_^30/07/2023

I want to build an electric motor and it better be DIY!

In this episode of How Can I Make My Life Harder and My Wallet Thinner, I want to build a fully functional electric motor from scratch. This is the first entry of a (hopefully :^)) long series of posts where I’ll document my progress.

Big picture; I want to go on biking trips with my girlfriend. Also I’d like to make my grocery trips by a bike but since it’s hilly where I live, I need some help.

Small picture; I’d like to know how the motors work. Since magnets are magic, motors are magic too.

Since this is a big project, I’ll break it down into smaller pieces and post them here as I go. First order of business is to get specifications for the bike. The motor and the battery will be designed around the bike. I’m not going to mess around with the battery since Li-ion batteries scare me and that’s not a phobia folks, it’s a healthy respect for a dangerous thing.

At the bare minimum it should be …

• foldable so that I can take it with me on the train.
• able to carry my weight and all of the equipment I’ll need for a trip.
• able to go 20 km on a single charge.
• able to go 25 km/h on flat ground.
• be cheaper than a ready-made electric bike.

It would be great if it …

• could carry me and my girlfriend.
• had pedal assist instead of a throttle.
• had regenerative braking for some super capacitors and assists me during take-off.

I’m a bit chunky, so I’ll need a motor that can provide a lot of torque. I’m also a bit lengthy, so I’d need to buy a higher saddle, me think so. I don’t need a lot of speed, I’d much prefer higher efficiency and longer range. It’s not going to be a hub motor since I don’t want to mess with the wheel. Also, a bit worried about the carrying capacity of the bike. Since foldable bikes are not known for their strength, I’ll have to make additions to the frame.

The cost is also a big factor, I don’t want to spend more than 500$ on the whole thing because I could buy a ready-made bike for that price. I was thinking around 90$ for the bike, 90$ for the motor and around 50$ - 100$ for the battery depending on the type and capacity of the battery. Prices may seem low but I’m planning to buy used parts and make the rest myself, also the local prices are a lot lower than the US prices.

My main plan of attack is as follows:

• Research how much torque I need to go up a hill, how much power I need to go 25 km/h on flat ground, how much energy I need to go 20 km.
• Research how much power I can get from a motor of a given size and decide on the motor size.
• Buy a used regular foldable bike.
• Design the motor and the battery around the bike.
• 3D print the parts and assemble the motor.
• Mount the motor on the bike.

Sounds simple but I’m sweating already. So in the next post, I’ll start with the first item on the list.