All of the Wheels are Laced… and a Big “?”

Yesterday, when I got home from work, I was absolutely shattered and didn’t want to do much of anything other than lay down on the sofa and fall asleep, but as I lay there, struggling to keep my eyes open, I glanced over at the mountain wheelchair parts and decided to crack on!

I’m really glad I did as I managed to get all six wheels laced. Ta-da! Six wheels for the mountain wheelchair!

It’s taken quite a lot of modification for the wheel rims to accommodate the spokes. I think they might be motorbike or scooter spokes? By the time I’d finished the fifth and six wheels, I realised I’d done a much better job of these than I had the first and second wheel. With this in mind, I will definitely need to do two wheels again and perhaps even four. Still, I’m really happy with the result and the spokes look like they’re up to the task of transferring the motor torque to the wheels.

As I was tidying up the mess I’d made in my “living room” whilst lacing the wheels, I decided to throw out the boxes that the motors had arrived in. The sense of elation I got just from throwing out some boxes is, in a sense, quite funny. For me though it signified a step forward. No longer are the motors being kept in storage; I’ve actually started building this thing!

The really cool, yet at the same time worrying thing about having all of the wheels made is that in the process, I realised how quick and easy it would be to make a four-wheel-drive platform for testing purposes. Nothing complicated as I don’t want to waste too much time on it, just a plank of wood laid across four wheels would be sufficient. This would at least allow me to see if four of these motors are capable of carrying a heavy bloke like me up a hill. If not, then it will put a huge question mark over the entire Mountain Wheelchair project!

First look at the Mountain Wheelchair Motors

So the 6 motors which will be used on the mountain wheelchair arrived this morning and I couldn’t help but open them up to take a look inside to make sure they were up to spec’.

Externally, the build quality looks great are the dimensions are perfect for the wheelchair. To get inside the motors you need a special tool usually, so I was really pleased when I undid the screws on the housing and it easily lifted away.

With the housing off, the first thing I noticed was that if I turn the axle, the motor spins much faster. 5 times faster to be precise. So that’s the first thing ticked; the motors will be able to spin at their optimal speed thus improving their efficiency, reducing the heat they generate, and all the while producing more torque.

Motor Windings

The second thing I noticed was that there are in fact 32 magnets with 16 pair poles, unlike many of the cheaper motors which have fewer magnets. This should result in a quieter motor with improved torque.

The motor also has a 20T winding (all of the copper wires which are wrapped around the “magnets”):

These copper coils are what create an electromagnetic field when electricity is passed through them. As the “magnets” turn on and off in the right sequence, it turns the motor. Typically, the hub motors on ebikes have 6 to 10 windings (the amount of times the copper is wrapped around to create a magnet). A bike with 6 windings will travel at a higher speed; because there is less copper for the electricity to pass through it gets where it needs to be quicker. A 10 turn winding motor will therefore go slower because it takes more time for the electricity to pass through the coils. What this Chinese company have done for me is 20 turns which means that although the electricity will take twice as long (in simple terms) to pass through the coils, the resultant electromagnetic force will be twice as strong, thus resulting in a motor which has far more torque and travels at a speed which is more appropriate to a mountain going wheelchair.

Planetary Gears

Although I was happy with what I’d seen so far, I must admit I was a little disappointed with what I found when I extracted the motor from the housing; plastic Gears!

Presumably the gears are made from ABS or Nylon and should last some time, but I can see myself having to service them in the future. At least I’ve got a 3D printer though so might be able to make the gears myself. I would have preferred steel(?) gears but I imagine these plastic ones will at least be quieter and cheaper to replace.

Freewheel Mechanism

Finally the other thing I wanted to have a look at was the freewheel mechanism. Bicycles are intended to roll down hill without the rider having to pedal constantly. For this to happen geared e-bike hub motors have an internal freewheel mechanism. For the mountain wheelchair, this presents a problem because when put into reverse, the motors would just spin freely without turning the wheels.

I’ve read about some people overcoming this problem by welding the freewheel mechanism, but the company that made these motors for me came up with a far more elegant solution. I believe it’s called a Woodruff Key?

Verdict

So all in all, I’m a little sceptical about the plastic gears, but other than that I’m really happy with these motors; they’re lighter than direct drive hub motors, consume less power, they have internal temperature sensors but are less likely to overheat anyway, they’re well engineered, and importantly they should provide more than enough torque to get this wheelchair into the mountains.

In Other News

Now that I have both the hub motors and the wheel rims, I need to get the two things attached to each other. I’m not sure what, but something in the back of my mind tells me that it’s quite difficult to balance a rim on a hub. Add to that the fact that I don’t know what size spokes I need, I figured it was time to get some external help.

The first thing I did was ring West End Cycles in Colwyn Bay. The quote they provided over the phone, for all six wheels, was nearly £1,000! Just for putting some spokes on! Perhaps I’m just not appreciating how difficult it is?

I then rang Halfords in Colwyn Bay. They wanted £25 in labour per wheel, and although the guy on the phone was struggling to find the best price for spokes, he was able to find some which would cost about £35 per wheel. This puts the total quote from Halfords at £360.

Finally, I’ve got one more person to try who I discovered lives just around the corner from me. When I’m not so full of cold I’ll ask for him to have a look and take it from there.

This page was last updated on April 18th, 2018 by .
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