a simple adapter on a breadboard.
Left: Header to connect to Faulhaber motor pins. Right: ShapeLock acts as electrical insulator and wire strain relief
The adapter was then coated with ShapeLock low-temperature melting plastic to prevent short circuits when floating around in the robot’s guts.
Motor connector adapter plugged together inside a metal body with nearby circuit boards
Physically attaching the motor to the candy-tin was lot more difficult. It required making a motor-mounting block, which we’ll see next.