How to select an electric motor for an electric go kart?

Hello, everyone! New member right here. I’m currently designing an electric go kart but got stuck at deciding the possible motors that could fulfill my need. Specifically, I want to determine the starting (stall) torque of the motor and its no load torque. I don’t know if my reasoning is correct as to why I think these values are what I need in order to select a motor, so I’ll explain the whole process just in case I’m wrong and you can correct me (please do!). Okay, so my kart weights approximately 150 kg (330.6 lb). According to my calculations, considering the weight distribution between the front and rear wheels, rear wheels diameter, etc, I need a 294 Nm (2605.3 lb in) torque in order get the kart moving. Now, I will use a chain drive in order to transmit the torque from the motor to the shaft. So I just want to be sure that the chain I select won’t brake when the kart accelerates off the line. I’m familiar with different motor selection and performance analysis concepts but I’va found it hard to find this torque values. Specially since the data given by the majority of vendors (in Ebay, and Amazon) only say the power of the motor, and the rated voltage and current, and also the max speed of the motor. So the real question, iguess, is how do I use this little amount of data to select some possible motors for my kart? I should also mention that I will use a permanent magnet DC (PMDC) motor. Hope you guys can help me!!! Thanks a lot, community!

Not really help, but a good memory about an electric go kart my father made for my brother and I when we were kids. Believe it or not this was over 50 years ago! He worked at an aluminum factory so he built the frame out of aluminum so it was light. The motor was a car generator hooked up to a 12-volt battery. A fan belt connected the generator to a pulley on the axle. The accelerator was just a switch and of course it was just on and off. It went like hell on a fresh battery! Of course it didn’t last long due to the fact of the aluminum frame and two kids running it into the concrete parking barriers! We had a lot of fun putting it back together and of course wrecking it again. Thanks for the memories!

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all I know is that if I wanted to try making my own electic go-cart I would look at what people have done with PowerWheels Racing Series(PRS). That was a Maker Faire thing and lots of teams published their designs. IIRC 36V worked well and I think they sometimes used 2 500W motors or the fast ones did.

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What are you thinking about for motor controller? A soft start should be able to eliminate practically all shock load on the chain.

I agree, the cheap vendors don’t give you data, so it’s a bit of a gamble.

Different problem, but I converted my lawn tractor to electric, and it has somewhat similar weight though it probably doesn’t go quite as fast… I first used 4 Deka Intimidator 9A31 12V SLA batteries in series, and later replaced with 5 48V sections of lithium ion batteries from a totalled chevy volt in parallel. I used a 48V nominal Motenergy ME1004 permanent magnet DC motor that was a drop-in for the classic B&S ICE for the shaft, though the bolt pattern was different. It has no problem running the mower deck and tractor. Because this is a tractor with a belt CVT, I’m not using a motor controller at all, just a contactor.

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Hello, Michael! Thanks a lot for your time and your response. I haven’t made a decision about the controller yet. Despite the soft start that you mention, which would eliminate the shock load, as you said, the problem remains the same, I still can’t define what the starting torque of the motor is. Funny that you mention the Motenergy ME1004, because I’m actually trying to figure out the torque values of that same motor and other Motenergy ones hahaha I found it on an electric vehicle part components website ( Partes y Refacciones para Vehículos Eléctricos (energyev.com). It’s a mexican store. Even on this website, the data shown is very limited, I think.

Well, torque curves for PMDC motors will be almost flat over RPM until they rapidly fall off (which makes the no-load speed). You’ll get close enough from current at rated voltage times efficiency. (So for the ME1004 it’s 400A @ 48V * 88% efficiency peak; 200A @ 48V * 88% continuous; remember 1 VA is 1 Js.)

The reason you aren’t finding a lot on starting torque is that it’s not typically a limiting factor. And it definitely won’t be a factor for a go kart. If the kart goes, it will be able to start.

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