What determines motor RPM?

[GearheadMachinist]

I have a Cushman Titan industrial cart. I want to make it go 30 mph.

I can't gear it up with tires, there's no space. It has a unique transaxle that doesn't take gear sets that are available. So, the way I see it, I can either get a faster motor, and/or build a pulley and jackshaft arrangement to increase the speed to the axle.

So, to my question. What determines the max speed of a DC motor? I was going to put a Motenergy ME1003 in it and run it at 72 volts, 400 amps, but everywhere I look lists a different number for the motors RPM. If I could get it to spin 10,000, I wouldn't have to bother with the pulley thing. Is that possible?

[bronsonj]

Most of the motors used in electric carts (both utility carts and golf carts) are safe generally to 6000 rpm. They do have motors you can get with High Speed Banding that can safely exceed 6k and still live a long life. But you are likely getting nowhere near the motor max. Increasing voltage, reducing drag can both increase motor rpm. reducing drag is mainly maintenance items (checking brake drag, insuring tire inflation, checking front end alignment) and can gain you 2 or 3 mph. Increasing voltage can wake up your cart. If your stock controller is 36/48v compatible it may be reasonably priced too.

What voltage is your industrial cart? I assume it is a series cart. A picture of the cart, controller and motor would help.

My buddy has a Taylor Dunn airport cart. It's electric 36V. We converted his to lithium with an 11 cell pack (3P11S, 141 amp hours). We designed it so he can still use his stock lead acid charger. The results are much more energetic acceleration and his top speed went from 12mph to 15/16mph and now he charges the cart once every 2 or 3 months. His controller is not 48v compatible, but on the lithium pack he maxes out at 43v (or so). Since his controller wasn't compatible with higher voltages we were limited to what we could do.

I went 58v lithium and changed my controller on my golf cart and my top speed went from 19mph (at 48v stock) to 34 (at 58v with an Alltrax controller).

If you want 30, we need to know where you are starting from. Also know that these carts are designed for 12 to 19mph. My cart will do 34, but I tuned back the controller to keep it to 30 or less because the steering gets scary at 30.

[izzybird]

Originally Posted by bronsonj

My buddy has a Taylor Dunn airport cart. It's electric 36V. We converted his to lithium with an 11 cell pack (3P11S, 141 amp hours). We designed it so he can still use his stock lead acid charger. The results are much more energetic acceleration and his top speed went from 12mph to 15/16mph and now he charges the cart once every 2 or 3 months. His controller is not 48v compatible, but on the lithium pack he maxes out at 43v (or so). Since his controller wasn't compatible with higher voltages we were limited to what we could do.

Sorry to derail.
What controller does he have, if you don’t mind me asking? I thought the old Curtis controllers should be good to about 60v and the Sevcon to about 70v. I think the Sevcon micropak 24-36v is only rated to about 50v.

[bronsonj]

Originally Posted by izzybird

I thought the old Curtis controllers should be good to about 60v

Wow, 60v! His is a 400amp controller, I know that for sure and I'm 90% positive it was a curtis. He really didn't want to let the magic smoke out of any components, so we opted to keep using the stock charger under the assumption that whatever the stock charger put out the stock controller could handle. That's how we ended up where we are at. He "says" he doesn't want more speed, but if the controller will handle 60v...

[cricketo]

Originally Posted by GearheadMachinist

So, to my question. What determines the max speed of a DC motor? I was going to put a Motenergy ME1003 in it and run it at 72 volts, 400 amps, but everywhere I look lists a different number for the motors RPM. If I could get it to spin 10,000, I wouldn't have to bother with the pulley thing. Is that possible?

ME1003 will change RPM based on the voltage. It is reported to have 3700RPM at 72V uloaded (!!!!). Not only you can't get it to run at 10,000 due to mechanical and electrical limitations, but also you can't run it at 400A continuously either - it is only rated for 200A. Additionally a thing to remember it is a Permanent Magnet motor, and rare-earth magnets used there are sensitive to heat, you can demagnetize them by letting the motor overheat.

With that in mind, you probably want to have intermediate gearing from the motor to transaxle, that way you can safely increase the output RPMs without overdriving the motor.

[GearheadMachinist]

It's a 36 volt cart, stock. It has the old resistive coil type speed control. I overvolted it to 48 and got a few mph, then went to 72 and got a few more, but obviously that's hairy and gonna blow stuff up.

I've bought the ME1003, and I've decided that I need to build a jackshaft assembly to increase the RPM to the axle. Kind of sucks, but hey, what can you do?

[cricketo]

Originally Posted by GearheadMachinist

It's a 36 volt cart, stock. It has the old resistive coil type speed control. I overvolted it to 48 and got a few mph, then went to 72 and got a few more, but obviously that's hairy and gonna blow stuff up.

I've bought the ME1003, and I've decided that I need to build a jackshaft assembly to increase the RPM to the axle. Kind of sucks, but hey, what can you do?

Well, if you want to do that in a controllable fashion, you want to put a temp sensor on that motor and also a tachometer. Don't go above 6000RPM as discussed, and don't let the temp to raise too much.

https://www.plantengineering.com/art...ow-hot-is-hot/

[bronsonj]

it'll be interesting to see how the ME1003 handles the load of a cart with a jackshaft in there to gear it up. Another option is to mate a golf cart rear end in there instead. Golf Cart rear diffs are geared to 12.44:1 but you can get other gear sets. You can probably get a series wound rear diff with a motor on it fairly cheaply.