Electric ATV As a Garden Cart Tractor and Utility Vehicle - a Power Wheelbarrow Alternative

I have steep hills and I wind up moving heavy materials around while gardening and improving my land. I was going to get a power wheelbarrow, but it just didn't seem like that much fun. What's better than a quiet little ATV that I can ride for fun and profit?

Supplies

For this conversion, I needed:

A used ATV. I chose a 110cc model and it just happened to be missing an engine!
A motor and controller. I wound up using a Vevor 2 KW brushless motor (that's 3 horsepower).
A battery. I probably went a little overboard with my 1KW/h pack (48v/20Ah), but it lasts for hours and I needed at least 30A continuous output.
A transmission to reduce RPMs. I used an ATV transmission with minor modifications. I'd recommend not using the one I got but getting a chainless version like this and buying an 11T sprocket for it separately.
A shaft coupler to connect the motor to the transmission. Note that this one was too big for the shaft, go for too small instead.
A bigger sprocket to reduce RPMs even further. The biggest I found was a 74T (transmission has 11T)

I also wound up adding some extras:

A battery box (I used a waterproof ammo can)
A new chain to match the sprockets
ATV style connectors
Some 48v light bulbs for headlights (No 12V components in this build)
A 48v tail/brake light (mine is 4-wire)
An Arduino (to make throttle response of the cheap controller more manageable)
Metal for a bucket holder or basket, and metal for a hitch.

I spent about $650 altogether on this build, not counting tools and shop supplies. I already had the garden cart.

Step 1: Decide on the Desired Performance and the Components

As you can see in the video, my ATV is able to pull about 300 lbs up an 11° slope if it's not too slippery. That's perfectly adequate for me. There are of course other questions, like:

Can you fit on a kid's ATV? If not, you might consider an adult model. They usually have differentials, and that will of course change the required drivetrain components, and may warrant a bigger powerplant.
What else will you use it for? Things like top speed come to mind, and that will decide what gear ratio you will be aiming for. Mine can do almost 10 mph at 1:21. I could have gotten more climbing torque out of it if I dropped the top speed and increased the ratio.
How hard will you use it? Perhaps you'll want to weld a stronger motor mount, reinforce the chassis, etc

You can also change the sprocket/chain type if you can find sprockets that will mount onto your transmission. I used T8F because that was the type of sprocket included with my motor and transmission.

Step 2: Disassemble Your Donor Vehicle

I was lucky enough to find a chassis without an engine, so I just needed to pull off the plastics and the controls. I had a choke control integrated with the brake, so I had to keep parts of that. Now is a good time to check the frame for cracks and repair (weld) any issues. Obviously you'll want to check the brakes, bearings, and so on.

The engine cut-off-switch and light controls will be useful in the build. I am using the cut-off switch as my reverse switch. Keep harnesses for these if you have them. I also kept my headlight harnesses and just replaced the bulbs with 48V.

Step 3: Install Your Drivetrain

My new rear sprocket had different mounting holes, so I drilled new holes in it in order to mount it on the existing hub. Once that's in place, you know where the chain will be, and thus where the transmission needs to sit.

Remove the bell clutch from the transmission. You may need to hold the output sprocket (I used a vice grip) in order to unbolt the clutch. Measure the shaft diameter (mine was about 9.6mm, and that was too small for the 10mm coupler). Check that you are getting a good fit on both shafts. You may need to shim the coupler. I notched my shaft coupler to allow it to close to 9.6mm, but that introduced eccentricity and I don't recommend doing this - shim it, epoxy it, weld it, whatever you need to do to keep it centered. If I had to do it over, I'd find a coupler that's too small and carefully enlarge the shaft opening by drilling or sanding.

Make a mount for the motor+transmission. I used a piece of plywood and a 2x4 (I drilled a hole in the 2x4 for the shaft coupler). The length of my coupler protruding past the transmission casing was exactly the thickness of the 2x4. so I just placed the wood between the motor and transmission.

I attached the plywood to the frame using some 1/2 EMT conduit straps, they fit my ATV frame size perfectly. If you're welding a mount, you're on your own.

Step 4: Reversing the Motor Direction

With my controller, the forward rotation was reverse for my motor orientation. You might be wondering why that would matter, since reverse is just a flip of a switch. It turns out that this controller limits reverse speed. In other words, forward is full speed, and reverse is very slow.

Normally, with a brushless motor, you can reverse motor direction by swapping any two of three wires (eg yellow and green in the above photo). However, this controller uses hall effect sensors in the motor as well, so you need to switch those wires too (the 6 pin connector). I assumed that colors of sensor wires would match the colors of motor wires, but they don't. I just kept switching them until the motor started working. You can sort of see that I had to switch green with blue for the sensor wires. Switching wires involved using a long needle to release the pins.

