DIY Electric Golf Trolley

I made this golf trolley about four years back as a winter project. I was beginning to find that carrying my golf bag for 18 holes was a bit tough on my back and knees.

I bought the motor/gearbox and 2 back wheels for about £90 from Standel Dawman, a company I found on the Internet.

The wheels have a built-in freewheel mechanism so the trolley coasts downhill and is easy to turn, too. The axle is 12-mm steel rod, drilled to take spring pins that hold the wheels. Later, I modified it to a tubular axle with solid stubs in each end to save weight (and just for the fun of it!). The gearbox provides the left side bearing. The right side has a ball race (steel balls in a plastic housing), wrapped in polythene to keep the dirt out.

Cardboard Aided Design (CAD)

The basic plan was sketched and pretty much done by guesswork, taking some dimensions from a friend's Powakaddy golf trolley. The folding mechanism was worked out by CAD (cardboard-aided design), and was the trickiest bit. The central arm folds, but broke a couple of times. So, I gradually increased the dimensions. I welded-up rods on plates for the main pivots, where the A-frame at the back joins onto the chassis tray and the sliding loop, which locks the two parts of the central spine when in use.

It is all made of plywood bent with the aid of a hot-air gun. Where the radius was too tight, it was laminated out of thinner sheets of ply. The pieces were cut, bent and then glued together with a bit of bracing added in an ad-hoc manner to hold the battery and support the bag. I had to modify it slightly when I bought a new golf bag, but that's easy when you've built it yourself.

Speed Controller Specs

The speed controller should have been easy since I'm an electronics designer; however, I learned a few new things. The basic control is pulse width modulated. The actual variation of pulse width between a gentle crawl (when loaded) and full speed is a relatively small. The controller is based on a hex inverter CMOS chip with a few Rs, Cs, and a pot. This drives a pair of decent power FETs in parallel. I have an 0.15R resistor in series with each one just to "calm things down a tad" as the stall current at switch-on can be rather high, and I wanted to ensure reliability.

The first version flattened batteries rather quickly. I then added a "flywheel diode" (4qdtech.com had some excellent stuff which taught/reminded me of stuff I should have known) that greatly enhanced the battery life.

The other electronic problem was the charger for the 20 Ah gel battery. Many trolleys use bigger batteries, but they are heavy (which is self defeating). My old car battery charger ruined the first gel cell, so I built a two-stage charger, 3 amps up to a certain voltage and then a constant voltage trickle. Voltages and currents were obtained from the battery manufacturer's website, which is the only really reliable source of information.

Reliability and Rubbish

The trolley works very well and has proved more reliable than some of the cheap ones which appeared on the market a couple of years ago. Oh yes ... the front wheel? It came from a child's ride on toy I found at the council rubbish tip!

Now it's time to go golfing!