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wheelchair power assist
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andrew



Joined: 16 Jun 2004
Posts: 3108
Location: Castle Hill, Sydney. N.S.W


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wheelchair power assist

Thought i would engage you all in pondering ideas.

My partner Kristy has a degenerative knee condition and is getting to the point where shell need assistance to get around. Luckily my work is in building wheelchairs.

Today she came to work so myself and a therapist could script her a badass manual wheelchair (titanium frame, light as all hell). Going to be some getting used to driving the thing but one issue i see is mild hills and such. She doesnt have the muscle strength yet to get up them.

The chair when we get it in 2 months time will be a few thousand bucks so i dont want to chop and mod it much but i saw an item which clips on which works well
http://www.seatingdynamics.com.au/161/SmartDrive.aspx

This item is easily about 6-7 grand but it got me pondering on various things i can maybe make externally to the chair to attach as a remeovable item using hobbyking parts.

Now one setup is a little hinged wheel pod i can secure to the camber tube (between the rear wheels) made from brushless motor geared down driving a medium size colson.

My minds got lots of little projects i can look into to maybe assist her (another being chopping a bike up and making a hand cycle attachment) but thought i would ask all you much more intelligent peoples on thoughts.

I have an old klunker of a manual chair we use now that i push her around in when we go out which will be modified to have power wheelchair parts shoved in it for some fun but a compact, slow speed high torque lightweight and preferably cheap option would be awesome considering this chair will be easily 3 grand of money i dont have (luckily works helping me out and im paying it back over time at mates rates compared to normal)

Thanks for any ideas.
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Post Wed Sep 18, 2013 11:53 pm 
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miles&Jules
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Joined: 19 May 2010
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Location: ipswich QLD


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Hey Andrew ...that add on motoized thingy looks cool....so it just gives extra force and you still steer by the regular wheel chair wheels?

You could use a winch gearbox with a brushless on the back...those things can push anything....the gearbox of the winch weighs less than 1kg cause its mostly ali.....so would be light enough...then just power it with a lipo and esc and servo tester for power....the hardest part would be making the wheel mechanism nice and tidy i guess.....should be fun to use robot building skills for a real life helpful purpose...cant wait to see what you do. Very Happy
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Post Thu Sep 19, 2013 12:11 am 
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andrew



Joined: 16 Jun 2004
Posts: 3108
Location: Castle Hill, Sydney. N.S.W


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thats actually a real good idea, how much is all that setup

Aaron may be able to assist as the weopon setup from farm boy is fair perfect or if he needs some extra money i can buy it off him Smile
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Post Thu Sep 19, 2013 1:05 am 
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miles&Jules
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Joined: 19 May 2010
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Location: ipswich QLD


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I'm stealing that setup off him for Kojack ....for the nats first though he he.
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Post Thu Sep 19, 2013 8:42 am 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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I'm really sorry to hear about Kristy; my dad had something similar so I know how difficult it can be.

The Smartdrive is really clever; after looking at the videos, it looks like a clone will need a micro controller and sensors to work like the original device, or an easier option would be an accelerator pedal and steering by manually braking one side.

I am not sure a Colson wheel will work so well; the Smartdrive has an omni directional wheel to steer around corners, while a Colson will want to go straight ahead. In tight corners, the Colson would be pushing at up to 90 degrees to the direction of travel and could stall or maybe even tip the chair over. If the omniwheel is the "secret sauce" to this product, finding one or making one is a top priority! There are heaps of Asian manufacturers turning out omniwheels; I found these links in just a few seconds:

http://www.alibaba.com/product-free/136588504/203mm_double_aluminum_omni_directional_wheel.html

http://www.alibaba.com/product-gs/880127834/152_4mm_double_aluminum_Omni_direction.html

They don't look super high quality but the price is right!

If you go with a winch gearbox (great idea Miles!), its going to need some way of disconnecting when it is not actively pushing the chair or it will act as a giant brake. Perhaps the drive wheel could be lifted or an electronic clutch can release when the motor isn't powered...

Post Thu Sep 19, 2013 9:58 am 
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andrew



Joined: 16 Jun 2004
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Location: Castle Hill, Sydney. N.S.W


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worst case all good ideas.

