Off-Road wheelchair for my wife

Hello everyone. First the back story: My wife and I were very active outdoor people, mountain bikers, camping, even our honeymoon was a backpacking trip in Yosemite. 18 months ago, at 7 and a half months pregnant with our first child, the lovely wife was involved in a rollover car accident that left her paralyzed from the chest down. (Number One Son was born that day via emergency c-section and is absolutely perfect. Wife refers to herself as the human air-bag). She can move her shoulders, biceps, twist and flex her wrists, but has no triceps or any hand control. She gets around these days primarily in a power wheel chair with joystick control.
Which brings us to the matter at hand. I am seeking help/advice in building her an off-road trike or quad so that we can enjoy the outdoors more like we used to. I am sure that there will have to be several prototypes constructed, as we are unsure until I make some test bed for her to drive, whether or not she can effectively steer this contraption with conventional style handlebars, or if we will need to use a joystick. This alone is a very fundamental issue, as it greatly affects the drive system; a single non-hub motor for conventional steering or two motors for differential speed steering like her power chair works.
I am throwing this out here for your collective brainpower to toss about. This is different then the usual topics here, and keep these characteristics in mind: "fast" will be at the most a brisk walking speed. It needs to have reverse capability. We have ventured, in a very very limited way down a couple of local trails in her power chair, and have learned that 3 (trike) or 4 (quad) wheel drive would most likely be very, very helpful in getting over tree roots, uneven ground etc. Cost is of course a factor. If you ever want to know just how much breaking your neck and spending 4 months in an intensive care unit might cost, I can tell you its well beyond 7 digits....
I envision for the first prototype that I will have a yoke that twists like bicycle handlebars for steering, but that also can be pushed forward and back for power. Hopefully this design will work for her, unsure about the strength and stamina in her arms to make this work over an hour or two trip, but we will see. If she can steer it with out needing two motors, that will simplify alot of things. Servo assisted steering? Adds complexity and expense on that end, but might make the drive system/speed controller simpler...
Anyway, I'll let this start here, and see if we can collectively put our heads together to make something viable... I thank you all in advance for your ideas and expertise
Dave

i have been a paraplegic since a motorcycle accident in 1992 spent 12 months in hospital
6 weeks in ICU Mega bucks i have been told, yet to pay a cent though, i had
no private health insurance, Medicare picked up tha tab!

So...i have seen several 'off the shelf' offroad trikes and quads ade for paras and quads
all are extrmely expensive. A local business here in OZ called Dreamfit are currently
working on something that would be right up your alley i think?
They are converting an offroad Segaway fo a customer, (whos a paraplegic)
They have made stabilizers so the client can transfer from wheelchair to Segaway
and a "T' bar arrangement for him to steer the vehicle...Might be worrth a thought
as the cost of standard "off road electric chairs" worked out around the same price as the Segaway INCLUDING the cost of conversion...Not sure if Darren has the info on the Dreamfit website yet
but google Dreamfit and have a looksee perhaps. If you need moe info Darren Lohman the CEO
is the most approachable, helpful and honest person i have met in my life i have
no doubt he would be happy to hand over anty info needed..

Best of luck to you and your wife..

KiM

I am thinking of something like a tadpole with non-steerable powered front wheels - two motor drive and two slightly smaller pivoting 'shopping cart' trailer wheels. This should not be a really complicated build. The quad approach is to avoid the frequent 'center of the path' nastiness that a trike center wheel will ride on. The recumbent should keep her in position while the two motor drive sidesteps the strength issue by allowing a joystick or similar for long rides. This clearly needs assistance to mount/dismount, but I think that may be a given anyhow.

If cost is a real issue, perhaps a local tech school could take on the fab for you as a semester project. Maybe a little local news story about the finished project and school to encourage them. Just a thought...

Guys do you remember those posts the last year... there was a tracked one and a 4 wheel drive quad, if I remember correctly. Perhaps we could find those old threads if someone remembers them as an idea bucket.