Step 5: Install Electrical Components

I mounted the battery inside an appropriately sized ammo can. It is padded in there with some foam. I used XT60 connectors and cable glands for the charge and output cables. The ammo can is mounted to the frame using 1/2" threaded rod pipe hangers. It was easier than welding and doesn't mess up the paint.

The controller on the Vevor kit has connectors for everything including a master on/off switch (which it comes with), and it has very low discharge rate (microamps) when off. Thus, it's fine to leave the battery permanently connected. The barrel style charge connector that comes with the battery/charger I bought was fragile and broke immediately, so I replaced it with an XT60 (after a lot of fireworks, as there is no way to turn the battery off).

I used every connector on the controller except for the charger port (battery has one), second brake switch (see below) and 3-speed (I used an Arduino to limit speed instead, see below)

As I mentioned, I'm using the original engine-off switch as my reverse switch. I also used some of the original ATV harnesses to make a new harness for the headlights (keeping the original headlight switch). Since my bulbs are 48V, I just connect the headlight switch to the "indicator" connector on the controller, and the switch controls both headlights and taillight.

I decided to connect the brake switch on the front brake but not the rear to the controller. This allows me to start on a hill while holding the rear brake (otherwise, the controller would refuse to operate).

I used the ATV connectors to make a harness for the brake/tail light and the headlights.

Step 6: Hitch

Use some spare junk to make a hitch. I used an exhaust clamp and an eyebolt. With the large size eyebolt, I can use both the garden cart hitch pin and a normal tow ball for full sized trailers. The downside is that there is a lot of movement when using the small (3/8") hitch pin, but you could make a rubber plug that snaps into the eyebolt and absorbs some of the movement.

Step 7: Optional: Bucket Holder

What I really wanted was to add a big, removable basket to either the front or rear of the ATV. In the end, I didn't find a basket I liked, so I made a bucket holder. I bent some 1/2" rebar with pipes and lots of brute force, reused steel pipes from an old camping chair (if you smash the ends of thinwall pipes closed, you can make very nice ends for bolt mounting). I assembled and welded the metal parts together around a bucket (which melted in the process). The shape is perfect for a bucket, but it turned out a bit crooked.

Step 8: Optional: Throttle Smoothing

With the cheap Vevor controller, having that much power and torque resulted in very jerky user experience. I needed to make the throttle response slower, and I went through a bunch of analog circuits before giving up and writing some code for an Arduino.

I had a 5 volt Pro Micro laying around so I just put it in between the throttle and the controller. It is powered by the (almost) 5 volt output of the controller and does the job. You can find all the details here. Waterproofing the Arduino is a bit of a TODO, I just wrapped it in fusible tape for now and it's under the plastics.

I also tasked the Arduino with enforcing an adjustable speed limit. To that end, I added a knob (placed where the gas cap used to be) that allows me to set maximum speed as low as 0.5 mph, useful for fine maneuvering in tight spaces and teaching kids to ride it. I made the knob using a potentiometer (1K), a piece of thick plastic from a motor oil bottle, and some rubber foot that I hot-glued onto the shaft. The piece of plastic is sized to the gas cap recess and hot-glued in place.

I'm pretty happy with how that part turned out.

Step 9: Test It!

Tow something ridiculous with it like I did!

OK, you may want to start with a gentle test - on my first run I realized that I never closed the master link of my chain. I also found that my front (mechanical drum) brakes are fairly ineffective, so I added a hydraulic disc brake on the rear axle, which works great. They both have "parking brake" features which are very helpful.

Step 10: Conclusions: the Pros and the Cons

Pros

The ATV is very fun to drive.
It's quiet and always ready to work. I don't have to start it.
It's light enough to lift and reposition by hand in tight spaces.
It's definitely fast enough and strong enough.
I think it's pretty useful for moving stuff around the yard or even a larger estate.

Cons

You need a place to store the ATV and the cart instead of just one power wheelbarrow.
The turning radius is huge because there is no differential. so there are a lot of 3-point turns involved when maneuvering in tight spaces (but you can just lift the back and move it). Steering authority is also limited on slippery terrain.
It's 2-wheel-drive, so traction can be a problem on steep and slippery hills.
Backing up with my Gorilla cart is basically impossible, and I wind up having to unhook the cart to back it up.
Of course backing up would be easier with a single-axle cart.

All complaining aside, I love having a quiet, low maintenance utility vehicle that fits in tight spaces and puts a smile on my face.