Building an electric scooter

Some lady was having a yard sale, and a day later, I found some stuff sitting on the curb. One of the things was a breadmaker! Sounds weird, right? Well, I guess you put the dough in one tray, and it spins and cooks the dough. I took it apart, and found 2 AC brushless motors. One was small, it was just for cooling (there was a 64 pin IC in there, I didn’t know they came that big!) and a big motor for spinning the dough. I really wanted to make…

An electric scooter!

However, upon testing, I found that the big motor failed to start itself. If it doesn’t have enough torque to start itself with no load, I can’t using that. It did seem to be pretty fast and torquey in the higher RPM band, but I was doubtful. So, I dug through my messy workshop, and found a HUGE pump motor (for my old furnace). Once I plugged it into the wall, I knew that this was it. It started right up, and (according to the label) spun at 3450 rpm, but due to it being like 10 years old, that has probably settled down a little. This would be perfect for making an electric scooter. One problem. It runs on 120 volts AC.

Well, I have a car battery, 12 volts. But it’s DC. I also have an old 12 volt DC to 120 volt AC inverter, but it’s probably very inefficient. SO, I was wondering, how do you make AC from DC? I was thinking, if i made pulsed DC current and put it through a transformer (to get 120 volts DC) and made 2 transistor oscillators, with big power MOSFETs, I could do something what that. The 120 DC would be split into 2 circuits that are in parallel, and one circuit would be connected to one oscillator circuit, and the other circuit of the 120 DC into the other oscillator circuit, in the opposite polarity. Therefore, if the timing is right, one oscillator circuit will be one while the other is off. They both keep turning on and off, and since they are of opposite polarity, it simulates the AC wave, going from positive 120 volts to negative 120 volts. I’m not sure that this is right, it’s just a theory. But can you think of a different way to do this? Thanks! I really want to make this scooter. It would be awesome!


Wow, that’s awesome! Idk how that kind of stuff works, though, because I just joined the Robotics Team so yeah…

Without going into details, if you are replicating the functionality of a 12VDC to 120VAC power inverter, how about just using one that is already built?

I think your best solution, though, would be to find a used 12VDC motor. You can buy an FRC 12VDC CIM for about $25 or so, and it should have more than enough power. You can then beg, borrow or steal some big fuses or circuit breakers, an IFI controller, a kit transmission, and a motor speed controller (IFI Victor?) and have some fun.

You might look around Chief Delphi for some pre-2009 posts on using CIMs in robots. Those teams solve the same problems you are trying to solve all the time. Who knows, you might find an FRC team that would like to unload some of their IFI gear for a reasonable donation. :slight_smile:

A 12 volt motor would be by far the easiest option. Tinkering with 120 volts isn’t that safe either… If you have to go with the 120 volt motor than you might want to try this circuit I found after a quick google search: Schematic

Thanks for the schematic, Vexer. That’s almost what I had in mind, 'cept mine didn’t require the capacitors (but I did need 2 more transistors.)

And Rick TYler, do you happen to have the specs (torque, speed) of the CIM motors your were talking about? I found them on the IFI website, but no information about them is given, and unfortunatley, they won’t be in stock until next year! I also saw that the control systems are really expensive… I mean thousands of dollars… so, what would you consider a “reasonable donation”? I can’t wait to get this this working!