Attempting to convert CFMoto gas UTV to electric.

[WCRiot]

Hey guys
I haven’t posted before because I have been searching and reading about a lot of other projects.

I purchased an older gas powered CFmoto UTV to convert to electric drive. I wanted 4wd and a dump bed. When I purchased it, I didn’t know the transmission/transfercase was built into the engine block. I wanted to ditch the engine and connect an electric motor directly to the transmission.

I have now stripped the engine and using it as a case for the transmission and such parts. I’m not sure if this is the ideal setup which is what brings me here with questions.

First question: What gear ratio do most of you use? I need to go 30-40mph, and move an 800lbs (without batteries and other electric drivetrain parts) buggy. I roughly calculated that the current transmission is about 3.75:1. That does not include the front and rear differentials (which I don’t think will change the ratio too much more).

Second, what motor/controller setup would you recommend for this application?

Third, has anyone ever used a worm drive gearbox in their carts? These things don’t seem to be designed for “high” rpms. When I say high, these gearboxes seem to be built for 50rpm and less.

I realize this build is probably a bad idea. But before I give up I wanted to reach out to everyone on here and get some advice on how to get things cart moving again.

Here are some pictures of my terrible idea from the day i got it. I'm working on prettying it up. I will share those pictures when completed.

[WCRiot]

When i saw the engine transmission complication i started to look at dual output shaft electric motors. There aren't many options out there and more importantly a design like my sketch below only had the gear reduction of the differentials. So probably unrealistic

[WCRiot]

A third option assuming i insist to keep 4wd.
I could put two electric motors, one for the front and one for the back. I would need some sort of gear reduction mechanism that they would attached to before going to the driveshafts.
That would add weight, limit the controller options and increase cost.

But I'm hoping some forum members have better ideas or have some products they can refer me to.

[bronsonj]

Heck of a project!

I can't see your sketches or photos because most hosting sites are blocked by my employer so I can't help with that.

As far as speed goes, 35+mph is doable but is dramatically affected by your gearing. I'd go with an AC motor and controller. Navitas sells kits for that. The AC motors seem to have a higher max safe RPM. I guess they're banded to protect them from the centripetal forces.

To calculate speed you'll need to know the differential gear ratio and the tire diameter. You already know the transmission gear reduction. Then you can calculate the distance traveled in inches per revolution of the engine. Or you can see how many engine revolutions are required to rotate the tires one time and extrapolate. You know the length of a mile is 5,280 feet so you can calculate how many revolutions are required to travel that mile and divide by your max motor RPM.

[WCRiot]

I measured the gear ratio of the front and rear diffs.
I'm getting 3.75:1 maybe more like 4:1

So if i used the transmission from the gas engine that is 3.75 + the diff which is 4. That gives 7.75:1
From what I read on here, that is too low. I was told all in i want to be around 15:1

Bronsonj. Thanks for helping with the calculation method. I might try that.
I like the Navitas kits but form what i say they are rated to 5kW max. Is that gonna be enough?

My next challenge is those Worm Gearbox that i would like to use to ease the install. Those are not typically rated for 6krpm. Which the electric motors have a max rpm of about 5700.

So now i need to figure out. What rpm will i typically be spinning? This would help determine if i use the worm drive gearbox or not.

[bronsonj]

golf cart motors in stock form are often limited with a stock controller to around 3600rpm. With an aftermarket controller we open them up to around 6,000 rpm. Beyond that you risk the motor coming apart internally, which never ends well. AC motors seem to have high speed banding in them and many AC motors are capable of 10k rpm...

But my DC motor in my current cart is perfect for me. I had it set to 5700 rpm limit but dialed it back because that was too fast for me.

As for final drive ratio, most EZGO carts are 11.44 to 1. I just use 12:1 for my calculations and it works out well. Some EZGO carts have lower gears from the factory and you can get aftermarket gears as well.

My Alltrax is 360 amp max but in real world use I've never seen it more than a smidge over 300 amps for a brief moment (that was a wheelie...). Running at a continuous 23/24mph on flat pavement draws about 70 amps at around 54V. That's 3,780 watts continuous. I've seen brief spikes to 300 amps from a dead stop mashing it to the floor with an aggressive acceleration curve programmed into the controller, but 300 amps at 54v is just over 16,000 watts. So I'm wondering if the 5kw rating is the continuous rating?

If you are using 48v then 5kw means you're pushing only 104 amps. Lots of people run Navitas controllers so I'm just wondering if 5kw is not the peak rating???

Also, aren't worm drive gearboxes inherently inefficient? On an electric cart/utv efficiency is quite important.

[WCRiot]

Originally Posted by bronsonj

If you are using 48v then 5kw means you're pushing only 104 amps. Lots of people run Navitas controllers so I'm just wondering if 5kw is not the peak rating???

Do you really mean peak? Because i agree 104Amps is low. Maybe the 5kW rating is continuous and more of a cruise mode. Because the controllers are called 440A or 600Amp controllers. I'd like to think that rating refers to to the peak. But i don't know for sure.

Originally Posted by bronsonj

Also, aren't worm drive gearboxes inherently inefficient? On an electric cart/utv efficiency is quite important.

No clue. I never heard that. They are only two gears so that's hard to comprehend. I do know they are NOT designed for high rpm. That is my biggest challenge. Finding something that can handle 5k rpm+

[WCRiot]

So as an update.
I am ditching the worm gear drive idea. My plan is to pull the bevel gear/driveshaft assy out of the house. I will use that to retain the 4wd setup.

I will likely ditch the bevel gear and install a Sprocket type gear to that shaft. I'm likely just going to make this thin chain drive which will allow me to change gear ratios so much easier.
There is a small possibility that i will retain the bevel gear and get a pinion gear to mate with it. The current pinion is too large to help with the ratio.

[DaveTM]

So, if I understand this right, you want to mount an electric motor for the front, and then another for the back, and connect the "drive" from an electric motor to a gear\sprocket that you will attach to the pinion and using a chain to go from the electric motor to the existing pinion(s).

Here is my very crude drawing...of just one axle. Is this the thinking?

[WCRiot]

I've been bouncing between ideas. But have decided to go with a simpler more typical design. See attached crude sketch.

Basically just going to add a large gear to the coupling drive shaft that i removed from the CFMoto gas engine. I will then have a small gear on the electric motor. Everything driven by a motorcycle chain.

This makes it much easier for me to change gear ratios if needed to get more speed or more torque.

So i need to decide on gear ratio. then electric motor/controller combo.
Tires are 24inch. Gear ratio of differentials is 4:1 with these tires. So the gear ratio at the motor probably needs to be close to 10:1

It sounds like most golf carts are running around 15:1

I looked up the Hunt VE cart. That seems to be running a72V system. That's higher than i was thinking. But i wouldn't say it's unreasonable.