PogesKnows

Hi all,

I don't know too much about bikes (or in this case trikes) but I thought maybe some bike enthusiasts might be able to help me out. I am an undergraduate senior in biomedical engineering and for senior design my team is attempting to build a pedaled wheelchair (bear with me on this one). For stroke patients hoping to recover from partial paralysis or elderly patients, it has been shown in various tests that a pedaling exercise can rehabilitate patients, hence the pedaled wheelchair. The product could also be targeted for the elderly who may have trouble walking but may have better ability pedaling a wheelchair to get exercise.

We are modifying an existing wheelchair by adding a pedal system that can be stored beneath the chair, that then uses a chain driven system to drive an axle between the back wheels. The problem we have run into is the turning. The turning system will work by using two brakes, one on each wheel, to turn the chair. But to do this, the rear wheels must turn independently. We are hoping to find rear wheel differential to take from an existing product and use for our senior design project.

We thought that our best bet would be to try and find one on an adult tricycle system (one of my teammates found a patent for one at some point). I've put out some feelers to different companies but in the mean time I thought I might ask elsewhere. Does anyone know of any adult tricycles that use something like this?

Thanks for any responses!

Bill Kapaun

Would it not be easier to take an existing trike and modify it to fit your patients?

PogesKnows

The reason we want to use a wheelchair system is so they can use both a traditional wheelchair, by stowing the pedal system, and the pedaled system. The current pedaled system on the market does not allow for this and patients knees are kept very high up due to the pedal system. Because of this they need two systems, the pedaled and the non pedaled. We're looking to combine the two so the patients won't need to switch systems if they want to use the pedals, they'll just use the linear actuator system to bring the pedals out and then go back to the hand moving system when they are done. This also lets them pull up to a table, which current systems do not.

Hope that helps!

dsbrantjr

LMGTFY

HillRider

One approach is to drive just one rear wheel and let the other one turn freely.

xenologer

You'll probably need to look elsewhere. Say, electric golf carts.

Adult Trikes don't use differentials.
They just drive one wheel (usually the right one) and let the other side freewheel.
Similarly, they only have brakes on 2 wheels -the front, and the Driven rear wheel (one side only).

also consider:
Recumbent Tadpole Trikes, which use 1 large wheel in back, and 2 small wheels in front. Also avoid the need for a differential, since only the single rear wheel is driven.
They then have various braking configurations, one of which is to have separate brake control for each of the 2 front wheels to enhance steering. Tho others control both front's simultaneously with the rear wheel separated...

Maybe you should consider a Tadpole wheel configuration? it works for Trikes, avoids the complexity of a differential

Andrew R Stewart 

Adult trikes have very much has proper differentials for decades. That most don't today is more a factor of economics then design. Schwinn used such for years. Another configuration is to have both rear wheels driven by freewheels. These are driven from a common shaft. Andy

Jeff Wills

The Samagaga differential is used on a couple high-end recumbent trikes: SAMAGAGA

As Andy pointed out, Schwinn trikes used a differential on their adult trikes through the '70's and early '80's. They were made by Ret-Bar (I think) but Ret-Bar is long-gone.

HillRider

Yes, but you have to find a freewheel that works "backwards" for the left wheel since a standard one would freewheel the wrong way on that side.

Andrew R Stewart 

That's assuming that you mount the LH freewheel on the wheel's outside. Also note that BMX bikes (or is it really called street bikes, I'm out of touch with the 20" trick stuff) have LH drive available. Andy

dabac

Last I checked, "lefty" BMXes weren't that hard to find.

HillRider

OK, putting the freehub/freewheel inboard is a possible solution. As to the BMX stuff, I've never been in touch with it so I wasn't aware they were available with left-side drive.

Retro Grouch 

I don't think that you have tried very hard to research this yet. They're out there.

PogesKnows

Thanks for all the responses! We actually managed to find the samagaga website late last night, although it took us a little longer to find a website selling their products directly. We think we were able to find what we were looking for. Thanks again!

MichaelW

"Famous" British tricycle builder George Longstaff solved this riddle to produce two wheel drive trikes. He didn't get rich through this invention. It is a useful search term to locate the way he did it.

AlexCyclistRoch

Oh, of COURSE not; this is a student project, after all!

I remember my graduate project for my BSME: We stayed with inexpensive steel, ALL the other teams blew their budget on aluminum and other fancy frippery. In the end, our design cost 1/4 what other team designs cost....

wesmamyke 

Seems like you got some good replies there. I'll leave mostly because it interested me when I read it. Somewhere on the web is a page about a wind/propeller powered trike, I think the one that drove into the wind faster than the wind speed for the first time.

