Lego RR electric motor switch control
Hi All
I agree with all of you that the solenoid switch control was crude (see the beginning of this thread). I learned a lot with your help and now have a micro motor control solution. It only draws power when actually switching. It runs off 3 Volts , two AAs, that should last forever. It draws about 200 ma when the motor is running. The motor only turns a quarter turn, when power is applied , and is stopped in a stall mode. The torque developed is about 16 gram – cm. Since this torque is very low, the Lego train switches must be modified to remove the bumps on the switching arm.
The Lego box that houses the motor is a friction fit , and measures : 3 bricks high (H), by 4x5 (WxD) lego bumps footprint.
The control is a DPDT Toggle switch , the action is spring return to center, momentary on , center off, momentary on. The center poles are wired to the switch motor , with the outer poles criss crossed, and wired to the batteries . In operation the toggle is moved left or right and the motor responds by moving CW or CCW. The toggle’s spring returns the toggle to off when released.
The first three motors I tried, were removed from a dead DVD player. They measure about 1 inch dia x 0.5 inch deep, the shaft is 2 mm dia. Here is a source for new motors: cost $3. 50 USA. Switches cost about the same.
http://catalog.miniscience.com/catalog/motors/RF300CA.html
Remove the yellow switch arm. The bent wire below replaces it.The bent wire is coupled to the motor shaft with a short length of rubber tubing.
The bent wire is made from a three inch (76 mm) length of # 14 awg solid bare copper
A 90 deg bend at 1” from the end forms the shaft. Two loops are bent into the wire forming the manual over ride, and the actuation levers. The loops are formed by bending the wire around a 1/4 “ drill bit and a 1/8” bit. The height of the smaller loop (from the shaft to bottom of the loop) should match the yellow switch arm shaft to bottom dimension.
The coupling tubing is about 1/2” long with a 1/16” hole. As an alternate ; drill a 1/16 inch (1.6mm) hole through a pencil rubber eraser.