Wiper-motor powered forklift toy
So on my most recent trip to my parents, I brought it back to my shop.
Each of the two cogged wheels is powered independently by a windshield wiper motor. The cog wheels were originally round wheels, but I experimented with adding caterpillar tracks. But the tracks made it nearly impossible for it to steer, so I switched back to two wheels and a caster, but I kept the sprocket wheels.
The mechanism for raising and lowering the fork is made of two hand-cranked window lifters from a 1970s car. But the whole lifting mechanism was seized up. Taking the window lifters off and adding oil and turning them with locking pliers, they moved again. I cranked them up and down a few times with a drill until they turned easily again.
Un-seizing the windshield wiper motorNot having a spare motor, I opened up this one to see what might be wrong with it.
The rotor was stuck in the back housing. I cut two pieces of wood to clamp some locking pliers to the shaft without damaging it. But it wouldn't budge coming out. I could spin it just barely, but I was pretty sure I was spinning the bearing itself (shaft seized in the bearing)
But some WD-40 sprayed onto it cleaned it off very quickly.
A curious thing about this motor is that it has three brushes. Speed control was achieved by connecting power to different brushes on the motor. In some ways this is inelegant, but still more efficient and more consistent speed than having a resistor in series with the motor. By connecting power across brushes that were closer together, there would be less induced back-EMF, allowing the motor to run faster from the same input voltage. More on how this is wired up in a car here
Cleaning it upThe whole thing was covered in a layer of dirt and dust from having been in the attic all this time.
Having removed all the hardware and brushed off as much dust as I could, I took it to the belt sander to sand it down a little.
I also sanded down the drive sprockets on my strip sander.
Looking at the whole thing, I have to say, I have gotten much more meticulous about building stuff since I was 16. But I also have much better materials and tools available now. And possibly, I'm spending more time fixing this thing than I did building it in the first place.
I made the original drive tracks relatively long so that the rear axle would clear the lifting mechanism. But the long tracks, unfortunately, made it just about impossible to steer it in anything but a straight line, especially on grass. So I switched it back to two wheels and a caster.
But with the caster now ruined, I figured I might as well try to make the tracks work. Shortening the tracks substantially makes it more like a small skid-steer loader, or this other this tracked toy that I also built back in 1985.
I wanted to reuse the extra sprockets. But I noticed the glue joint to the extra layer was cracked, then noticed the whole sprocket was warped and shrunk by several millimeters in the cross-grain direction.
Apparently, the maple wood I used for these wasn't fully dried when I made them.
So I measured the parameters of the chain, then used the "sprocket mode" of my gear generator program to generate a shape for new sprockets,
which I printed out...
... and cut out on the bandsaw. I used my strip sander to smooth the cogs.
I previously used a 1/2" dowel for the back axle, but a steel axle would be better, and I had a piece of 3/8" steel rod kicking around. I also glued an extra layer of wood on the sprocket around the hole to give it more stability. Again, I have much better materials available to me now than I did when I was 16.
Conveniently, the mechanism already had a big hole right where the notch needs to be.
The nail fits loosely around the block in the middle, but tightly in the blocks on either side. The nails rusted a bit since I built it, and that also helps to lock them in.
A spring will hold the axle so the chain is fairly taut, but the axle can move a little in case something gets caught in the chain and sprockets.
The brackets screw on from the top, through the rails that the window lifters are mounted to. The chassis of this forklift is only 1/4" thick plywood, and not even very good plywood. So screwing through the rail on top into the bracket on the bottom gives it much better support.
With a total of four wiper motors and no electronics or relays, I need four wires plus a common ground to connect all of them. I made a five lead strand by braiding together two lamp cords plus a thicker piece of automotive wiring for ground.
I also temporarily put the old cable mast back on it. The cable mast makes it easier to avoid running over the wires.
I made two switches to control the tracks out of copper wire. Actually, I'd made these when I made the videos about this tracked vehicle in 2008. One side of each motor is always connected to ground, and the switch will connect the other side to either +12 volts or -12 volts from a homemade bench top power supply (similar to this one, but using a variac instead of a tapped transformer, and with a center tap).
Back to my woodworking website.