Found one thread: http://endless-sphere.com/forums/viewtopic.php?f=3&t=32863&hilit=offroad+quad

Here is a commercial one that might provide ideas: http://www.medicalmobilityinternational.com/store/wheelchair-power/4X4/ and http://ftt.free.fr/eng/quel/Quel1_eng.htm and some parts http://www.steintrikes.com/index.php

Tracked chairs: http://www.actiontrackchair.com/ and http://aac-rerc.psu.edu/wordpressmu...wer-chair-atpc-south-dakota-state-university/ and http://www.tracabout.com/ and http://www.crossbownation.com/forum/topic/10528-check-out-this-newly-designed-hi-track-power-chair/

Here is a guy making his own from power chair parts:
http://www.wheelchairdriver.com/power-wheelchair-off-road.htm

Here is a vendor of ATV tracks that could be modified into powerchair usage:
http://www.litefootatv.com/models/m3/m3-plus/ Below are two pictures of a robot built around a pair of these tracks. This bot could pull a 4,000 lb trailer with no problems at a walking pace.

Another possibility is a specialized version of a one of those cargo bikes where the cargo area is between the bars and the front wheel. These are often outfitted with kid seats - instead, outfit this as an open recumbent, etc and power it as a conventional ebike. This would get the wife on the trail fairly inexpensively, and make it easy for you two to chat. There are many of these to choose from and the mods should be simple and involve only seating changes - no drivetrain stuff since you would be driving normally.

As a major downside, this would not give her the fulfillment and personal independence of driving herself - which I'm thinking is very important....
Just thought I'd throw it out there though - sort of a funky bicycle built for two...

Hmmm - one way to make this more like a bicycle built for two would be for you to get the Plain Old Bike (and the ebrakes) and to give the wife the throttle - sort of like the person normally in back on a tandem who just pedals. An upside is that for relatively flat trails (rails-to-trails, seasides, or road biking) you would have conventional bike speed so you could see more scenery, etc. Since you would be at more normal bike speeds, you would not be an obstacle and could go on group rides to socialize if you wished.

DaveOtter and wife I couldn't read your post and not remark. What an inspiration you are to me and I am sure others on here. To react to such adversity in such a positive , proactive way is truly remarkable. Someday soon your son will know what wonderful, exceptional people are in his corner. The fact that you are on here looking for ways to enhance your wifes life warms my heart, as I hope I would only have half the courage to react as you both have. This makes me realize what we have taken for granted and what it truly means to be a strong person. I hope I wasn't out of line saying this but I felt like I had to. God Bless

Dean Kamen's iBot 3000 (an impressively expensive piece of gear) is the best gizmo I have ever seen for doing what you're talking about. I don't think anybody here can touch that product except with regard to raw speed, which carries drawbacks of its own.

But if DIY is part of the appeal, there was a run of Crystalyte one-sided hub motors a while back that would be a good starting point. I'd be tempted to use something that would fit inside of and bolt up to a Douglas ATV wheel, so as to allow the use of ATV tires.

Crystalyte is what we'd call a cottage industry, so upon special request they can probably make any of their hubs in a one-sided version for wheelchair use, with or without a disc brake interface that could be used to attach a wheel adapter plate for ATV wheels. The front wheel(s) could be from a wheelbarrow, hand truck, or whatever.

Having gotten a pair of suitable hub motors and wheels, the problem would become one of controlling the motors in a way that makes sense for your wife. You need direct drive because you need reversibility, but not all controllers support reverse operation. The simplest control would probably be "tank track" operation, with independent forward/reverse sticks for each wheel. The front wheel or wheels would be casters. The combat robot world is all over this kind of thing.

