eMule - Golf Cart Conversion
Conversion of an electric golf cart to farm vehicle platform

Disclaimer

Note: At this time, this is just a proposal. It project has not been built, or even commenced (though the golf cart has been purchased). It is just an idea. Initially the intention is not a full robotic conversion, but to convert the golf cart to an agricultural platform, and maybe take it further later on.

Why?

why

Golf carts are not just for playing golf. They are actually miniature electric cars, and can be driven on roads in some parts of the world. They are increasingly being used for agricultural vehicles on flat properties as they are much safer than quad-bikes because the heavy batteries make for a very low center of gravity. (They are almost idiot proof). They also designed to not damage grass or turf, which every farmer will appreciate.

Second-hand electric golf carts are readily available to the enthusiast for a price, and with some effort they can be converted to agricultural carry vehicles. Don't expect as good a bargain as you might get from a motorised wheel chair unless you are going to do a lot of searching. Bargains tend to gravitate to dealers, who know how to get a better price for them, and aren't fooled into thinking they are useless because their batteries have been neglected.

An eMule can be used

  • to transport people (though they are probably best left in their original form if this is the primary use)
  • to transport equipment, tools, firewood, rubbish
  • as spray or spreader vehicles
  • as miniature tractors to pull things around, out, over or through. At a pinch they can pull a normal car trailer.


It is also fashionable to make vehicles which look like the M274 US army 'mules' popular after WWII and in Vietnam. The original M274s are now coveted collector's items.


This process would could be expected to involve five stages.

  • Buying the golf cart.
  • Stripping off the roof and panels, and installing a tray.
  • Making the accelerator, brake and steering usable with the new configuration.
  • Making the accelerator, brake and steering purely drive-by-wire.
  • Making the vehicle fully autonomous.

Buying the golf cart.

why

Golf carts are not like motor cars. They may only get used every week or two and spend most of their lives in a dry shed, and hence last a very long time. Buy an old golf car (mine was 25 years old) for this. Plenty of carts this old look like beaters (scratches, cracked panelling or windscreens, torn seat covers etc), but are still structurally quite sound. They will be a lot cheaper than a flash new-looking model coveted by some economically-stimulated golfer. And don't be shy about explaining to the helpful sales-lady: 'I am looking for something a bit unusual'. Trust me: she has had this request before.

Stripping off the roof and panels, and installing a tray.

why

Strip-down is actually straightforward. The panels, roof and windshield can be simply unbolted from the cart's chassis. The 'Club Car's have an aluminium frame, which make welding mild steel quite difficult, but this can be solved in other ways - like just bolting on the new frame. This is a good idea anyway, as a non-destructive conversion enables the original cart to be reassembled if there is a change of heart.

The tray can be welded with mild steel, in a simplified version of the M274.

Because the tray has to sit above the chassis, and therefore above the suspension points, it ends up being quite high - and the seat may be higher than it was in the original golf cart.

Making the accelerator, brake and steering usable with the new configuration.

why

The accelerator is a just a potentiometer on a pedal, so that should be pretty straightforward - the original can be brought over and re-wired for the extra distance.

The brake should be pretty straightforward - it is just a mechanical lever pulling a wire, which goes to the back wheels (there is no braking on the front wheels!). The golf cart has some mechanical trickery which makes a 'handbrake' on the foot, which disengages when the driver presses either the foot brake or the accelerator - that could be tricky to move across, but is not essential.

The steering is much harder. The steering column comes with a proper linkage, so the angle can be changed, but it's not clear how much. Note that the steering in the M294 Mule is pretty clumsy too. The existing steering wheel can go almost three full turns (ie almost 540 degrees to each side), so a lever attached to a linear actuator will not cut it.

Making the accelerator, brake and steering drive-by-wire.

If the accelerator, brake and steering were drive-by-wire, then the driver could just use a joystick or similar to control the vehicle, or turn control over to fully autonomous when required. why

The accelerator just just be replaced by a digital potentiometer (Maybe like the Digilint 410-239, but I have not used this device).

The brake pedal can be replaced by a linear actuator, which can pull the cable tight when required. Some force feedback would be desirable here. Maybe a force-sensitive resistor? I have not used those.

Steering is tricky. A powerful motor could turn the steering shaft, but position feedback is critical. Alternatively, the steering could be turned by having a linear actuator push/pull a bar on the steering column to turn it around, but this will limit the turn to less than 180 degrees, which is likely to severely reduce agility - already limited by the Ackerman steering. A linear actuator can be connected directly to the steering arm.

Making the vehicle purely autonomous.

why

This is just a matter of getting the onboard PC to control the accelerator, brake and steering. A new Helm.java variant may be required for this configuration.

Drive model

The code written to date has all been for a differential drive, so this will be a good test of the generic nature of the robot code. There is a generic 'Helm' object which can be specified to be either a 'DifferentialDriveHelm' or an 'AckermanHelm'.

This cart is likely to be faster than most differential drive robots. Electric wheelchairs are not designed for speed - too easy to dump Granny on the pavement. Although a golf cart has a modest top speed, its size, and Ackerman steering model create a whole new set of navigation real-time decision challenges.

Issues

Yeah, we all got issues.

Software

It would be pretty much the same as the other robots, except with an AckermanHelm instead of a DifferentialDriveHelm. No zero turn ability here, so the navigation would be different, and probably more cautious.

Bear in mind that even a zero turn rover can get stuck.

The future

Conversion to autonomous control.

Safety

Warning: This is a 500kg vehicle and moves at around 10km/h. It will kill someone in an accident, just like a motor car. Anyone thinking of building this kind of robot needs to think this through very carefully. It is also powerful enough to break through your boundary fence and start running around your neighbour's property, so this is also a serious liability issue. Think. Please.

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