Originally Posted by Don Rotolo (Post 966307)

OK, so do we find you a team in Orlando, a team in Va Beach, or both?

Also, before we start: We are a bunch of practical guys, some engineers, some not, and a LOT of High School kids, here on this forum. You and your son need to be the final deciders if something is safe or not.

OK, let's understand the problem: He has some use of his legs, but not his arms or hands. That means to me that he can use throttle and brake, but not steer. Is that right? yes, correct

Going on that assumption, if the right foot is go/stop, the left foot needs to be steering.

Problem #1: How does the left foot control steering. That is, does one use a gas pedal type control (press for right, pull for left) or a side-to-side lever? I would hesitate for a push/pull arrangement, since a big bump could cause an inadvertent turn. But, think about your son's capabilities and let us know what you think. he is capable of most anything

Problem #2: OK, we have some kind of input, how to we physically move the steering wheel?

A linear actuator directly on the steering box sounds nice, but as you said most are really not suited for that - but check McMaster.com and Google for other styles that might be workable.

Pneumatics are right out, since they can't hold a given position (Air compresses)

Hydraulics are fine, but need a pump for pressure and some plumbing. You don't need a lot of power (= thin cylinder, maybe 1" or so), but the controlling is pure mechanical.

Any of the above require a permanent modification of the cart, and people without a special skill can't drive it easily.

Another idea is to install a sprocket onto the steering wheel, and use a motor to turn it via chain drive. Make a method of de-energizing the motor and anyone can steer it. Electronic controls are light and cheap. I like this idea the most so far. this was my first idea but i think it would have to be a geared head motor

For a motor, look for a large servo motor. A servo motor is a special motor that provides feedback for its exact position. Using some basic electronics you can command it to, say, 7.2 degrees right and it'll go and stay there. The controls can take several forms, so as he improves different control schemes can be considered, not just a lever at his left foot.

Thinking off topic a little, he might even be able to control this with his head - turn right to steer right, and so on. Does he have good control of his neck?

OK, enough speculating for now. Let us know about #1.
Oh yes, we also need to know a little about you: Your experience, skills, machining capabilities, and budget.

Originally Posted by Don Rotolo (Post 966884)

I agree, if there's a way to get him some aerobic exercise in the deal, it's good. But we don't want to tire him out just yet.

Instead of complex electric motors, sensors and and chains and stuff, maybe just a linkage between a foot plate for steering and the original steering shaft. Left foot steers, right foot gas/brake. Simple is usually best.

Let us know how we can help.

Originally Posted by theaznevan (Post 967398)

wow everyone here has got great ideas, and i take no offense if you guys don't like my idea. how about a tank drive kind of system, two pedals, one on the left other on the right and each control its respectable side of the cart. (right controls right side wheels, vice versa). another parking brake kind of pedal can control forward/reverse drive. the problem i see here is this system is highly custom configuration and might cost big bucks. nevertheless its an idea! not very detail im afraid though haha. i wish the best of luck and recovery to you, your son and your family!

Originally Posted by EricH (Post 967397)

The problem you'd get with a second wheel is the lock-to-lock turning is 3 full turns. Most of the time, you'd only need a little bit of steering, but when making a tight turn, you can easily run into trouble. If that were done, I'd locate it off the drive shaft (structural addition may be needed) and link it 1:1 or maybe 1:1.5, then put a spinning flat knob on the additional wheel, equipped with a bicycle toe clip and most probably a heel jam of some form, to allow the driver to fully turn the wheel. Some buses have a small knob sticking up from the wheel; this would serve a similar function.