Thank you all for your ideas and well wishes. The last 18 months have been...an adjustment. We went camping for the first time post accident 2 weeks ago. More or less car camping, and with her regular power chair, certain things quickly became obvious. Teklektek suggested a tadpole/quad with a rear caster(s). Her regualr chair is what they refer to as a front wheel drive, with caster wheels in the rear. Works just fine around the house, in a department store etc. The casters really perform poorly off road however, as they can get hung up against rocks and roots that prevent them from swiveling around. I would like to avoid freewheeling casters for her off road chariot if at all possible. A low center of gravity is a must. Off camber trails with a high center of gravity and a narrow track width makes for a very sketchy journey. I had to hold her chair up once as she tried to negotiate a root on an off camber turn....nervracking. So my thoughts lean towards a recumbent position, with her knees bent, somewhat reclined, battery pack perhaps under her knees, keeping the CG low?
Bigmoose has pointed out the tracks that are available out there, and I bet one could go through mudbogs and over snow with those things! But not what we are looking for in this case. Tracks end up being much to wide for the trails we hope to go down, and they place the person too high. I almost said too high a center of gravity, but I bet those things weigh a ton, which is another problem all in itself. So tracks are out (but perhaps we'll save that idea for the next chariot)

Kim aka AussieJester pointed me towards this modified Segway. VERY intriguing....


http://endless-sphere.com/forums/download/file.php?mode=view&id=117294

Take a look at this product from the UK, the Boma 7
http://www.moltenrock.co.uk/wp/
http://www.youtube.com/watch?feature=player_embedded&v=uhmFpg4lB48

It very closely resembles my vision. The $15,000 price tag however is not in my vision... If I could build that, I think we would be pleased.

And just so you know who this is for...

DaveOtter said:

Take a look at this product from the UK, the Boma 7
http://www.moltenrock.co.uk/wp/
http://www.youtube.com/watch?feature=player_embedded&v=uhmFpg4lB48

It very closely resembles my vision. If I could build that, I think we would be pleased.

Click to expand...

Wow! Really nice product - besides all the electric drive/steering stuff, the off-road structural considerations like the rollbar seem well considered. I can see why this caught your attention.



Do you think that with two steering levers as shown above linked to move in opposing fashion she could steer unassisted using biceps alone, or does a power steering (assist) seem required? I'm thinking the latter, but just checking... (Four point X chest harness for her to pull against?)

Actually, my original thought had been for something similar but with the front/rear wheels closer together (almost touching ) and non-pivoting (tank) steering. I was thinking of no suspension but a bearing in the main boom so the front and rear axles could rotate in relation to each other to keep the wheels on the ground much in the manner of road graders and other heavy equipment. This would use simpler live (straight) axles in place of more complex independent suspension. But this Boma7 design with longer wheelbase and independent suspension certainly gives very desirable climbing and off-road capabilities - really slick.

Wow, what a story. I sure hope she gets some hand use back, so she can drive something better than stock wheelchairs.

I haven't thought much about wheelchair applications, but I have had this dorky dream of a motorized couch to take to a huge outdoor party.

The basic concept should work, and looks like what was used in that quad above. The key thing is make it skid steer like a bobcat loader or bulldozer.

Two very low speed winding hubmotors, then the joystick, or two sticks allow power to apply to each drive wheel independently. Make right motor go, you turn left. Make left motor go, you turn right. Make both go, you go straight.

A very very good thing to add, would be reverse. Then you can make one motor run forward, and the other backwards, and you get a spin in a circle with zero turn radius.

In the end, you get a zero turn lawnmower. Which brings us to... Maybe just buy her a toro, and remove the mowing deck? It won't go in very narrow places, but she could drive it on roads for sure. Gas power of course, but a gas motor can be replaced with an electric. For sure, the lawnmower has the transmission and controls you need. Mabye with enough mods, the mower can be made into something you can use.

Lastly, maybe it could be possible for her to enjoy nature more by using some kind of stable watercraft, like a small catamaran designed for fishing? Trails are tough, but cruising the lakeshore on a nice calm day could be a good substitute. Plenty of flotation worn of course, and you are right there with the kyack.

Check out these folks

http://www.steintrikes.com/index.php

http://www.varnahandcycles.com/cycles.htm

They both are into differently abled people and might help.
otherDoc

Located this description of the Boma 7 drive system - sadly, no description appears on the company site, but there are a few glimpses in the videos.

