Picking an electric motor/engine

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amaraone

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Hi forum members, my name is amaraone. First off I would like to say thanks for reading this post as it is my first one. Let me explain what's going on with my go kart here;
So me and my friend had the idea to make the most badass go kart possible; we have a company that is going to be making a body out of carbon fiber that way the go kart is extremely light. The one thing is, we want to make it electric due to safety concerns with my mother. We are trying to get the Go Kart to top off at 50 MPH with one engine but I'm not sure what to use, any suggestions would be appreciated. Our budget for the engine is a maximum of $700 USD, once again any help would be greatly appreciated.
 
OzFab

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What are your mothers safety concerns?

50mph is a massive speed for a gokart, that's beyond some racing karts; at that speed, EVERYTHING will need to be dialled in to within a millimetre or DEATH may occur...

The main difference between dino fuel engines & electric is torque response; with a dino fuel engine torque builds up as the RPM increases, with an electric motor, torque is instant & constant, only the RPM varies...

There's a few factors to calculate before considering any motor; first, you need to calculate what gear ratio is requires to reach the desired speed; this includes tyre height; using the same sprockets, 10" tyres will produce a different drive ratio than 20" tyres...

When calculating the drive ratio you also need to know the max RPM of the motor... this is where it gets difficult because it's a catch 22...

Also consider that the higher the voltage, the higher the torque; a 500w 24v motor will deliver around double the torque of a 500w 12v motor... & so on for higher voltages (36v, 48v); then you have another catch 22 because, the more voltage required, the more batteries you need & batteries are heavy... & expensive... Have you included wiring, batteries, controller, etc into your budget?
 
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amaraone

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Fabroman said:
What are your mothers safety concerns?

50mph is a massive speed for a gokart, that's beyond some racing karts; at that speed, EVERYTHING will need to be dialled in to within a millimetre or DEATH may occur...

The main difference between dino fuel engines & electric is torque response; with a dino fuel engine torque builds up as the RPM increases, with an electric motor, torque is instant & constant, only the RPM varies...

There's a few factors to calculate before considering any motor; first, you need to calculate what gear ratio is requires to reach the desired speed; this includes tyre height; using the same sprockets, 10" tyres will produce a different drive ratio than 20" tyres...

When calculating the drive ratio you also need to know the max RPM of the motor... this is where it gets difficult because it's a catch 22...

Also consider that the higher the voltage, the higher the torque; a 500w 24v motor will deliver around double the torque of a 500w 12v motor... & so on for higher voltages (36v, 48v); then you have another catch 22 because, the more voltage required, the more batteries you need & batteries are heavy... & expensive... Have you included wiring, batteries, controller, etc into your budget?
Click to expand...

When you say 50MPH is a "massive speed" for a go kart, what's the regular speed that they should go at? The go kart we are designing is for professional racing basically. But again as you say this, what would be the normal speed of a Go Kart; I've seen some go 30-40 MPH; would that be better?

And to clarify, my mothers safety concerns are the engine blowing on us and the fact that is gas and it could blow up.

And yes we have added that to our budget, we have $700 specifically for the engine and the controller.
 
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If I were your mother, I would be more concerned about you guys going 50 in a kart that you guys made. Race karts are professionally made and are made to handle the speeds and stresses that it experiences going at fast speeds.

A lot of race tracks will not even allow homemade karts onto the track.
 
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amaraone

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landuse said:
If I were your mother, I would be more concerned about you guys going 50 in a kart that you guys made. Race karts are professionally made and are made to handle the speeds and stresses that it experiences going at fast speeds.

A lot of race tracks will not even allow homemade karts onto the track.
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Yea just to clarify my friend was the one who wanted this speed, I always told him 30 MPH. He said if I could find an engine that would go 80MPh, but I directed him to this forum post and he understand we can't go that fast. Thanks for telling me this though.
 
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If your mother is worried about gasoline, you can use a fuel cell designed for racing - they are extremely safe. For example: http://www.summitracing.com/parts/sum-290110/overview/

Right now, the bang for the buck with electric drivetrains isn't nearly as good as gasoline engines. If you want to go even 30 mph for any length of time, you'll need to spend thousands on an electric drive train (batteries, motor, controller, liquid cooling, etc).
 
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Zombient

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I don't think you understand how fast 50mph is on a go kart, but here's how you can get a feel for it.

Have your friend drive down the highway, open the door, and stick your head about 2 feet above the pavement. Seems a whole lot faster now, doesn't it? These karts are 100% analog/manual. There's no power steering, no shocks (usually), no traction control, no power brakes, etc.

Landuse is right, the "racing karts" use a lot of math and calculations. They're specifically designed for one use. I'm not saying you can't do it; I don't know your engineering background.

A wreck at 50mph, you're going to need a lot more than just a helmet to survive that.

https://www.youtube.com/watch?v=xxnvJ3cpkOg
 
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Kinetic energy is proportional to velocity squared, which is why you may have heard the phrase "speed kills". If you want to fast on the asphalt, you should wear body armor & a full protection helmet. Also, you need to have good tires (rated for speed), and good brakes.

You can have a lot of fun driving off-road at a much slower speed. Also, driving a go kart on the public roads is illegal.
 
OzFab

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I've been driving for many years &, inside the enclosed cabin of a vehicle that has had countless hours & dollars of R&D, 30mph seems very slow but, trust me, when your butt is 2-4" from the hard pavement & there's nothing around you, 30mph feels pretty darn quick...

As I mentioned earlier, the major difference between gas & electric is torque delivery; most members industrial engine powered karts have a top speed of ~30mph & there's a very good reason for that...

To make the best use of the available torque, the drive ratio is highly considered &, to obtain the best possible acceleration, top speed must be sacrificed...

What does that mean? Well, there's lots of math involved but, to make it simple, a certain amount of leverage is needed to make an object move; the more leverage needed, the slower it will move...

Now, in relevant terms, If a 6:1 gear ratio is needed to make a kart move without destroying the clutch, top speed will be determined by that same ratio as the engine will, at some point, stop increasing in RPM; by changing the gear ratio to increase top speed, you risk damaging the clutch & not moving at all...

That all applies to a gasoline engine, the same rules do not apply to electric; of course, some thought need to be given to gearing but, an electric powered vehicle may be geared higher than a gas powered vehicle, therefore, reaching a higher top speed without placing too much stress on the motor...

Unfortunately, your best ally here (itsid) is MIA; apart from the necessary knowledge you seek, he has a formula for converting the potential hp of a gas engine to the required potential hp of an electric engine; it's a real eye opener...
 
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