Electric Recumbent Motor

22 09 2012

The journey has begun for my electrically assisted recumbent bicycle. I’ve collected a lot of parts, including the donor bicycles, some steel for construction, some of the batteries and the all important motor. I’ve decided to use a BLDC motor from a Fisher & Paykel washing machine (must be a model with the Smart Drive motor). This is for a few reasons; they are cheap to get, powerful and have permanent magnets in the rotor. Cheapness is important to me as I am a low income earner, I got the entire washing machine for AUD$5.50 off Ebay. So, for an approximately 1kW motor, that is a pretty awesome deal I think. The permanent magnet side of things is also important because I am wanting to investigate regenerative braking on this build and I am led to believe that these are more efficient in that regard. Most people that use these motors as generators usually rewire them for better voltages, but I am going to go with the stock motor first and see how it goes.

Here are some pictures of the tear down of the washing machine and preparation of the motor for mounting. I got the washing machine for cheap because it had stopped working and after the previous owners spent some money replacing the water pump, they gave up on it when it still wouldn’t go. Most of the time the power drive transistors on the control board burn out on these models and a handful of components can get them working again. But, I’m not interested in riding a washing machine all day, I’m interested in bicycles and how to make them go fast.

Fisher and Paykel washing machine with Smart Drive motor. Bought off Ebay for cheap.

To remove the tub and motor assembly, the four support rods on either corner have to be removed first. The top right has already been taken off in this photo. I just grabbed hold of the motor shaft inside the tub and lifted slightly to be able to lift off the grey holders on each corner. It worked well for me.

This is a picture of the tub and motor assembly once removed. The motor is the grey part on the bottom. The problem with this design is that it is hard to remove the motor from the tub. So, I decided to just cut away the tub right back to the part that holds the bearings and shaft.

First I drilled a hole in the side of the tub big enough to fit my jigsaw blade through, then cut around the perimeter to remove the top.

At this point I removed the rotor and stator then started cutting either side of the support sections that run out from the central hub up to the next cross support. After that it was just a matter of snapping each part out along the cross support. With the wider sections near the outer rim of the tub, I had to cut them into smaller sections before trying to snap them because, if I didn’t, they would only bend and not snap.

Cut down to the last lot of support sections.

This is as far as I could cut down the tub with my jigsaw.

To remove the last bits of the supports I tried both a hacksaw and rotary tool with a cut off disk inserted. The rotary tool won out at the end of the day but I had to be careful when cutting because it melts the, what I assume to be, nylon and it can wrap itself around the shaft. As it builds up it ends up snapping the cutting disc. I got around this by cutting through in layers and removing the build up around the cut as I went.

I used the barrel sander attachment on my rotary tool to sand back the remaining stubs to leave a nice finish on the hub.

 

After the hub was finished I reassembled the motor. You can see on this photo that the stator has some cracks in it. Apparently this is a fairly common occurrence with these motors. I think I will end up impregnating the cracks with some epoxy using some kind of vacuum set up to prevent it splitting further.

 

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