A super strong but lightweight chassis design made from motorsport rollcage grade tubing combined with all round independent semi-adjustable suspension and a powerful electric transaxle drive system with optional differential locking makes the Boma capable of climbing 1 in 2 slopes in some of the roughest of terrains without the complexity and battery sapping characteristics of 4X4 wheelchair design. Only top quality construction materials are used assuring reliability and longevity, plus repairs, if necessary, can mostly be handled by a local cycle shop

Click to expand...

...from here.

It appears from a vid/photo that the joystick model has a power steering unit installed.

FWIW - It doesn't seem ebike hub motors could address the kind of riding that the OP described or that is shown in the vids - the speeds are very slow and require substantial torque. At best something like a single sprocket wheel with a mid motor on the swingarm with a lot of reduction (Farfle - where are you? ) - perhaps one for each side to drive the rear wheels without the need for a differential and to get a little suspension. Otherwise some other application-specific drive (e.g. wheelchair drives). But - this is still in the vein of a complete custom frame/drive fab - a non-trivial undertaking.

On the bright side, power electric steering seems like it can be had as an add-on kit for ATVs - a quick search on Amazon shows many for under a grand. This looks like it could solve some strength/dexterity issues with no or minor adaptation. You might get away for less starting with a linear electric actuator, but the ATV systems seem like a quick means to get a unit that can be serviced in the future and has all the engineering tasks done up front....

=====

After seeing the Boma 7 - perhaps a less expensive approach would be to pick up a modestly-proced quadcycle (for instance: the Anura Quad) and retrofit a mid-drive motor and ATV power steering.



While searching about, I found this thread that has a Boma-like quad cycle that was custom built by Lightfoot Cycles for an accident victim. They don't list this particular bike but their prices seem good. If the price is right, this looks like a strong possibility for a platform. Since they are a fab shop, they could likely get you the bulk of what you need with one-stop shopping - (e.g. adding electric steering - custom length/width/seating height). Their build for you would have a few simplifications - no pedal assembly and no derailleurs (the one shown has two) since you could use a single cog in back. Mount up a mid-drive wherever it fits...

[youtube]7TjM788JK70[/youtube]

Anyhow - unless you have time and skills to spare, re-purposing all or part of some other small vehicle kind of looks like it may be the best means to eliminate a lot of design and test...

Teklektik, the ATV power steering unit is very interesting! I didn't know those existed, thank you for bringing that one to my attention as the notion of power assist is looming as possibly necessary, but the how was bothering me. I'd been thinking along the lines of a servo or linear actuator....I wonder what the average current draw on one of those is....
FWIW, I manage a sheet metal fabrication shop with a CNC laser, CNC punch, CNC plasma, press brake, shear etc. I draft in Solid Works and or AutoCAD and use those drawings to program our CNC machines. I also have a side job with a partner in which I TIG weld aircraft parts out of my garage as well as my own line of ultralight backpacking stoves, grills and cribbage boards. We don't have a mill or a lathe, but the guys across the street let me use theirs. I will build this bike from scratch as much as therapy for myself as it is a token of love for my beautiful wife

I liked the simple "suspension" of the ATC All Terrain Cycle. Allowing solid front and rear axles to articulate independently may be all that she needs for most situations, would be very simple to build especially for the prototype. I think I will build the first one that way, as it will be an easy, light weight and cheap way to keep most of the wheels on the ground. If it's not good enough, I can always build an independent suspension on the second version...

I have several power wheelchairs that were donated to us that I can cannibalize. They all have brushed gear reduced motors (with electric parking brakes) and joystick control. The problem with using the whole power chair drive train, with its twin motors for both drive and steering is the likely need to have the non-powered wheels caster, which I have mentioned that from experience, this doesn't work well. I could use a motor on each rear wheel, but power them together and steer conventionally with the front wheels.....

