Alex’s Electric Bike

Alex's Electric Bike

Alex Holberg

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I started considering converting my bike into an electric, when I got a job in a location quite a bit further from my home than I was used to. I was still committed to doing the daily commute by bike, but as it turns out, having to sink two hours into commuting each day, along with the fatigue coming from starting at a new workplace, was enough motivation to start this project.

The bike I had been using up until now was still perfectly functional, and quite nice, so I started looking into upgrading a bike to an electric. There are several different kits online for doing that, and most are going to be a better solution than what I would be able to make. Nevertheless, I decided that If I was going to do this myself, I might as well go all the way and see if I could save a little money at the expense of my time.

Doing something yourself grants you understanding, and removes the hesitation to perform upgrades or otherwise tinker with a build. I would be scared of breaking something I didn’t understand to a large extent, since I may not be able to put it back together.

Materials

  • A bike
  • Motor
  • Speed controller + Throttle
  • Battery
  • Electrical wires
  • Mounting hardware (Nuts and bolts, brackets)

For the project, I used a Brushed 500W motor and accompanying speed controller and throttle. These were all packed together, and cost about 1000dkk. 

500w is overkill for a bicycle, you can get a 250w kit for less and save quite a bit of cash. I might be using this kit for other projects in the future, so I went big.

Next we need a battery. It is possible to use lead-acid batteries, and they are much cheaper, but also considerably heavier. If you want to use a lead-acid battery, make sure it is a deep cycle battery (sometimes called a truck battery), as it would otherwise only last you a couple charge-discharge cycles.

I ended up paying extra, and got a nice lithium bicycle battery capable of providing 500w for about 3000 dkk. It has a perfect form-factor for a bike, and is easy to remove and recharge with the included charger.

For the drive mechanism, I used a little wheel, 3D printed in ABS plastic attached to the motor. This wheel would contact the tyre on the bike and drive it that way. I recommend using something with more of a direct transfer of power. (more on that below)

The rest are all smaller items which you can get from a hardware store, (or scrounge from your uncles workshop)

Odd nuts and bolts (Remember to get locking nuts, as there will be vibration)

Mounting brackets (we ended up bolting together two spare pieces of aluminium)

The Build Process

Initially, all electronics were connected on a flat surface, to ensure everything was functional. 

The connector from the battery needed modification, since it contained a brushless speed controller, which was incompatible with the current system. The speed controller was removed by removing the battery and opening the battery connector. Inside, there was a circuit board covered in silicone for ingress and vibration protection. Scraping off the silicone reveals a few screws for dismounting the PCB. The power supply wires were cut as close to the PCB as possible, and the PCB removed. The supply wires were then extended with some spare electrical cable and connected to the power input of the brushed speed controller for the bike.

Next, the throttle, motor and kill switch were connected to the speed controller. This was done by following the instructions included with the speed controller. In general, the throttle will be three wires, the motor and power will be thicker wires and the power will follow the traditional red-black coloring.

After the throttle could make the motor spin, the mounting could ensue.

The electronics were mounted by drilling holes in the bike frame, and threading them. This was enough to fasten the electronics, but did leave it a bit wobbly. This could be solved in the future by drilling through the frame and using screw nuts or adding a bracket.

The throttle is mounted by removing the grip from the handlebars (compressed air works wonders for this) and simply screwing the clamping mechanism down, until it fits tightly and doesn’t move.

The motor mount was a bit more complicated. Some spare pieces of aluminium were used to center the motor over the tyre. Two pieces were angled in such a way that the position of the motor could be changed a little by loosening and refastening the nuts. I would strongly encourage you to find a better way of driving the bike than using a wheel, but it will work.

To protect the electronics from water and dirt, we used some plastic bags and duct tape as a “temporary” solution, until I can be bothered to install it in a box.

After this, the bike was ready for a spin.

Maintenance

Apart from having to maintain the bike itself, there are a few points to be aware of.

Because of all the dirt ever, the air intakes on the motor got filled with dirt and needed to be cleaned semi-regularly. At some point one of the filters got loose, and I had to clean the inside of the motor.

Learnings

I would not recommend using the same method of driving the bike, as there is not enough friction in wet weather, and the wear on the drive-wheel and tyre is considerable. Also, the hole in the mud guard would cause crud from the road to spray in all possible directions.

Going forward, I would upgrade to using a chain and sprocket method for driving the bike and closing the hole in the mudguard. Additionally, I would like to install the electronics and wires in a more aesthetically pleasing manner, getting a box for the speed controller and wire junctions, and perhaps getting some sleeving for the wires connecting to the throttle and motor. I might even figure out how to make the motor and electronics detachable, so I can put it on different platforms. Maybe a go-cart or drift trike. For now though, I’ll be moving on to some less mechanical projects for a little while.

A bit about Alex

I’m a Software Engineer, with way too many interests and way too little time to execute them.

If it looks or smells like Science, Radio, Electronics, or Software, you can probably get me excited about it.

This is why my catchphrase around the space has been “I’m into it!”.