How do electric wheelchairs turn/steer

Thread Starter

Jeffo123

Joined Jan 28, 2022
8
Hi,
I am looking into making electric wheelchairs cheaper, I understand the main components used for the drive system is a DC motor attach to a wheel, powered by a battery, and a joystick controller to move. I am just confused on the mechanism of steering the wheels with the joystick. What components are needed in order to change the angle of the steering by just moving the joystick? Is there another component attached to the wheels to turn it?
Any help is appreciated.
Thank you
 

panic mode

Joined Oct 10, 2011
2,301
how would a person sitting in a plain wheelchair steer if the chair has none of electrical devices on it?
they would use the hands to turn the wheels in the opposite direction... controlling both wheels at the same time is needed...
using two motors instead of two hands to power the wheels would have the same effect.
 

Jerry-Hat-Trick

Joined Aug 31, 2022
162
Conventional wheelchairs have two motors, as mentioned by "panic mode" one for each of the (big) wheels. Push the joystick forward and both wheels turn to go forward, push the joystick to the left and the right wheel goes forward, the left wheel backwards - you can literally turn on the spot - and so on. I happen to agree with you, they are expensive for what they are. Manufacturers are complacent, hiding behind safety standards. The actual electromechanical joystick needs to be robust and reliable but the overall electronics should not be expensive these days, and I do wonder if you could use windscreen wiper motors, made in millions so they are bound to be cheaper than motors "designed" for wheelchairs.
 

MrSalts

Joined Apr 2, 2020
2,354
Conventional wheelchairs have two motors, as mentioned by "panic mode" one for each of the (big) wheels. Push the joystick forward and both wheels turn to go forward, push the joystick to the left and the right wheel goes forward, the left wheel backwards - you can literally turn on the spot - and so on. I happen to agree with you, they are expensive for what they are. Manufacturers are complacent, hiding behind safety standards. The actual electromechanical joystick needs to be robust and reliable but the overall electronics should not be expensive these days, and I do wonder if you could use windscreen wiper motors, made in millions so they are bound to be cheaper than motors "designed" for wheelchairs.
Wiper motors are quite inefficient, get hot and not exactly what you want under Grandma's blanket as she roams around all kinds of terrain from shag carpet, sloped sidewalks, who-knows-what. Also, you'll need some method to detect when granny is coasting down the hill or when no signal is coming from granny's joystick because she just clipped the kitchen door and broke the arm off of the wheelchair and the joystick is on the ground. That is, you don't want the thing launching itself down the steps of granny's split-level ranch home because it doesn't know which way to go.

The last electric wheel chair I bought for a parent was easy to justify, it was about half the price of the bicycle by brother just bought. Wheel chairs aren't expensive, they are just made in low volume and carry some liability because a handicapped person is strapped to a lot of stored energy.
 

Irving

Joined Jan 30, 2016
3,133
The price of wheelchairs has little to do with works cost. In the US over 80% of chairs are sourced through insurance which artificially inflates the price. A fully spec'd chair like mine has a list price of £11k in the UK but I've seen prices of $33k for the same spec sourced through Medicare in the US. In the UK the NHS supplies (FOC to qualifying recipients) basic electric chairs with a retail tag of £6k, but they typically pay only around 50% of that. The retail price for direct purchase is inflated to allow for substantial margins to retailers of 15-20%, you cannot normally buy direct from manufacturer - I'm talking mainstream like Invacare, Ottobock and the like for chairs that people live in rather than just use for outside mobility. I'm also discounting the rash of cheap aluminium framed chairs with 8 or 10" drive wheels now available direct from China as these cannot, as a rule, be fitted with rehab seating for complex disability, also they're pretty rubbish to use on anything other than shopping mall smooth flooring.

There are pricing anomalies in the system: a replacement pair of 10km/h motors with gearboxes from Invacare (always replaced as pairs) costs upwards of £500. A similar but not identical motor from the German 'manufacturer' is around £140 or £280 a pair; similar but not a drop-in replacement as fixings, parameters and available gear-ratios are different. A similar motor, without gearbox as supplied to the German co, from the Chinese factory is as little as $40.

Windscreen motors won't cut it. Top-end chairs use 480W 24v motors generating 30Nm of stall torque pulling 100A+ when turning or starting on soft surfaces.

The R-Net CANBus control system, used on all top-end chairs, is also pricey; the joystick alone is £300! But you wouldn't want anything else for a high spec chair.

The UK has one indiginous manufacturer, Kilmore Chairs (yes, Tom has unfortunate surname), who builds a fully spec'd custom chair for around £7-8k. Expect a 6mo leadtime as each is a custom built one off and so avoids CE regs and Cat.2 Medical Device approvals.

Incidentally the second-hand value of chairs is low. An £11k full-spec chair (10km/h 4-pole motors, 120A controller, lighting, electrically adjustable 3-function seat & footrests) can be picked up s/hand for £2k 1 - 2y old or as little as £500 4-6y old.
 
Last edited:

panic mode

Joined Oct 10, 2011
2,301
assuming one wants to make a new product, proper approach is still to research. that includes how existing products work, and doing some number crunching (consider speed, range, payload, motor size, etc.) for intended use case (urban, off road or mix). this will push design choices in certain direction (drive type and size, control...). once that is determined, one can look at actual implementation details such as use interface (joystick or whatever)
 

MrSalts

Joined Apr 2, 2020
2,354
Also, there are some pretty cool manufacturing technologies that can be used to replace the stainless steel tube and panel construction of the old-school wheelchairs. Setting up sheet metal stamping and injection-molded parts with snap-in-place electronics could lower the price significantly vs the huge amount of labor (tube bending, pop-rivets, bolting/screwing) that goes into existing designs and manufacturing processes.
 

