1 motor vs 2 motors electric go kart

Thread Starter

Donsa

Joined Sep 19, 2018
5
I am in the process of building an electric go kart, and I came across the expenses associated with such a build. I noticed that motors in the 4kw range are pretty expensive. My only option for keeping the price down would be to get 2 - 1.8kw dc brushless motors instead (about half the price, even though it does not reach 4kw, pretty close).

This is the motor in question: https://www.ebay.com/itm/1800W-48V-...AOSw011blk6z:sc:FedExHomeDelivery!78641!US!-1

At this point, my questions are as follows:

1)Would using 2 motors be a good idea? I imagine one motor spinning slightly faster, or one starting to spin before the other, creating some kind of damage from unmatched rotation; am I wrong in thinking that?

2) Would 2-1.8kw motors give me more speed over just 1 of them? In that case, how? Again, I imagine them spinning at the same speed, so no gain there; maybe the torque would double? How would that contribute to increased top speed?

3) If using 2 motors for the 2 back wheels is plausible, should I use a single axle with both motors connected, or should I give each wheel its own little axle? Why?

On a side note, all replys are welcome, but please try to answer the post questions in your comment (to avoid more confusion).

Thanks for taking the time to answer!
 

Thread Starter

Donsa

Joined Sep 19, 2018
5
What is your voltage source? Do you have 48 volts available, or what specifically?
Yes, I will use 18650s because I can get them cheap enough, dont wanna go with lead acid because of the c rating. I will specifically use lg he4 (3.7v 2.5 Ah), here are the info https://www.imrbatteries.com/lg-he4-18650-2500mah-20a-flat-top-battery/ . 13s15p will give 48v and 37.5amps, enough to run both motors for about 30 mins ( i can always add more batteries for peak currents/longer time).
 

drc_567

Joined Dec 29, 2008
1,093
The rpm that a motor rotates at depends on the load torque that it is given ... the torque at the track surface. Two identical motors, seeing the same rear wheel torque, should have the same rotational speed, or nearly so.

For two identical motors, a single bar axle should work, with both motors attached. This should allow a uniform rpm between the two motors. Two separate axles could cause separate motor rpms, creating problems of some sort.

The performance number that you are looking for is the total torque that reaches the rear wheels ... so two of those motors might work nearly as well as the 4kw motor. If the rear-end torque is too much, the wheels won't grip at take-off and you will have to increase the downward load over the rear wheels ... add extra weight ... or change the sprocket ratio.

If two motors, in a parallel arrangement, test out with no problems, try 3 motors in parallel.
 

Thread Starter

Donsa

Joined Sep 19, 2018
5
The rpm that a motor rotates at depends on the load torque that it is given ... the torque at the track surface. Two identical motors, seeing the same rear wheel torque, should have the same rotational speed, or nearly so.

For two identical motors, a single bar axle should work, with both motors attached. This should allow a uniform rpm between the two motors. Two separate axles could cause separate motor rpms, creating problems of some sort.

The performance number that you are looking for is the total torque that reaches the rear wheels ... so two of those motors might work nearly as well as the 4kw motor. If the rear-end torque is too much, the wheels won't grip at take-off and you will have to increase the downward load over the rear wheels ... add extra weight ... or change the sprocket ratio.

If two motors, in a parallel arrangement, test out with no problems, try 3 motors in parallel.

Hey thanks a lot, this is precisely the answer I was looking for. For the torque, I was just worrying about getting enough; if I have more torque than needed, I could just lower the rpm, so to let the wheel get a grip of the ground, right? It seems to me that very low rpm offers more torque for less speed, and gives time for the tire to adapt.

Btw I will probably try a 3rd motor later on, having seen the big 10kw motors on go karts, looks fun ;)
 

drc_567

Joined Dec 29, 2008
1,093
Sensacell has a point about cornering with a fixed axle. The two rear wheels normally turn at different speeds when going around a sharp corner ... outer faster, inner slower. With a fixed axle, they can only turn at one speed. So you can either slow down at corners or slide around.
... Not sure if this is a concern with karts or not.
 

jpanhalt

Joined Jan 18, 2008
11,088
Agree with Sensacell. My car has a differential in back to allow the wheels to turn at different speeds. That good, not bad.

Conceivably, with 2 electric motors, you could make a electronic differential.
 

shortbus

Joined Sep 30, 2009
8,469
Use two motors - one on each wheel.

Then you don't need a differential!
Don't know about how they do it now but when a teenager many of us had go karts and one friend even raced his in competition. They all had a solid rear axle with both wheels attached to it and the engine. Even when using two engines. A kart turns like the "Drift cars" of today, the wheel that would turn slower with a differential just spins when in a turn, loses grip with the surface of the ground..
 

dendad

Joined Feb 20, 2016
3,811
My Dad's racing kart has 2 motors, one for eack back wheel. No live axel. It went really well. A live axel can work ok, but I would vote for one motor for each back wheel.
Then, as an extra programming excercise, monitor the motor speeds and limit the drive to the motor that spins significantly faster than the other. A Limited Slip Diff :)
So then if a wheel comes off the ground, it does no spin up.
 

shortbus

Joined Sep 30, 2009
8,469
@ dendad, I haven't been around karts since late 1960's my description as I said was how it used to be done. The last one had a Villers cycle engine with solid axle. It was in the same racing class as the two engine McCulloch engine karts, again with solid axle.
 

dendad

Joined Feb 20, 2016
3,811
I haven't been around karts since late 1960's my description as I said was how it used to be done. The last one had a Villers cycle engine with solid axle. It was in the same racing class as the two engine McCulloch engine karts, again with solid axle.
That sounds like my Dad's kart era.
His had twin Whirlwind engines and the karts with the McCulloch motors just disappeared into the distance in front. They really flew!
I was young so was only allowed to drive it with one chain removed so only one motor was running. Except one time when we ran it on a rough paddock. The ground was so bumpy, one motor was not enough, so the second one was engaged. I remember rattling around on the seat that much it was hard to keep my foot on the accelerator. But, boy, did it have some kick when I floored it!
We were involved in building an amateur race track in the bush, but just as it got almost done, the area was taken over to build a large dam for domestic water supply, and no access was allowed. That killed the gokart club.
 

shortbus

Joined Sep 30, 2009
8,469
They actually had paved, small tracks in my area just for kart racing, back in those days. The tracks were ~1/8 mile if I remember right. There was a circuit of tracks that held weekly races just like the big circle track guys. Some of those Mac motors had as many as 3 carbs on them and ran like a raped ape! They were the most winning motors available. Don't know why kart racing ever went away?
 
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