Honest this is not a Joke - this is the design brief for the engineering students at the college where I work. They have to build a wheelchair that is capable of going off road i.e coastal paths etc and also be acceptable on the pavement. its going to be battry powered and use solar panels and/or an alternator/very small motor for recharging purposes. Max speed 8mph but it can always be restricted. It will be based arounf the original classic wheelchair design and the students allready have 3 wheelchairs, solar panels, batteries. basically its to help the severly handicapped get out in to the countryside.

Any suggestions for ideas in relation to suspension, wheels, tyres, rollcage, motor, charging, design concepts are most welcome

Forgot to mention this is for an educational competition and forum/supporter stickers/references are most welcome and will be advertised on the vehicle.

Again in all seriouslness.

You'll need to think about

• Stability - wider = more stable
• Some form of suspension
• Some form maybe of a simple lock diff for not getting stuck

One possiblity would be to look at say 'quads', and battery power it & reduce size weight. ?

Nige

Interesting. Some thoughts:

1. I'd be thinking more along the lines of a 4-wheeled motorised mountain bike. Keep it light and simple.

2. Wheels - seriously think about mountain bike or BMX type tyres / wheels. The larger radius is useful offroad, you have plenty of torque from motors. Brakes are of course already there if you need them (probably not if you are trying to regain energy from inertia). - On second thoughts, you'll need brakes anyway, won't you.

3. I'd think twice before using solar panels. Its ok for keeping a stationary car battery topped up, but for actually charging you'll not get much out of anything that fits on a wheelchair. Without ensuring they point at the sun and spending a small fortune on good quality arrays, I think the weight and complexity issues will outweight the gains. Work out how far it'd drive the chair after an hours charge at realistic efficiency for cloudy English weather, off-angle charging etc (15% efficiency?). I'd be surprised if its justifiable.

4. If its just for outdoor paths / walking routes, I'd keep the suspension pretty small and light. Something like a bicycle rear shock has it all built in. You could make your own with a little machining if part of the brief is to not use commercial parts. Just a little spring and dashpot. You're not putting it on an articulation ramp. Design of ability to flex depends on steering system / drive mechanism, which we don't know yet.

5. Keep the batteries and system masses low down in the chassis. You don't need uber-clearance, or portals or anything like that. Its more likely to need to be lifted over a style than drive over boulders I guess, so mass is probably more important than clearance to some extent, and you don't want it flopping on its side, so stability is key too.

6. If you must put a roll 'cage', just go for a single simple hoop. If it does flop over in 'roll' (in terms of aircraft axes), the moment of inertia should be pretty small about the pivot point if you managed to follow point 5, so it won't see too much force. Shoot for 1 or 1.25" steel tube max, and if you decide to brace it, run cross wires (small diameter steel cable) that brace in tension only - much lighter. Safety belt? Bucket seat & harness for support?

7. You might want to consider the seating posture. Those foot plates make for crap clearance. You want the seat base as low as is reasonable to bring the CoG down, and the feet as high as possible (without inverting the occupant!) to keep clearance. Exactly like designing an offroader chassis - keep the high bits low and the low bits high. To me, this is suggesting something similar to one of those recumbent bicycle type postures. Maybe.

8. Forget 4wd or anything like that. This thing isn't going to get used on its own, and people can always push if its struggling. With a motor for each rear wheel, you'll not need axles / diffs etc. Maybe its lioghter to use one though (more energy efficient too?).

9. Bling the crap out of it. Wheelchairs look crap, and I've never understood why people don't put a bit of life into them.

Hope it helps, good luck.

Al.

Recognising we are just tossing ideas about, not completing a full design in 5 minutes.
Most vehicles (I've seen) for disabled people don't have the rider astride the vehicle, presumably this is a mount / dismount issue. Thus I'd say look at mobility scooters as a design basis.

I'd also go for very big rear drive wheels (motorbike wire spoked, to prove the design?) with a deep sidewall, these would be better to ride / drive over rough terrain, and with suitable tyres (I'm not sure where from, sand tyres perhaps) might do away with the need for suspension, and it's weight disdvantage. Because of the diameter and the need to give elbow room without snagging them in the wheel, the rear axle would be pushed further back, increasing the wheelbase. This would give more stability on gradients, which is a positive move, IMHO.

You will appreciate there are already commercial 'off road' wheelchairs / mobility scooters. Somewhere I've seen reference to an organisation that puts two or three in a covered trailer, delivering them to car parks for people to use.

HTH

why not go for a three wheeler with two wheels at the front and one at the rear. it will lead to a very stable vehicle that people will feel comfortable sitting in- wouldn't you feel uncomfortable in a wheel chair if one wheel kept lifting? Also you could think about just powering the rear wheel- as it would never leave the ground you would never lose traction.

Both of my grandparents have 'large' off roading mobility scooters, there not bad but basically they are standard scooters with big pneumatic wheels and uprated motors, they happily drive along the beach and car crawl up 6" kerbs without too much hassle.