Irving

Joined Jan 30, 2016
3,133
assuming one wants to make a new product, proper approach is still to research. that includes how existing products work, and doing some number crunching (consider speed, range, payload, motor size, etc.) for intended use case (urban, off road or mix). this will push design choices in certain direction (drive type and size, control...). once that is determined, one can look at actual implementation details such as use interface (joystick or whatever)
As a moderator of a wheelchair user forum I regularly get emails from student groups who have been tasked with a project to 'design a better/cheaper/whatever wheelchair'. TBH there's not much you can do better than what's on offer today, though there are some rubbish ones and some good ones. The main improvements would be range, through lithium phosphate batteries + high-torque BLDC Hub motors, but not those rubbish 12v 'SLA replacement' batteries and better suspension.
 

MrSalts

Joined Apr 2, 2020
2,354
As a moderator of a wheelchair user forum I regularly get emails from student groups who have been tasked with a project to 'design a better/cheaper/whatever wheelchair'. TBH there's not much you can do better than what's on offer today, though there are some rubbish ones and some good ones. The main improvements would be range, through lithium phosphate batteries + high-torque BLDC Hub motors, but not those rubbish 12v 'SLA replacement' batteries and better suspension.
What do you mean by suspension?


Also, my criticism of wheel chair design was the seat is parallel to the ground. Just a 5° or 10° slope down to the back could prevent users from sliding out of the chairs. So many people sit in these chairs for most of their day - why not design with the geometry of a living room chair instead of the kitchen-chair geometry most seem to have. It's really sad that a design meant to roll someone from their hospital room to an x-ray was adopted as the design for people in nursing homes to sit in all day.
 

Irving

Joined Jan 30, 2016
3,133
stainless steel tube and panel construction
Rarely stainless, just powder-coated galvanised. And the tubing supporting the front castors is part of the suspension - you don't necessarily want a more rigid structure. Plus a good chair has to be tethered in a vehicle with pull-down straps and crash-certified with a 300kg body on-board. Whilst modern composites may have a part to play, a low CofG requires a certain mass.

Current chairs are fairly automated in construction and the bolt-on parts are there to facilitate replacement when they get bent.
 

Irving

Joined Jan 30, 2016
3,133
What do you mean by suspension?
Most low-end chairs rely on the seat-cushion to provide a degree of shock absorption from the rigid frame, while the front tubes and castor frames soften the jolt from hitting ridges and ruts. If you have specialist support seating you need to disconnect the seatframe or support from the motor/wheel combo. My chair puts the motor on a swing-arm with a rubber concertina section between the arm and the seat base support, highlighted yellow in the pic below. Some high-end chairs now use adjustable-rate monkey-bike springs instead.

1663361067240.png
 

Irving

Joined Jan 30, 2016
3,133
I have 'rise' on my chair and its invaluable; the downside is it adds 2" to the seat height, reducing leg room under tables.

There are a few stair-climbers, mostly experimental and none from mainstream suppliers. IMHO they severely compromise the chair's abilities, add weight, reduce ground clearance, etc.
 

Thread Starter

Jeffo123

Joined Jan 28, 2022
8
As a moderator of a wheelchair user forum I regularly get emails from student groups who have been tasked with a project to 'design a better/cheaper/whatever wheelchair'. TBH there's not much you can do better than what's on offer today, though there are some rubbish ones and some good ones. The main improvements would be range, through lithium phosphate batteries + high-torque BLDC Hub motors, but not those rubbish 12v 'SLA replacement' batteries and better suspension.
Yeah, I have started to realize this too. Have to compromise quite a bit of comfortability/cushioning and performance/functionality to make it more affordable. The main changes I was thinking of (component-wise) are changing the controller from an R-net to a VR2, switching to a lead acid battery, and probably switching the overall material to steel. The wheelchair I am trying to make is just going to be used indoors so I can make changes based on that that would make it cheaper based on requirements.
I also want it to be able to stand with a push of a button. Most of the high-end ones use an electric linear actuator. I've looked into other types of actuators like pneumatic and hydraulic but both these options aren't feasible or ends up costing more.
I guess I should focus more on trying to optimize the wheelchair frame design and its manufacturing process.

Thank you guys for the replies btw! Very helpful
 

k1ng 1337

Joined Sep 11, 2020
681
What do you mean by suspension?


Also, my criticism of wheel chair design was the seat is parallel to the ground. Just a 5° or 10° slope down to the back could prevent users from sliding out of the chairs. So many people sit in these chairs for most of their day - why not design with the geometry of a living room chair instead of the kitchen-chair geometry most seem to have. It's really sad that a design meant to roll someone from their hospital room to an x-ray was adopted as the design for people in nursing homes to sit in all day.
My cousin uses a manual chair with electric assistance and one time he almost went flying out of the chair going downhill. I managed to catch the wheel before we rolled down the cliff. Was the only time I felt like a hero in my life. All to say there is definitely room for improvement. I was skateboarding with him so you could also say we have a taste for danger. His chair is north of 30k too.
 

Irving

Joined Jan 30, 2016
3,133
Most power chairs are fitted with a lap strap/seatbelt. I rarely use mine, but occasionally off-road I feel the need!
 
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