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Discussion Starter · #1 ·
Hi Everyone,

My 10-yr old girl wanted to build an electric car, and so we did. It's about the size of 2 power wheels, lightweight with PVC pipe and some wood framing for support. We have everything except the motor. I bought 2 power wheel motors, 24volt each at 30000rpms, 4 12v batteries, and a 24v wiring harness. We attached the motors to the rear wheels, and tested 1 of them by hooking 2 of the 12v batteries in series to 1 of the 24v motors through the 24v motor controller. The car was up on "jacks" when we tested it. The wheel spun great for about 30 seconds, then the motor smoked and started to flame a bit. I'm no engineer or mechanic, just a mom. Can anyone tell me what I'm doing wrong? My little peanut is really bummed. Any advice will be appreciated.:(
 

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Discussion Starter · #3 ·

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That needs to be severely geared down. If you direct drive it, it'll suck so much current from the loading on it that it lets the magic smoke out. Even up on blocks the friction & inertia is too much load.

Wheelchair motor? Or pull the motor/gearbox out of a craigslist Barbie Jeep, or similar, junker. Last option is a train of pulleys. Another option could be a window motor from a car if you can figure out how to couple it to your axle.

There's also a geartrain the Hobby Shops sell that has reduction. You probably want something around 500:1

Edit: forgot to mention. Volts give you speed, current gives you torque. Going to 24V from 12V for a heavier car without a speed reduction gearbox is pointless.
 

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Discussion Starter · #7 ·
@Electric Land Cruiser, I do! Attaching pics:

Front of car - bumper, hood and dash are not on yet:
Tire Wheel Vehicle Automotive tire Road surface


Side View - doors not permanently attached yet:
Wheel Tire Plant Automotive tire Vehicle


W/ the Peanut for scale:
Wheel Tire Plant Vehicle Automotive tire


Rear View - trunk lid will be covered:
Tire Wheel Vehicle Automotive tire Tread


Close up of one 24v motor with its two 12v batteries, with the 24v wiring harness and controller. I disconnected everything after the motor started flaming. The motor is attached to the wheel underneath using a flexible coupling adapter, then bolted to the wood.
Tire Automotive tire Tread Wheel Electrical wiring
 

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I can see the problem now! Thanks for the photos. Your craftmanship is good! The cart looks well built, nice job.

The motor is for a small toy car, not a car to carry a person. That is why it burnt up. It was overloaded even just turning the wheel.

Do you have a link for the motor controller that you purchased? It looks appropriate for the vehicle from the photos.

This motor and controller is more appropriately sized for this project. Also you could try to find a Razor E300 scooter locally on Craigslist or similar for cheaper.

 

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Discussion Starter · #10 ·

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You've done some very nice work! ;)
(1) 24V 500W motor should propel that size of a kart nicely
...& you only need the (2) 12V batteries
... or you could use all (4) batteries for an extended "ride time"

Here is a video of a small kart I built for my son ~5 years ago
...it has a 24V 500W motor
...& (2) 12V 12AH SLA batteries

It moves right along
...& the ride time was ~30 minutes
 

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Discussion Starter · #12 ·
Those are amazing! Welding is so next level, lol. Love the colors, and your boys look so happy! Thanks for the advice. I'm feeling much more confident about the next steps.
 

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Are you using the gear reduction gear box that goes with this motor?: https://www.amazon.com/18000RPM-Gea...b98a6&pd_rd_wg=NGbj6&pd_rd_i=B07T572NXL&psc=1
Although from the product reviews, it looks like this gear box is too light duty and prone to failure.

The 500W motor is one option. But it will need a bigger controller, a chain drive set-up, and probably overpower the car, making it too fast for safe driving!
 

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Discussion Starter · #14 ·
I love all you guys. I was pretty excited about the 500w motor, but after thinking about it I agree with @electro wrks that it would be too much power for my lightweight contraption. Might send the Peanut flying.

So, @remy_martian says it needs to be geared down, and @electro wrks asks if I'm using a gearbox and now I feel reaaally stupid because I wasn't using any gear reducer. Would a planetary gear motor solve the problem??

Now I'm back to not knowing what rpms, watts and all that. Any thoughts? Here's one on amazon: High Torque 24v 12v Dc Planetary Gear Motor - - Amazon.com
 

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For peanut, 15mph or about 20 feet/sec (1200 feet per minute) is plenty of speed, especially with a PVC frame.

Nobody said there wouldn't be math:

RPM = ~400/(tire diameter in feet)

For 7.5MPH, RPM = ~200/(tire diameter in feet)

The HP & torque needed is more complicated but I'd aim for RPM between the range of the two.

Take a look at Functional Artist's 3 wheeler, recently posted. 1 HP gets you about 15 mph. So, half a horse in total (1 horse is 746W, so 1/2 horse or so, 378W is ballpark...30A motor on 12V) should be plenty on a gearbox that gets you close to the 7.5MPH RPM, calculated above

One thing you could cobble up is a battery powered hand drill, which has the gear reducer in it
 
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