A point to make, if your thinking of off roading them, you need GOOD hill decent control, my granny recently ended up in hospital after laying her self all over a main road because she lost control of the scooter going down hill on the pavement! I might add she is neither light nor agile which will have played a huge part in the accident!

Ideally makign the thing wider would be idea but you have to look at a huge number of size related issues. Most if not all scooters are designed to fit through a normal open door way (which is around 700mm wide), they are designed to be light enough for your average person to pick up (say 40kg ish between two people) and they have to be compact enough to go in a car/van (how else do you get to the off road walkways). You'll also have a huge issue with access, most coastal walk ways that i can think off have gates at either end to stop animals getting in/out (maybe i've spent to long in wales?).

Oh, go have a look in the NEW highway code and there are now rules about the use of mobility scooters on and off road (mostly speed limits etc) but i think these relate to new additions to the road traffic act (the highway code links to all relevant sections of the RTA).

Sounds like a birlliant project though!

Have a look a s sports chairs, their drive wheels have a serious load of negative camber so they have a wide track at the contact points with the ground but are not too wide above. Think about the weight of the chair with everything on it plus the user and consider where it needs to be able to go. It will probably be too heavy to be lifted over things. You should aim for large diameter wheels and also big tyres for flotation and traction. The wheel chair marathon chairs are a great design with good ground clearance. They are long for speed stability but can be shortened for off road use. Make a model and see if front wheel drive with trailing casters might be better. Also think about the extreme options too. Overall tracks around a large wheel to a small wheel, either leading or trailing, that can be fitted in really difficult ground. Don't bother with recharging with PVs as it won't work. A large enough PV array would be better used as a sail or a wing then battery charging. Better to look at Li-Ion batteries (lap top batteries) and put the money in to those. Also consider the gear ratios used.

Test models, lots of them. You can make them out of lego technic. Think about how a conventional single axle, two wheel drive chair with casters would cope when one wheel is against a small rock and it is trying to drive over it, it ends up skid steering around the rock.

Great project, I wish I was on board with this.

Or you could look at how the professionals move a load across rough ground and base your project around a modified powered, tracked loader like this. The barrow could be removed and replaced with a secure seat and roll cage, the controls could be modified to be worked by the user or by remote and the Honda petrol engine could be replaced by an electric system. You could design the vehicle to carry a range of wheel chairs within a cage or a fitted seat depending on the user needs.

It would be my prefered choice of off road wheel chair.

Looks like someone has already had a good stab at this (impressive videos too) IBOT 3000

hope the students aren't accessing this site, they are only supposed to get a design brief, not all of this expert knowledge.

what college you at?

Were you thinking of something like this?

My partner, who has spina bifida, has used the previous version for several years now. Only the rear wheels are driven, but its axle articulation is pretty good, as is its ground clearance...

what about using tracks, they would use loads of power, but how rough terrain are you looking at going?

Any links to the legal specifications for "mobility buggies" ?
I have a left leg problem which means I can stand but when walking my knee easily dislocates so it limits what I can do.
I don't want a normal buggy but something that I can use for canal towpaths, the moorland only a few hundred yards for me etc.
Limited funds (ie 110% broke) means I've also been thinking of building my own.
I have found details about max speed and lights but that is it - nothing about weight, brakes, or even the min number of wheels.
I'm thinking along the lines, for myself, of a "step though" 2 wheeler with detachable stablisers that their width is easilly & quickly adjustable depending on terrain.

Paul Humphries.

sensible, if you made the 2 wheels wide enough there would be pretty good stability and ground pressure, might help keep weight down too, but wouldnt it make the CoG problem worse tho?

Just found this on a Canadian forum. It's a FourCross, an off road wheel chair for both abled and disabled users. Looks great fun.

If I were building an electric off-road chair - and god know's I've built enough 'fun' electric vehicles, bikes etc - I would combine something like the above with Heinzmann hub motors.


These are what we used in a heavily modified form on the robot:
Click to view attachment

The hub motors are very impressive. The robot had a good lick of speed about it (18mph) but was capable fo climbing 1:1.5 weighing in at 100kg. They are 24v - although I have been known to run them at 36v. At 48v it will spin the wheels pulling away on tarmac and give a top speed of about 45mph. Sadly, if you spin the wheels once too often - it strips the final output gear!

They have a freewheeling sprague clutch built in - so will only drive one way. We removed that on the robot. I'd leave it in for a chair though so you can freewheel down hills - even faster!

I also used one on a folding electric recumbent bike
Click to view attachment Click to view attachment
which was a lot of fun - if a bit frightening!

The best speed controllers come from a company called 4QD in Cambridge. Don't be tempted just to use a big switch. It will break stuff too often - and you'll find yourself lying in the prickly bushes more often than you want!

There are more, high res photos here

Si

There was a programme on bbc or itv last week where a group of disabled youths went to Naple... they had a selection of offroad wheel chairs which looked pretty tricked out. 4 wheeled with discs & articulating front end. The name of the programme fails me at the mo but Im sure its on again this week. WIll check the listing & let you know if i find anything
Adrian

Take a look in this weeks tvtimes, theres a pic of the wheelchairs in there. Think the programmes on tomorrow or day after
Adrian