So, are direct drive brushless hub motors out? Not enough torque, but can they be ordered with special windings...oil filled to help with the heat of running so slow? I guess this is a fundamental question to get out of the way now, as it greatly affects the overall design. Hub motors, if they could work, open up a lot of very interesting possibilities, like very simple construction, switchable 2WD/4WD...

A guy I went to highschool with now rides this: [youtube]n8Y-CD4oIVo[/youtube]

Thinking about the Lightfoot Quad today.... here's a shot from the vid:



There are certainly many ways to press this into service, but here's some thoughts:

• The existing design uses two rear wheels and a single shifter to change rear gears. There is a transverse shaft to transfer power from the pedals to the wheels.The bike uses the familiar outside frames to support the outboard ends of the rear wheel axles instead of using a single-ended axle - uses common bike wheels.
• The functionality provided by the Boma 7 differential is instead provided by the Lightfoot Cycle rear wheel freewheels that allow the wheels to run at different speeds when turning. The Boma 7 uses a lockable differential to allow running in the snow or where one wheel would spin w/o traction. The Lightfoot design provides an equivalent functionality without the lock - the wheel with no traction cannot turn faster than the wheel with traction.
• The 'OtterBike' needs the functionality of the Lightfoot cycle + reverse capability - which doesn't work in the existing design because of the freewheels.

A possible way to modify this is to:

• Remove the pedals and transverse shaft.
• Remove the derailleurs and swap out the rear wheels for front wheels with disk-ready hubs.
• Stretch the outboard frames about a foot forward and weld two drop-out mounts on top to allow a gear motor to be dropped in, positioned in front of the wheels (sort of like the motor-in-the-swingarm idea).
• Mount sprockets to the motor and wheel hubs using the disc brake mounts and with something like a 2:1 - 4:1 ratio to get the vehicle speed down to 8 mph max. With the internal gearing, this will be something like an overall 5:1 x 3:1 = 15:1 ratio so the motor should be running pretty nicely with good torque at very low speeds (without melting).
• Use gears motors like 350W or 500W MAC (heat dissipation for a bit of crawling suggests a bigger motor than needed for cruising) and weld up the freewheels in the gear clusters converting the motors to geared DD. This should also let them drive backwards and be able to give some motor (regen) braking for descents.
• Use disk brakes only on the front - no rear brakes - use the motor regen there - with a 1:15 gear up, the motor drag should be pretty good with two motors.
• Power both motors together - not for steering, but for a 'pseudo-limited slip differential' effect so the bike can turn and can transfer power if one wheel loses traction.

I think this is arguably a simpler fabrication than the existing pedal assembly, transverse shaft, derailleur, and dual shifter approach - just lengthen the outboard frames and weld on the dropout tabs. This should save a bit of fabrication $$. The dual small gear motors may well be cheaper than a good quality mid-drive (? out my element here). With dual motor/controllers, there is a nice limp-home mode on the remaining motor if there is a failure out on the trail.

DaveOtter said:

I envision for the first prototype that I will have a yoke that twists like bicycle handlebars for steering, but that also can be pushed forward and back for power.

Click to expand...

One of the ads for ATV electric power steering talks about being able to drive a big gas ATV with one hand - that seems like it will work out nicely for this lighter and less powerful vehicle with a yoke like you describe. A custom or off-the-shelf '5K pot-box' could substitute for the throttle to run both motors - connected to the yoke with a cable so the front/back yoke motion pulls the cable to work the throttle. The old style analog Xlyte controllers have a reverse switch and drive gear motors very nicely. Hook them up to a FWD/REV paddle on the yoke or rig with the yoke fwd/bkwd motion.

If Lightfoot can build up the basic frame with the ATV steering assist mounts welded up and the wheels mounted (basically a rolling chassis) then you might add the motors, seat, and yoke yourself or locally. This should cut the fab cost and depending on your skills, let you do the non-welding part of the build to save some bucks.

Anyhow - just some thoughts...

