2 speed or dual sprocket centrifugal clutch on electric motor?

[ironosity]

Hey all! New to forum. I picked up a razer dune buggy for $40 bucks with the intention to upgrade for my 12/13 year old kids. I had a 36v 1000w motor I took off an electric minibike, and purchased a 36 v 16ah battery pack. When installing, felt it was a tight fit with the jack shaft so I took it off. If I remember right new motor has 12 or 13 tooth sprocket so slightly bigger than original 350watt motor. Also put 10" tires on rear. Anyways, between removing the jack shaft and upping gear ratio, the thing of course flies...once it gets going. Common problem right? Top speed or torque...choose one. Anyways, when thinking through my options to get some torque back, I came across dual sprocket centrifugal clutches that give 2 speeds on some minibikes. They seem to engage at around 2900 RPM.

My questions are:
1) Would it be possible to use one of these on an electric motor?
2) Would it achieve the goal of reintroducing low end torque, assuming the first gear was paired to a bigger axle sprocket) while maintaining topend speed?
3) Is there a better way (specific to electric motors) to achieve same goal short of simple getting a huge motor/controller that draws lots of amps?
4) Rather than just a rpm based clutch, is there something like this that can be engaged at will?

Before stumbling across this I was also toying with the idea of having 2 motors on same axle with different gearing, both with freewheel sprockets so that when not engaged, they would just spin freely, and then coming up with some way to switch power between the 2 motors as a way of changing gears. Not sure of the feasibility of something like this and it's an expensive experiment!

TIA! My goal is to learn on this one and then build out better one on a adult sized chassis (or start from scratch).

 

[EpsilonZero]

I have a dune buggy as well that I have modified and will likely be updating again since my oldest is getting bigger.

Electric motors output high torque from zero rpm and drop as back-EMF increases at higher rpm. A clutch or torque converter will reduce effective torque. You don't want that. Multiple motors, controllers, and gearing that spends time switched off just slow the kart down with dead weight, so you don't want that either.

If you want more torque, the correct answer is to upgrade your motor, controller, and battery to a combination that flows more current. Current is torque in an electric motor. Otherwise, changing your gearing to multiply what you have is an option at the cost of top speed.

If you want torque and speed, increase both your current and voltage in your proposed configuration. More voltage will spin a motor faster. Just make sure your components are rated to handle what you're trying to do.

 

[ironosity]

Electric motors output high torque from zero rpm and drop as back-EMF increases at higher rpm. A clutch or torque converter will reduce effective torque. You don't want that.

Would you explain this? It seems like the first engaged sprocket would be the same torque, since it would be engaged right away. And if geared for torque it would be significantly higher than current set up (geared for speeed). I get that the second sprocket would loose torque due to engageing at higher rpm (back-EMF) but since less torque is needed seems like less of a concern. And I'm sure there's some drag due to extra weight, resistance of non used chain and sprockets but doesn't seem like it'd be that much less. What am I missing?

Also, what set up do you have on your dune buggy and what do you plan to upgrade to?

Thanks!

 

[EpsilonZero]

When clutch begins to engage, it slips. It needs to engage far enough below your maximum rpm to engage fully, so you lose the increased torque at the top of your 1st gear. Whenever you're in that partial engagement band it will slip and heat up and you're losing the torque in that rpm region for your second gear. You would basically never be able to drive around at that speed without quickly destroying the clutch. How fast does the kart go now?

I have a 500w Currie over-volted to 36v with three Dakota Lithium LFP 12v 7Ah in series. I will probably weld a frame extension and mount my 51.2v RELiON 30Ah along with maybe a BOMA style motor and controller. I could throw on one of my Motenergy motors and a Kelly controller lying around, but I think that is even more overkill.

 

[ironosity]

Ok, I get it now. A clutch would be a horrible idea then since that middle ground is usually where they drive. Thanks for explaining! Top speed is around 24. Enough to keep up with his friend's 10x-the-cost ninebot gokart pro. you know...if his friend waits for him to catch up off the line Any suggestions for a motor/controller/battery combo that would make kart competitive with the ninebot without being overkill (or not competitive in the other direction)?

 

[EpsilonZero]

Switch to 48v and get a higher rated motor. You'll need a higher voltage battery that can also handle the current as well. I got a Currie motor and some other parts from electricscooterparts.com with no issues so I was considering buying the new stuff from them. They have appropriate 25mm sprockets for the stock drivetrain on the site, which is a plus if that's what you're running.

I was looking at these as potential parts...
#25 Sprockets
https://cart.electricscooterparts.com/48-volt-1800-watt-brushless-dc-motor
https://electricscooterparts.com/speedcontrollers48volt.html (1800w with reverse... out of stock)

Also, Functional Artist mostly deals with these smaller motors and has his own eBay supplier (alfa_wheels?) so he will probably have suggestions as well.

 

[journeyman846]

Also, Functional Artist mostly deals with these smaller motors and has his own eBay supplier (alfa_wheels?) so he will probably have suggestions as well.

Afla_wheels is who I actually got my 3000w motor and controller from, be careful though as the controller I received was not the controller listed. It did not have a good percent of the connectors and had no low/med/high speed settings.

 

[EpsilonZero]

Afla_wheels is who I actually got my 3000w motor and controller from, be careful though as the controller I received was not the controller listed. It did not have a good percent of the connectors and had no low/med/high speed settings.

These smaller motors and controllers always looked like a grab bag situation. I'd gladly pay a little more if it meant getting actual documentation and technical data.