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The purpose of the Trailwind is to provide power-assist for manual wheelchairs on rough terrain. It is NOT intended as full motorized wheelchair propulsion.
The power assist works to counter the rolling resistance created by rough terrain and inclines. The rougher the terrain or steeper the hill, the higher the power setting needs to be to counter the increased drag. Therefore, the power setting (throttle) will be changed as the terrain varies.
Personally, I enjoy wheelchair self-propulsion on nature trails using my trike wheelchair equipped with knobby tires. But many nature trails invariably have hills and slopes to contend with. Ascending an incline on gravel/grass/dirt/rocky/rooty/soft trail is much more difficult to climb than a paved slope. Self-propulsion on the previously described surfaces is much more difficult than on a paved surface. The power assist is designed to neutralize the “much more difficult” and make it the same as a level paved surface. In other words, if you can self-propel 5-10 miles on a paved rail trail, you should also be able to self-propel 5-10 miles on a gravel trail with hills using the Trailwind.
The Trailwind uses a 300 watt HUB motor that is mounted to the wheelchair camber tube allowing for Trailwind connection axle mount to rotate around the camber tube. Thus, enabling low wheelies for declines and obstacles clearance. The drive wheel trails behind the rear axle with the drive strut at about 45%.
Unlike a Smartdrive, it uses a pneumatic tire with tread, not an expensive Omni wheel. The turning resistance created by the trailing wheel is relatively minimal given that wheelchairs on rough terrain don’t do a lot of spinning maneuverers. The 45% angle of the drive strut results in the drive wheel pushing “up” into the camber tube as it drives forward. This action creates additional traction for inclines and loose terrain (i.e. the drive wheel doesn’t slip very much).
In the event of mechanical failure, drained battery, or to save electrical power, a cord can be used to elevate the drive wheel off the ground to reduce rolling drag. The weight of the Trailwind with one 4.4 AH battery is 12 lbs.
Specifications:
• The Trailwind uses a 300 watt/36 volt 10” off-road hoverboard HUB motor/wheel/tire from Swagtron ($50). I think other off-road wheels will also work fine.
• The battery is a 4.4AH 36 volt lithium battery ($40) commonly used on hoverboards. I am using two in parallel to double the range to – ten miles maybe? IDK yet.
• The components are mounted to a 1” square aluminum tube (scrap).
• The wheelchair camber tube is connected to a 8” concave slice of a 1 ¼” PVC tube (scrap) via two Velcro straps (scrap) on either side.
• The PVC tube is bolted to a piece of (scrap) plywood which is bolted to the 1” square tube.
• The battery is secured to the piece of plywood with Velcro strips and straps (scrap).
• The Universal Scooter Controller is secured to the 1” square tube (gorilla tape/zip ties – you decide).
• The Stop Button and battery are connected with XT60’s and wire (scrap).
The Stop Button and Thumb Throttle go under the wheelchair, up between your legs and sit in your lap for easy access.
For those counting, the price of all the components is $145 which includes FREE shipping. If you have to buy Velcro and some straps it might cost you $20 more. Maybe $20 for the wiring and XT60 connectors. The total cost should be around $200.
If you have used hoverboard, scooter parts and some scrap materials, you may only need to buy the $10 Stop Button (A MUST HAVE!!!).
I am sure some people are thinking that the 10” wheel could be replaced with a smaller/lighter 6.5” 150 watt hoverboard wheel and be used on pavement as a regular wheelchair power-assist. They are likely correct. I haven’t done that yet. That is next on my list. A hoverboard HUB motor is connected on one side of the axle. I think a scooter drive wheel could also be used and connected on both sides using two struts. BTW, a Smartdrive can cost as much as $8,000 which is 40X the cost of the DIY Trailwind. Something seems fishy to me.
There are likely better ways to connect the Trailwind to the camber tube. Hopefully someone will come up with something and open source it. The method I am using is only my first idea. More will come to me later.
It is important to keep in mind that the DIY Trailwind is a power-assist. It is a force multiplier. It is NOT a skill multiplier. It can help you go up a very steep rough terrain trail. But if you don’t have the wheelchair skills to get back down, you can get yourself into trouble FAST. The DIY amplifies your propulsion power, but it doesn’t increase your ability to manage and balance a wheelchair on difficult terrain.
With the added propulsion power, you will also need some type of DIY trike wheel or Free Wheel/Front Wheel or have large front caster wheels. Otherwise, you are likely to flip over forward when your front caster wheel is stopped by an obstruction. My guess is that the Trailwind should work on a beach, but I have not tested it on sand as of this time. Packed snow too should also be doable.
Note: The original device was created by Max Fan (and I as his consultant), as part of his senior Thesis project at MIT. He deserves the credit for putting the device together, particularly figuring out all the electronics. I have since modified the wheelchair/device connection to its current state. It was always our goal to open source the device as I am doing now.
Exhibit A – Conceptual Connections
• The Thumb throttle is connected to the Universal Scooter Motor Controller (USMC)
• The Stop Button is connected to the battery which is connected to the USMC.
• The HUB motor is connected to the USMC.
• The HUB motor is connected to the drive strut via an axle clamp.
• The plywood platform is connected to the drive strut.
• The battery is connected to the plywood platform.
• The concave PVC adapter is connected to the plywood platform.
• The wheelchair camber tube is connected to the PVC adapter.
How exactly these connections are made is up to you. My general prototyping philosophy is to make things as simple and cheap as possible and see what breaks first. Then I reinforce/change whatever breaks.
The top of this hill in the first video is around 18 degrees. I am using the Trailwind set at full power. I am also self-propelling at full power.
For comparison, in the 2nd video below, I am NOT using the Trailwind on power assist mode. Notice that while I cannot go nearly as far or as fast up the incline, I still can go reasonably far up the hill WITHOUT the power assist turned on. This is due to the combination of a trike wheel, off-road tires, optimized wheelchair setup, and powerful self-propulsion technique/ability.