When first planning our robot we decided that car starter motors would make good drive motors as they are so powerful and cheap. After looking up some specifications from various car manuals we realised that finding speed controllers for things that could easily draw in excess of 400 amps would be difficult. Finding that they only spin in one direction was the last straw and we decided to look elsewhere for motors.
After receiving some in formation from Mentorn, which included a list of suppliers for various parts. We phoned several suppliers on the list, the Bosch 750w motors seemed very good. But considering that we also had to purchase some speed controllers, batteries and radio gear we decided that we just couldn't afford £190 for a pair just yet.
LNext we started looking into wheelchair motors as a good alternative. Another session with the yellow pages and the phone yielded a second hand mobility aid dealer, a few miles away. The owner of the shop buys cheap, second hand wheelchairs and scooters, fixes them up and sells them on. One four wheeled scooter he had bought had an unfixable fault with the controller and he had broken it up for parts. He sold us the four drive motors (one per wheel) with wheels.
The motors come attached to a 40:1 worm and wheel gear box and the output spindle takes the wheel directly which is held in place with a split pin. The gear box is held on with a carrier which consists of a plate which sits against the end of the motor (the silver cylinder) with threaded rods which secure the gear head with nuts. We have used the plates welded to the end plate to attach the motor to the chassis, as shown in this picture. Although not shown in the picture the motors are also attached to a rail running along the top of the motor by a bracket attached to the threaded rods and nuts for the rear motors. The front motors are fixed to the rail by a rubber exhaust mount, giving some shock and pressure relief if we get something heavy on the front. Because the rubber mount is threaded into a nut inside the rail, it can be wound out to give greater front ground clearance. This is obviously not shown in the picture above, I will update the photo when the next batch of photos are developed.
According to a sticker on the motors, they are rated at 24v and were made in 1989 (happy 10th birthday!). A large ammeter revealed that stall current is 40amps per motor, If anyone could suggest the likely nominal wattage I would be grateful. The connections to the brushes are spade terminals mounted on top of the brush carriers. There is a slide off plastic cap holding in the spade, when removed the spade pulls out with the brush on a cable.
