golf cart steering

[Tom Line]

I can think of a couple ways to do this.

Foot steering could be accomplished by using a turntable (torsion spring return to center) that you put your foot and twist to turn, and having an absolute encoder or potentiometer give the feedback to a control system that controls the electric motor.

The actual steering could be accomplished through an electric rack and pinion setup - you may be able to get one cheap off the net for existing cars.

Or, conversely, you could make your own rack and pinion setup.

Or, you could run a small motor in a transmission to a winch with wires running to the end of each A-arm. This is probably the simplest as you wouldn't have to worry about any type of mechanical alignment with the steering system and a rack.

I'd also look at RC cars. They use a servo with a few simple lever-linkages for steering. You could do the same here, and use an electric motor with feedback through a small transmission as a pseudo-servo.

Finally and probably the most simple would be directly turning the steering column with a motor through a small transmission. You could use a lever and a super-shifter transmission so that even has a neutral gear so that you could hand steer it!

To tell you the truth - this is all something that many of the First Robotics team here could pull off with their machining facilities. Maybe you could even hit up someone for one of the old IFI control systems to program it all for you.

Edit - it looks like Don and I had a lot of the same ideas, but I just thought of another one. Instead of a turntable, use a lever that turns, similar to the way the hand on a clock turns. Put a shoe-catch like they have on long-distance bikes that the toe of your shoe goes in. Then he rocks his ankle left to go left and right to go right. This would be easier than a turntable though it would work on the same philosopy. It would be pretty easy to make.

[EricVanWyk]

I think the most important part will be the user interface, not the implementation. Take the time to figure out what is most comfortable before moving forward. Assume that anything is possible (at(in?) first).

Originally Posted by Tom Line

Foot steering could be accomplished by using a turntable (torsion spring return to center) that you put your foot and twist to turn, and having an absolute encoder or potentiometer give the feedback to a control system that controls the electric motor.

I've seen this done "in real life". One of our patients who had had both arms amputated drove his car this way. One foot for gas / brakes. One foot for steering with a turn table. Not sure what the linkage was.

[PAR_WIG1350]

http://www.velovision.co.uk/mag/issu...alneeds150.pdf

This is actually from a cycling magazine, but page six mentions hands-free steering and provides a web address. A similar interface could be used even if you keep the same steering mechanism, it could potentially be interfaced into the existing steering column with control cables.

[DonRotolo]

Originally Posted by Tom Line

Foot steering could be accomplished by using a turntable (torsion spring return to center) that you put your foot and twist to turn

Originally Posted by EricVanWyk

I think the most important part will be the user interface, not the implementation.

Two important points.

With the turntable idea: Imagine if the steering wheel was on the floor. Wouldn't that be pretty good? Maybe that can be done with a sawzall or something relatively simple like that.

But Eric's point is critical: What is best for the user? We need to hear more about that before we go much further.

[The Analog]

how about 2 gas pedals, one for the left wheels, and one for the right, then you have a tank drive, it might require some major changes to the golf carts drive train

[EricH]

Originally Posted by The Analog

how about 2 gas pedals, one for the left wheels, and one for the right, then you have a tank drive, it might require some major changes to the golf carts drive train

Take away the "might" in that. Is it doable? Yes, but not easily. (Golf carts use steering like cars; modding that would need a second motor and locking the front wheels at minimum, let alone control setup.)

Depending on the user's ability, and on the golf cart's steering column/body surrounding the steering column, I would actually go with putting a second steering wheel onto that rod at foot level, if at all possible. It's simple, it doesn't affect usability if he wants to be driven instead of do the driving, and it may actually be pretty cheap.

[Gdeaver]

First, Does your son have no hand function at all? My father had a progressive brain disease that left his body frozen. We got him an electric wheel chair the hover 'round. Its joy stick interface is extremely well implemented and could be used if there is any hand function at all. Well engineered product. I have also seen wheel chair control for people with no body function implemented with a bulb for velocity. The harder you bite, the faster you go. Turning was controlled by head movement. You look at where you want to go. There are many commercial solutions on the market that would be safer and a whole lot easier than a golf cart kludge. However, even with insurance you will have to lay out some substantial money.

[MrForbes]

Tiller grasped between the knees? would leave feet free for accelerator/brake, might be more natural to drive?

I'd spend more time seeing what's already available, most (but definitely not all) of the good ideas have been thought of....

[ajd]

Originally Posted by EricH

Take away the "might" in that. Is it doable? Yes, but not easily. (Golf carts use steering like cars; modding that would need a second motor and locking the front wheels at minimum, let alone control setup.)

You could still use rack-and-pinion steering with such a scheme; the input would just be tank drive. You would have to come up with a mechanical way to convert between the two representations, though, unless you consider drive-by-wire solutions.

[biojae]

Originally Posted by ajd

You could still use rack-and-pinion steering with such a scheme; the input would just be tank drive. You would have to come up with a mechanical way to convert between the two representations, though, unless you consider drive-by-wire solutions.

Converting the tank drive commands to velocity and steering would not be too hard.

Velocity = (L + R) / 2
Turn      =  (L - R) / 2

Though, the cart won't react the same way as a First robot.
Mainly because the cart can't turn in place, only in arcs.

I would keep the steering control type as close to the original as possible (ie a turn-table would be fine because it is still a type of rotary interface that has a one-to-one relation with the cart's steering, like the original steering wheel)

[EricH]

Originally Posted by ajd

You could still use rack-and-pinion steering with such a scheme; the input would just be tank drive. You would have to come up with a mechanical way to convert between the two representations, though, unless you consider drive-by-wire solutions.

If it's a RWD, add a motor. If it's 4WD or front-wheel drive, it's a lot harder.

It's simpler if you can just add a second steering wheel near foot level.

[PAR_WIG1350]

what about an arm or arms directly attached or geared to the steering wheel that allow it to be controlled by moving one's knee from side to side.
a Y shaped bar that straddles one's knee is both cheap and effective gearing could be used to amplify inputs, since a direct connection wouldn't be very agile without having to lift your knee, and then you wouldn't be able to operate the pedals.

[jspatz1]

I fully agree that the right input method is more critical than the mechanical actuation method. A turntable/floor wheel under the left foot feels like the right input solution to me. Fairly natural, easy to get on and off of, no strange input devices in the way elsewhere. Could even leave the normal steering wheel in place so it is still usable by anyone. The lower leg is pretty strong compared to hands and wrists, and should be able to duplicate the effort required for normal steering. The golf carts I've used steer very easily, so perhaps this could be tied directly into the existing linkage. If he has full strength in his legs then it really seems like there is enough strength in the leg to steer without an actuator or assist. But if some actuator or power assist is needed, why not borrow the power steering method for cars that is already highly developed and readily available? I'll bet a good mechanic or car hobbyist could select and adapt the power steering components from a salvage yard that would do the trick. Sounds like an interesting project, wish I had time for it myself.