Building an Electric Wagon

[bj2386]

Hi all,

I am unsure if this is the best place to discuss this topic, but this forum seems semi-appropriate so I'll give it a shot.

I am currently in the process of designing a battery-powered yard wagon to be used for hauling loads around a homeowner's property. The goal of this wagon is to replace a gas-powered lawn tractor (mower) + small trailer combo which is presently being employed. This lawn tractor is not used for mowing at all, meaning it is simply adapted as an engine for towing the small trailer.

I see two main negatives for this current setup:

1. Lawn Tractor + Trailer combo occupies a large amount of space when stored
2. Using the trailer oftentimes requires a decent number of tractor "start-stop" cycles (fill the wagon, crank tractor, move short distance, turn tractor off, unload wagon, crank tractor, move short distance, turn tractor off, repeat), which seems hard on the engine at times

In my mind, a useful solution is to put an "engine" in the wagon itself and make it electrified to better handle the previously described use case. Hence the impetus behind the design I'll describe below.

The wagon currently being used is the following: Yard Cart. The size and weight capacity of this wagon is good, so I would like the new self-powered version to mimic it in that regard.

The graphics below are some basic mockups of what what I am envisioning the final product will resemble.





The frame will be made from square tube. Sitting on top of the frame is the haul bed and the electrical components up front. I anticipate having a battery box with (3) 12V sealed lead acid batteries (wired in series) and a controller box containing this card: Motor Controller. This controller will be used to drive two 36V electric motors of the following type: Electric Motor. These motors are geared down to maximize torque and lessen the speed (the wagon should never have to travel faster than a brisk walk, IMO).

When it comes to steering, it seems the easiest approach is to adopt a differential drive (skid steer) configuration. This requires each engine to drive each side of the cart independently.

Another decision to make the build easier is to have the wagon controlled by an RC remote, rather than designing/building a set of hands-on controls for the operator. I am sure there will be some benefits in being able to move the cart at a distance as well.

These are the high-level design choices I have made thus far. Further details will be added as I progress through the build process. BTW, some of my implementation will be based upon a set of videos I stumbled across on Youtube: https://www.youtube.com/@giterbilt5146/videos. This gentleman upgraded his push lawn mower to be remote-controlled and his discussions of electrical components and their arrangement seems very relevant to aspects of my project.

If folks have any questions or suggestions, please do not hesitate to post them!

 

[Denny]

I would find an old hydrostatic drive from a junked tractor and only use 1 motor. It will need to be from a golf kart or something similar. Using 2 motors the needed amperage would be through the roof.

 

[Rat]

There's a simple way to bake a chain driven differential that can be adapted for pretty much any axle.

Split the axle precisely where you want the drive to be.
Add a pair of pillow blocks for the cut ends.

Add on couple retainer collars to eliminate axle slide out.

Then you need 2 freewheel thread adapters (kinda like for an adult trike) 2 freewheel sprags, and whatever sprocket size you intend to use.

You may or may not need spacers, but you use bolts to make a sandwich of the gears making sure to keep the freewheels properly oriented as RHD.

What this accomplishes is both wheels get driving power regardless of how much slip is encountered, but the wheel on the outside of a turn can freewheel to overtake the inside wheel without ever having consequential power loss.

 

[bj2386]

I would find an old hydrostatic drive from a junked tractor and only use 1 motor. It will need to be from a golf kart or something similar. Using 2 motors the needed amperage would be through the roof.

Not sure if you looked at the link I provided above, but the motors I have tentatively decided upon are 1HP 800w brushed motors. At rated load, they draw 30A each. The motor controller supports two motors at 60A each (up to 100A intermittently). The SLA batteries would support this configuration also, rated for 255A max current draw. Unless I am missing something, all these components would seem to play nicely together, at least on paper.

I looked at golf cart motors briefly and those are some big boys (8-11HP!) compared to my setup and would draw much more current.

The hydrostatic drive suggestion is intriguing, but I was trying to avoid using "junkyard" parts, just to see what was possible with off the shelf parts anyone could purchase and replicate the build with.

 

[bj2386]

There's a simple way to bake a chain driven differential that can be adapted for pretty much any axle.

Split the axle precisely where you want the drive to be.
Add a pair of pillow blocks for the cut ends.

Add on couple retainer collars to eliminate axle slide out.

Then you need 2 freewheel thread adapters (kinda like for an adult trike) 2 freewheel sprags, and whatever sprocket size you intend to use.

You may or may not need spacers, but you use bolts to make a sandwich of the gears making sure to keep the freewheels properly oriented as RHD.

What this accomplishes is both wheels get driving power regardless of how much slip is encountered, but the wheel on the outside of a turn can freewheel to overtake the inside wheel without ever having consequential power loss.

Sorry. I may have created confusion by using an incorrect term in my original post. I was planning on using "differential steering" rather than "differential drive" (https://mae.ufl.edu/designlab/class projects/background information/steering.htm)

My plan is for the cart to have 4WD, which differential steering schemes have by default. There won't be any live axles in this arrangement.