An alternative way of going offroad how about 4 up to 8 wheel drive with skid steer, steering could be 2 standard throttles with an upright tube clamped to them to allow twin joystick steering.
These motors are brushed and geared so control for skid steering should be easy with just to high powered reversable speed controllers, plus it takes care of reverse.
8x 12" wheels should basically give you an equivalent to tracks but low cg and width.
Go to wheel chair page at bottom and hub page anbout half way down. http://www.goldenmotor.com/

There are cheaper ones on the usual Chinese sites but these were brushed which I think will make control simpler plus they have parking brakes.

Alternative cheaper way
http://secure.oatleyelectronics.com//product_info.php?cPath=116&products_id=810&osCsid=p97gm624n46u3rc538sl96gs07 weld up the free wheels

add asmany wheels as you want and use chain drive from a pair of these
http://secure.oatleyelectronics.com//product_info.php?cPath=53&products_id=942


Main drawback is the chain drive could be messy and a possible failure point although easily fixed with a chain breaker. prices for similar item in the US would be cheaper.

Basically a downscaled version of this.


Good luck.

DO-
Oops - I typed up the last post on and off in bits and pieces over some hours and missed your post that went up while I was at it... Dunno how I missed it during 'preview' but ...

DaveOtter said:

...the ATV power steering unit is very interesting! I didn't know those existed, thank you for bringing that one to my attention as the notion of power assist is looming as possibly necessary, but the how was bothering me. I'd been thinking along the lines of a servo or linear actuator....I wonder what the average current draw on one of those is....

Click to expand...

I have no experience with these at all - they just popped up when I searched for electric steering stuff. The images seem to show a small gearmotor device that replaces the stock steering box and should hold position - so I'm thinking that it will probably draw as much power as an auto wiper motor (maybe 12v x 6A or so) but only while positioning. Just a guess.

DaveOtter said:

FWIW, I manage a sheet metal fabrication shop with a CNC laser, CNC punch, CNC plasma, press brake, shear etc. I draft in Solid Works and or AutoCAD and use those drawings to program our CNC machines. I also have a side job with a partner in which I TIG weld aircraft parts out of my garage as well as my own line of ultralight backpacking stoves, grills and cribbage boards. We don't have a mill or a lathe, but the guys across the street let me use theirs. I will build this bike from scratch

Click to expand...

I see that you have better than average fab skills and equipment, and plan to fab this from scratch - so, ignore a bunch of my last post. I was going for a basic buy-subsystems-and-assemble approach for a guy without your resources... Part of the idea was to use more or less common parts so there was little really custom work and not much cutting and fitting kind of stuff - simple future replacements, etc. In your case, you could certainly go for a more elaborate drive system, etc since you can fab/fit/position all the stuff as you go. Since you will be fabbing the chassis, etc, then you might go with single-end mount rear axles, etc.

DaveOtter said:

I have several power wheelchairs that were donated to us that I can cannibalize. They all have brushed gear reduced motors (with electric parking brakes) and joystick control. The problem with using the whole power chair drive train, with its twin motors for both drive and steering is the likely need to have the non-powered wheels caster, which I have mentioned that from experience, this doesn't work well. I could use a motor on each rear wheel, but power them together and steer conventionally with the front wheels.....

Click to expand...

As you can see from my last post, this 'conventional steering with two motor drive' idea was sort of the direction I went in - largely from your desire for a Boma-like vehicle. There will still likely to be some tire scrubbing for tight turns, but this might not be too bad. It could be mitigated either electronically or mechanically by unbalancing the rear wheel power when you turn. For instance - a non-electronic solution might be something like this: Looking at the 'dual hub controller, single throttle pot-box with cable' strategy sketched out in the previous post - suppose instead there were two pot-boxes - one for each motor. If both of these are activated by cable pulls that go straight back from the steering yoke, then both cables move the same as the yoke is moved forward or side-to-side. But if the cables are angled out to the sides from the yoke (maybe 20 degrees) then the cable pull for the two motors depends on the direction of yoke motion: push the yoke forward and both throttle cables pull the same, but push it forward to the left, and the right cable pulls slightly farther giving slightly more throttle to the right outside wheel. (That's the 'yoke as airplane joystick' example, but similar things could be managed with a turnable bicycle handlebar motion.)