I can rig up a servo tester unit on the armrest she can just turn on when needed or a push button style thing

Its only for hills, will be Very slowwwww and will only be used for a few seconds

pondering having it on a swivel so you only drop it when needed sorta thing or drops when turned on and raises when off or something also

The smart drive is great but i want something she can control
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Post Thu Sep 19, 2013 12:13 pm 
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miles&Jules
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Joined: 19 May 2010
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Location: ipswich QLD


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yeah Nicks right you would need some way of disconnecting the drive for regular human pushing.....what about a pin through the shaft that you could put in when you need it to use the motor. Though that would be difficult for the person in the chair to do.
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Post Thu Sep 19, 2013 12:28 pm 
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Valen
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Joined: 07 Jul 2004
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Location: Sydney


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I'd be thinking about something that clipped onto the main drive wheels something like a spider coupling into the spokes.
Have an arm that comes from the back nice and low for the torque and to give free access to the rims. Fewer moving parts at least then.
Some kind of sensored brushless motor and a clutch would be my pick for drive.

If the drive is just regular "power" drive she could tweak the direction by just manually breaking each wheel by hand.
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Post Thu Sep 19, 2013 12:31 pm 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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Here is another site to grab some ideas from: http://www.rubbee.co.uk/

The Smartdrive and this Rubee are made to fit many different vehicles but with something you make for Kristy, you just have to fit one chair so you can take a lot of short-cuts. If you went for friction drive, you could either have two motors and a joystick steering, or you could have one central motor with a diff and steer by hand braking one wheel or the other.

I think we all understand the the motor / tank steer method better, but the single motor option would probably be cheaper. Either way, I keen to help build something!

I agree that a sensored motor would be the best technical solution, but that puts the price up compared to Hobbyking parts. With the huge chair wheels and the low speed needed, a brushless motor will need massive gear reduction, so its probably going to work OK without sensors.

Talking of gearing, what's the size of the chair wheels and the reduction in the winch gearbox?

Post Thu Sep 19, 2013 1:06 pm 
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andrew



Joined: 16 Jun 2004
Posts: 3108
Location: Castle Hill, Sydney. N.S.W


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chair will have 24 inch wheels

I want it to be an option and not converting this thing into a power chair

As in manual chair and option for assist up hills if going to an area with hills

Im thinking aarons idea of brushless in winch drive gives roughly rpm im after, light weight and i can make up an attachment system where it clips onto the camber tube if needed and its just running a push button switch to side of armpad or something


I need to do alot of thinking and will be able to progress with it once i have the chair but lots of interesting ideas
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Post Thu Sep 19, 2013 3:25 pm 
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Knightrous
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Joined: 15 Jun 2004
Posts: 8469
Location: NSW


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The 2000lb winches are what you want (they have the Raiden labels on the gearbox), they have a single stage (sorta) 153:1 reduction. The pinion for the gearbox input is 1 piece with the armature shaft so you have to cut the motor shaft up to use it (wasting the motor!). Get someone with a precision lather center drill setup (Nick?) to do it, the one I did was a fraction out on my C6 lathe and I had to make a floating mount for the motor, because it wobbled and made the setup noisy.
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Post Thu Sep 19, 2013 4:08 pm 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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Yeah, I can definitely do that. I have the right reamer to get a good solid press fit on the new motor shaft as well.

Post Thu Sep 19, 2013 4:13 pm 
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Knightrous
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Joined: 15 Jun 2004
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Location: NSW


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Alternatively, would a pair of cordless drills with grinder boxes on them provide enough reduction? Could basically hold a drill in each hand, clip them into the wheel hub on each side (with a small mount to take the torque load off the human) and control them with the variable speed triggers for driving/steering/reversing. Provides a simple way to charge them and they would be small enough to throw in a backpack when not being used.
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Post Thu Sep 19, 2013 4:13 pm 
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Nick
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Just doing some quick maths; Using something like a Turnigy Rotomax 1.2 with a KV of 280, 153:1 gearbox, 22.1V Lipo and a 26" wheel, the no-load speed is around 4KMH. That sounds about right if its just for short bursts up hills and the motor is rates for 30V so you could get it going faster if needed.

Post Thu Sep 19, 2013 4:26 pm 
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maddox



Joined: 21 Dec 2006
Posts: 758
Location: Belgium


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Nick, the Rotomax 1.2 is a 2kw motor (peak of course), so we can assume it can put out 660W for a long while without overheating.
This is on par with the power of a normal "outdoor" wheelchair. (2*300W)

The NTM 50-60 280 KV is in the same powerrange.

A brushless outrunner motor in the larger size and 280 KV range, a 6S pack , TZ85 and a servotester combined with a 24-1 gearbox and the 203mm Alibaba omniwheel could do the task , and keep the pricetag below a grand.

For added comfort, add a small linak and a spring to the setup, and pull the "spring loaded" wheel up with the flick of a switch.

Post Thu Sep 19, 2013 6:38 pm 
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