Homemade electric scooter ( for free ?! )

    Recently my friend rolled up to my house with his new electric scooter and today I finally snapped and decided to make my own. These scooters happen to be quite expensive, the one my friend had cost him 500€ - that's more than my car! I'm trying really hard to save up for another car I'm restoring so anything more than "for free" is too expensive for me. Fortunately I happen to have a bunch of junk laying around ready to be repurposed. So let's get into the build!

   First I had to find what I think is the most important part, which is the electric motor. When you see a DIY electric scooter it either has an off the shelf motor made for scooters, or a large BLDC motor, these can be expensive and hard to find. Some smaller scooters use cordless drill motors, which are rather weak, and some even use alternators converted to BLDC motors, which require drivers and the alternators themselves are really big. Another option is to use hoverboard motors for scooter conversions but these can also be hard to find. 

    My solution to this? Car radiator fan motors. Now let me explain how did I come up with this idea. It all started with me crashing my car last year in a head on collision. While pulling the front end apart I noticed that the fan was deformed so I decided to pull it apart and throw the plastic fan and fan shroud in the recycling bin but I kept the motor. I noticed at that moment that the motor was quite large and I immediately realized it had potential. And when you think about it nobody is using these motors anyways and since they're in the fan they're not even that hard to find and much cheaper than an alternator. It's quite big but not huge, about the size of those cheap e-bike kit motors that you can find sometimes. The particular motor I used came from a SAAB.

    Now that I had the motor I had to find a way to make it spin the rear wheel. At first I noticed the slightly rusty flange on the shaft and thought that I could just weld a tube or a chain sprocket to it to make it spin the rear wheel. I couldn't find a sprocket that would fit right so I chose to make it a friction drive. For this I cut out a piece of scrap ~48mm steel pipe but no matter how hard I tried I couldn't weld it to the flange. I suspect the flange is made of sintered steel and as soon as I tried to weld to it the weld didn't stick at all.

    So I decided to take the flange off and to try attach something to the shaft directly. At first I didn't know how the flange was connected, it could have been threaded on. My way of removing the flange was to drill a couple of holes as close as possible to the shaft and since the material seemed brittle my hope was to crack the piece in half. 

    After I jammed my flat head screwdriver into the gap I noticed a small crack in the flange near the shaft so I pried some more and the flange came off. The shaft on this motor is 8mm thick but only about 10-12mm long so mounting was a little harder than usual. My choice was to take a long M8 nut and to drill half way through with an 8mm drill. I then cut a slit in the side of the nut to allow it to be clamped and tightened on the shaft. This way I could attach whatever I wanted to the motor with an M8 bolt.

    Next I had to attach the pipe I had earlier to this shaft and I did that with a piece of 20x4mm flat bar. First I drilled an 8mm hole in the flat bar and then I cut it into shape to fit into the pipe tightly. I then welded the flat bar in place with a couple of tacks.

    Up to this point this was the only part where I used my welder. If you don't have a welder you can make wooden discs to fill the steel pipe or use a skateboard wheel. And now that this part was done I could bolt it on to the shaft of the motor and start mounting the motor to my scooter.

    I thought that the rusty pipe would be rough enough to get enough grip to spin the rear wheel but that was not the case. The super old tire didn't help with grip either so I decided to weld a couple of tacks around the pipe to help it grip. After I added the tacks I also ground away the sharp points with the angle grinder to make sure they don't eat away my tires. If you don't have a welder you can roughen up the surface with an angle grinder or a metal file.

    This helped out alot with grip, but the old rear tire was not helping much. Fortunately the front tire had been replaced so I just had to swap the wheels around and I was good to go.

    Now let's talk about the scooter I used for this conversion. It is my old scooter that I had since I was about 5 years old but I never used it because it had a flat tire and my dad couldn't be bothered to fix it. When I pulled it out of the shed I was actually surprised at how tiny it was because I remember it being much bigger. This scooter has rather large wheels, I think they're 12 inch wheels and that's great because they should make the ride smoother.

    To mount the motor I used the existing holes in the frame and some 25x25 angle iron to make the brackets. For power I used a lead acid battery that I pulled out from my new car because I had a bigger better battery to take it's place and this one sat unused. Also it's a 32Ah battery, which is too small for my car but great for this scooter. To control the motor I used a relay that I pulled out from my old car that I crashed and routed two wires to the handle bars. When I connect these together the motor spins.

    After the first test drive I noticed that my shaft coupling was not staying on and the friction drive part would fall off. I tried tightening it more but there was too much load and it didn't stay on for very long so I just welded the nut onto the shaft. Of course I'm a man of many ideas and there are other ways this could have been done. For example if you also rounded the outside part of the nut that goes on the shaft you could thread the outside of the nut with a M12 thread and if you threaded it with the gap closed, so that the thread came out tapered, tightening an M12 nut would also tighten the coupling on the shaft. Not sure if I explained this well enough but basically there are other ways to clamp on to the shaft and I just chose the easy way out. Also I positioned the motor in a way that driving the wheel makes it tighten the bolt that holds the friction component on, kind of like the nut on an angle grinder.

    And finally now that all the trials and tribulations were out of the way and over with I could take the scooter out on the street and test drive it. And guess what, it drives great, and the speed is also pretty good. But it didn't take long for the old white tire to blow out. Fortunately I was able to find an old 12 inch wheel from my younger brothers' old bike and continue driving.

    Later I decided to check the max speed of the scooter and was pleasantly surprised to see a stable 15km/h, which is not bad at all. The motor I used has plenty of torque I'm pretty sure I could make the scooter go even faster but the friction drive seems to be the bottleneck in this case as it tends to slip and creates alot of unnecessary heat. The battery mounting sitation was not ideal, I had it taped to the frame but it fell out and smashed the relay I was using to control the motor. The solution to this was of course to use more tape.

    After some driving around I checked the motor and it was just barely warm but what concerned me was that my wires were getting hot. To remedy this I replaced the thin wires with thicker ones and shortened the overall length of the wires to decrease resistance even further.

    This turned out to be a very fun one day project and I think that I'll also add a seat next to make it more comfortable to drive and perhaps a chain drive in the future. I'll be sure to keep you posted on the future development of this e-scooter.

That's it for now, thanks for visiting my blog.