Some equivalent effect might be had electrically for a stock wheelchair joystick - perhaps by driving an Arduino processor with one or two pot-boxes to detect front/back and left/right yoke motion. The processor maps the pot-box inputs into appropriate joystick resistances and drives a couple of digi-pots to replace the 'real' joystick pots of the wheelchair motors (just trying to do this as an isolated front-end pre-processor interfaced through the joystick rather than digging into and re-engineering the wheelchair control system). This gets you forward/backward motor control and a bit of dual motor power skew for inside/outside wheel speed differences. The ATV electric steering would just work separately and normally from the yoke. Dunno - lots of ways to go after this...

• EDIT - Actually - an easier solution might be to replace the wheelchair joystick fwd/rev pot with a pot box with equivalent resistance and use another low resistance pot-box and a few resistors to replace the wheelchair side-to-side pot. This would give only a small power unbalance when turning (low resistance = maybe 5% of total chair left/right joystick resistance.)

DaveOtter said:

So, are direct drive brushless hub motors out? Not enough torque, but can they be ordered with special windings...oil filled to help with the heat of running so slow? I guess this is a fundamental question to get out of the way now, as it greatly affects the overall design. Hub motors, if they could work, open up a lot of very interesting possibilities, like very simple construction, switchable 2WD/4WD...

Click to expand...

Yep - I'm the wrong kind of Engineer to give a good analysis on this - another more knowledgeable member would need to step up. However, from a shade-tree gearhead perspective and Justin's simulator, it looks like for the speeds you are talking about, you are way out of the efficiency range of the hubs and most of your power is going straight to heat. The gearmotor-chain-drive proposal above was just a sleazy idea to get the hub up to a reasonable rpm range without using the usual jackshaft, etc of a mid-drive configuration. FWIW - I have seized the clutch (freewheel) in my gear motors many times and run them for many hundreds of miles as 'geared DD' motors until I replaced the clutch. No problem. The only minor issue was a slightly deformed key on one clutch/gear cluster assembly from the bi-directional torque (the freewheel normally limits force to one direction). Replacing the stock key with one of a less malleable steel should prevent that. MAC gears are astonishingly rugged and should give you very very long service if you go that route.

But, since you already have wheelchair motor drive systems in hand, instead of using the proposed hub gear motor approach, you might just mount up your wheelchair drives and chain them up to the larger wheels/tires. You could go direct drive as original, but a chain drive would let you fiddle the ratio and perhaps get more flexibility in wheel/tire choices. If they are powerful enough to do the job for the terrain, this would get you a nice rugged package with minimal fabrication. You already have the control system, so this could look pretty nice. It also gets you the electric parking brakes for free, which is a nice bonus.

BTW - sprockets that bolt up to disk brake wheel mounts seem to be an off-the-shelf item which is why I went with front wheels for the rear...

There is an ES member, JRH, who is an excellent wheelbuilder. He might be able to either advise you and/or lace up wheels for you. You will likely need smallish wheels that can take a bit of side-force (at least at the rear if there is scrubbing). The Lightfoot Cycles bike had pretty big wheels (26"?) and I'm thinking something smaller like the Boma wheels are more desirable.

Anyhow - just some thoughts that may or may not prove useful...

Update - I just ran accross this YouTube from 2009 - an earlier Boma design using hub motors with an outside axle support. Not only of historical interest but reflects on some of the discussion above (two rear wheel drive + front wheel steering) and has an interesting over-the-top sheet axle support instead of the more familiar horizontal outer frame approach....

Actually a pretty cool little rig but the slow speed on the climb has got to be raising havoc with the motors - good thing it's a short staircase...

[youtube]QylyfA6kM9Y[/youtube]