They had a pretty good rundown of the mechanical bits. The "differential" on the back wheels was the guts from large industrial ratchets, as they have a built in switch to reverse the direction. IIRC they were actually outboard at the axle ends or in the hubs themselves.

curbowman

You should look the Hase trikes. Both the Hase Kettwiesel or Hase Lepus are delta trikes (two wheesl on the rear, one on the front) and they use a patented differential that houses an articulated joint, to provide torque to both wheels even if they have a pronounced camber angle. The Samagaga differential works only on parallel wheels.

Trike ? E-Bikes, Recumbent Bikes, Handbikes
Recumbent Bike KETTWIESEL KROSS ? E-Bikes, Recumbent Bikes, Handbikes
https://hasebikes.com/files/anleitung...abe.pdfHowever, it should be noted that having two wheel driven in the rear is not really necessary if the wheels are on solid floors or pavement. Usually, having a single driven wheel with a freewheeling one is enough. That's why Samagaga also provides an "easy turn" gear system.

SAMAGAGA

BTW, Hase trikes have always had lots of options for special need riders. People with some degree of spasticity can benefit more with a 'fixie' (where the drive wheel has no freewheeleng capabilty), as seen below in their story about Sammy:

“Because of his spasticity, he wasn’t able to ride a standard TRIX with gears and a freewheel – he can’t pedal consistently. We had them equip the trike with a fixed gear and special pedals with calf support. Now, riding is a piece of cake.” Without a freewheel, the pedals keep moving as long as the trike is in motion, even if Samuel loses his pedaling rhythm.

Full story here:
Special-Needs Trike TRIX ? E-Bikes, Recumbent Bikes, Handbikes

Flyinggate1946

I have several Trikes

One Wheel Drive, for me this works well. Cons; turns better on LH turns, RH turns require a stab of brake mid turn. Wheel spin on wet assents. I am assuming your wheelchairs will be going a lot slower than my 18 MPH average and this system would be suitable

Higgins / Longstaff Dif. is a diff in the true sense of the word. complicated and expensive.

Trikit system: This incorporates a journal that has threads for a Shimano or Campag cassette to be screwed on Internally is a each axle is connected by a freewheel (gear and pall) So the drive is taken over to the outer wheel of the corner either directection

Geoff Booker also makes conversion sets (Bikes to Trikes) one of these could be adapted for your needs.

I would go for the one wheel drive.

maddog34

you've never moved around by wheelchair, have you......
it would just spin in a circle with one wheel drive....

the OP would be better off to use a ratcheted limited slip of some variety.... and the inside wheel of the chair will lose traction in any sharp cornering... WC's are kinda top-heavy....

Also... check with some WC racers for inside info... and also hit up the Recumbent and adaptive cycling forum on this page...

i've had some experience with wheel chair mobility... and those electric chair trikes too...

build a single rear wheel trike... no differential needed... use a bmx sized fat tire at the rear, and two 12 1/4" wheels in the front.. and you'll need to steer the rear wheel somehow... or both front wheels...

jimbo.

I'm thinking that a chain drive would be messy. How about a lever and rod system. Power on the push. Not a rotary system. That way each wheel could be powered independently. Have I ever seen a rowing bicycle kind of thing?
You have to think outside the box on this one.

fietsbob

Already done , German Delta Recumbents.. probably hate the price ..

fietsbob

that is how most adult trikes work , chain drives a shaft..


one hub uses its bearings, the other is fixed to a flange with pins to match the holes in the hub.

the 2 rear wheels are the same.

FBinNY 

The simplest way Basedown on your basic design, is to use freewheel hubs in both wheels. This has 2 benefits.

1- if both wheels freewheel, you have normal rim drive without engaging the pedal drive train.
2- you have a differential, of sorts since the outer wheel can overrun the inner on turns,

The drawback is that rolling backward is problematic.

The other option is a fluid or friction clutch in each wheel that allows some slippage under torque loads. This will solve the turning problem, but will probably slip a bit during acceleration.

The most perfect, though over engineered solution would be magnetic clutches for both wheels. These would be normally engaged, but either would automatically disengage then that brake is aplied. Of course, both would be disengaged for normal rim drive use.

nfmisso

Another direction:

100 Series Differential with 1" Diameter Axles

ATV Differential | eBay

https://www.searspartsdirect.com/par...EaAgC2EALw_wcB