Mountain Wheelchair Motors have been left at Halfords

This was the scariest moment so far in the mountain wheelchair build…

Last night, I dropped off all of the motors and wheel rims at Halfords Autocentre in LLandudno.

This will be first task that I’ve had to get somebody else in to complete and I felt extremely nervous walking away, leaving all of the wheelchair parts in somebody else’s hands – What if they don’t do a good job of it? What if they drop one of the motors? What if something gets damaged? Do they realise how important they are?

To be honest, the two people I spoke to were very reassuring, and the girl at the counter added to the label “Guard with your life”.

They were kind enough to let me take a photo for the blog – “bye bye motors, it was nice knowing you”

And, they even said they’d take some photos as they carried out the work which was pretty cool.

If you’re reading this Will, then I’d just like to say a big thank you for offering to do it. In the end I thought it best to go to a store to do it because it meant that if they did get damaged then I’d be able to recover the costs.

All in all, I’m a little nervous, but at the same time extremely excited. The wheels were one of the first things I started thinking about when I began this journey. Once the motors are sitting in their rims, they will be the first part the mountain wheelchair which will be finished. No more research, no more designing, done, finito!

So long as everything goes well of course :S

*Update*

Received a call from Halfords the following day to say that they had done all of the measurements and found that they needed an odd size spoke which they couldn’t obtain from their suppliers. They did however email me a link to some on ebay, but they’d need to be shipped from China. The good news is that they’ve done all of the measurements and at least now I know what size spokes to get.

I’ve been into Halfords to collect the motors as the motor controllers will soon be arriving and I want to start playing with the electronics whilst I’m waiting for spokes to arrive.

Controlling the Beast

I’ve spent a lot of time watching the current prototype climbing over large obstacles and it appears that when it’s in an awkward position it might be very useful to have complete control over which wheels have power going to them. If the motors are embedded in the wheel hubs then this would be easy to achieve. The only thing that needs to be given much consideration here is the user controls. The image below shows an initial concept of what these controls might look like:

Whilst this is just a concept, research could be done into ergonomics and inspiration taken from gaming controllers:

As mentioned though, delivering drive to individual wheels is easy if each wheel has an embedded motor. If one motor is used for each side of the vehicle, so one motor for three wheels, it becomes far more complicated. I’m not sure how this would work but I imagine it would have something to do with engaging and disengaging gears.

Motor/Wheel Choice and Wheelchair Measurements

Over the weekend Ada and I went into Colwyn Bay KTM and Honda to look at quad bike wheels and see what inspiration could be drawn. Originally I had in my mind that the wheelchair was going to use fat, chunky quad bike wheels to provide better grip on the wet rocks, however, for some time I’ve been thinking that a thinner 12″ wheel would probably do the job. Low-and-behold as we walked into KTM I was instantly drawn to this 12″ wheel on the back of a pit bike.

It somehow seems smaller in the photos but I think it’s ideal. Without measuring the steps at the top of Snowdon and doing a lot more testing I won’t know for certain if 12″ is the right size but they do help to keep the overall weight down, will mean the wheelchair is more likely to fit through narrow gates and stair cases, and will look less menacing to mountain walkers.

12″ wheels with 3000w motors built into the hubs are also readily available:

However, I am more drawn to the 13″ wheel which is capable of producing 225Nm torque, whereas the 12″ only 182Nm. Another useful feature of the 13″ wheel is that the wheel rim easily detaches from the hub. At £400 each (and I think we’ll need six), the motors are probably going to be the most expensive part of this build. If a rim gets damaged, it means that you can just replace the rim without having to replace the whole motor. It also means you can easily change the tyres so that you could have a set of both off-road and road going tyres.

These 13″ wheels take a 130/60-13 tyre such as this Maxxis M6024:

Combined, the wheel and tyre would have an outside diameter of 19″ and a width of 5″.

This means that if the wheels were touching each other, the shortest possible length of a 6 wheeled vehicle is nearly 60″. This size needs to be increased though to allow the rocker bogie mechanism to work. I don’t yet know if a 19″ wheel will be suitable to get up the steps at the top of Snowdon but thinking about the overall size of the wheelchair, I certainly don’t want to go any bigger than this if possible. Generally speaking though, a rocker bogie mechanism is capable of overcoming obstacles which are twice the wheel height. For a 19″ wheel that’s 38″, or three and a half feet. Imagine seeing a wheelchair drive over a 3 1/2 foot tall obstacle!!!

Taking the measurements of these wheels and combining them with the measurements of Ada’s current wheelchair, the following is a scale drawing of what the finished wheelchair might look like.

Although this is a very rough concept and room needs to be made for the differential and batteries, and at the moment the positioning of Ada’s feet will dictate the maximum size of obstacle it can overcome, it does at least give some sense of scale and is a better representation than the current working prototype.

Not only is it alive, but it works, ish…

I woke up in the early hours of the morning and popped down stairs to see how the printers were doing. To my excitement all of the parts were finished so I sat at 2:00am constructing the prototype. Several hours later I went back to bed excited to wake up and show the family what I’d created:

It works! The prototype works! Well sort of…

The cheap motors I’m using seem to be slipping a lot which means that often the motors are turning but the wheels aren’t. There also doesn’t seem to be much grip in the tyres so often they just wheelspin instead of climbing over obstacles. I knew this was going to be an issue when I bought the motors but as a first working prototype it does at least show that the concept works.