Something many people don't know about me, especially online, is that I was injured a few years ago in a motocross crash where I broke my C3, C4, and C5 vertebrae in my neck. The resulting damage to my spinal cord left me partially paralyzed.
After far too long trying to use commercially available and outrageously overpriced power wheelchairs, I gave up on a big name manufacturer building something adequate. The technology is here. It has been for 10+ years. It has not been implemented simply because the manufacturers do not have to. Why develop something proper when you can reuse the same 30+ year old technology and still charge a premium - and by premium I mean $25,000 or more? There is no other alternative unless you do it yourself. Which is what I did. Follow along as I build something better. Skip ahead to page 6 by scrolling to the bottom of this page for videos (including some unmanned R/C driving. Yes, it has R/C capability) if you don't care to see in progress machining pictures. And feel free to leave a comment at the bottom of this page. Positive or negative.
Above: Let's start off with some specs of the final product that this is about before moving forward:
Length: 34.5" from the back of the rear tires to the front of the casters
Width: 25.5" from outside to outside of the rear tires
Height: 17" from the floor to seat pan
Ground Clearance: Not the paltry 2 to 4 inches of most powerchairs or scooters, but 6.5"
Speed: 13.5 mph. No, that is not a typo. 13.5 mph. Typical high end powerchairs are 6 mph tops. Too slow to be safe. Yes, faster is safer. Think crossing the street or trying to get out from behind the lifted Ford F250 being driven by the teenage girl on her cellphone in the parking lot of Tractor Supply. The faster you can get into a safe area the better. What if it starts to rain and you are a mile from your car or house? You get under a roof quicker. What if it is 20 degrees F? You won't be in the cold as long. What if a leprechaun is after ye Lucky Charms? You have a better chance of keeping your breakfast.
Range: 20+ miles of REAL WORLD USE. However, range is so influenced by contributing factors such as user weight, terrain, tire pressure, driving style, etc, etc, etc that a range figure is impossible to quote. Manufacturers give a range rating based on the "tennis court" distance. It's bs. Yes, a chair may go 20 miles on a flat smooth surface with Tinkerbelle in the seat before the controller shuts off. In real world use that same chair will probably go less than two miles with a normal 170 lb adult in it outdoors in the woods.
At the time of me writing this, my WillChair© (if you haven't figured out my name is William yet you are incredibly dense) is the only lithium powered brushless indoor/outdoor powerchair on the planet. Yes, there are lithium powered granny scooters as well as Invacare's gearless and brushless system, but there is no comparison. I have owned an Invacare G/B chair. This makes them look silly. This is, in my not so humble opinion and as far as I know of, the most capable and high performance powerchair ever built that is as equally at home indoors as out. See videos on page 6 for yourself.
All modern (and 40 year old) powerchairs use two 12 volt deep cycle lead acid batteries wired in series to create a 24v system. Lead batteries were all that were (safely) available in the 1970's. Great! However, the 1990's saw a huge leap forward in rechargeable battery technology. Lithium. They've been available and used extensively in everything from cellphones to watches to laptops to remote control cars to AA batteries for an even broader range of applications for 20 years now. Why not powerchairs? Good question. Why not?
There are several different types of lithium batteries, each of which has a different purpose. Lithium ion, like in your laptop or cellphone, is not suitable. They can't be recharged but 300 - 500 times (as good or better than the lead acid that is currently being used) and have a nasty habit of exploding or catching fire if mistreated. Not what I want under my tushie. Plus they don't like to have a lot of amps drawn from them at one time. Lithium Polymer, like in a remote control airplane, are not suitable either. They can't be recharged but a few dozen times. Oh yeah, and like most women, they can EXPLODE if made unhappy. There are several other lithium based battery chemistries that I am less familiar with that may or may not be good for powerchairs.
Lithium Iron Phosphate, or LiFePo4 for short, fit the bill nicely. They can be discharged at high amperages, have a cycle life of 2,000+ recharges if treated properly, (and many more than that is possible), do not explode or catch fire, and come in many different shapes and sizes for building into whatever size and voltage you need. For instance, something like this:
This is my 48v LiFePo4 pack built from 42 individual 15 amp hour 3.6v cells. They are wired 14 in series to give a total, fully charged voltage of 50.4 volts. The cells do not stay at 3.6 volts each very long. The actual working voltage for most of the pack is 46.5v. They are wired 3 in parallel. 14s (series) and 3p (parallel) for 45ah of capacity. Kudos to my better half, Sommer, for her help with the tedious assembly.
Most powerchair batteries are 60 to 70ah in capacity. However, due to Peukert's Law (Google search is your friend), powerchairs can only use roughly 50 to 60% of a lead battery's capacity, which means your 60ah of lead battery is only 30 to 40ah of usable power. LiFePo4 is not affected by such, and therefore, 45ah of a 45ah pack is usable.
Those little wires are for balancing each of the 14 individual parallel connections. Not difficult to figure out, but beyond the scope of this build page. Click to enlarge.
Running at 48v also changes the way power is removed from the battery. Voltage is basically the pressure. Amps is the current. Watts is the total amount of power, which is amps x volts = watts. Typical powerchairs run 24v. In order to get the same amount of power (torque to turn the motors), twice the amps must be applied. This magnifies that Peukert Effect (why have you not hit up Wikipedia yet?) on lead batteries. Even though lithiums are not really effected by Peukert's law, it's still easier on the batteries to run higher voltages and less amps. I would run 60v if I had my choice. Due to spacing for the cells in series as well as affordable chargers being unavailable is why I chose 48.
Go read up on Wheel Chair Driver for massive amounts of information on batteries that is beyond my knowledge, as well as all sorts of things chair related.
Where to even start? There are many different powerchair frames and chassis available. I looked until I was crosseyed and finally decided there was nothing to be bought that had the features and quality I was after. I had experience machining and decided to start from scratch.
Basically, all I did was determined the dimensions I needed to fit within and started from a blank slate. I had never used a CAD program before. I was teaching myself about battery technology, so why not go ahead and learn some computer aided design while I'm at it?
After several months of frustration staring at a computer I had the basics drawn and could see a workable design unfolding.
Several pictures of a few of the components as they looked in CAD. This photo to the left is one of the side plates.
Those are just a few of the drawings. There were many. MANY. After months at the computer driving myself nuts with designing something that looked to be close to what I had in mind it was time to start whittling my ideas out of metal.
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