Disabled man needs help with electric steering 'pics'

[brokin]

Hello,
My name is Dwayne, I'm a quadreplegic due to a diving accident that broke my neck in 1994. i am totally paralyized from my armpits down and i hve lost the use of my grip in my hands and the triceps in my arms making my arms weak and unable to steer a straight rack steering vehicle.
I have been searching for a vehicle i could easily adapt to my disability so i could drive it. I bought a carter dlx off road kart that was easily modified to hand controls for gas and brake, it has rack and pinion steering but it is so stiff i cant turn the wheel.
We tried electric cylinders/rams and they were to slow, we also tried using a 24vdc motor coupled to the rack its self, it was inconsistent and unpredictable, hydraulics wont work as it has no PTO for a pump and the electric hydraulic pumps use lots of power and would sap my batteries plus I'm told they wouldn't be able to run constant anyway [ less than 30 mins constant run time ]. I'd like to convert it to electric power steering i know from research the Honda insight, Honda s2000 and the Honda nsx uses an electric power steering rack but i cant find one anywhere so i don't know if we could make one work or not .

So heres where i am, i have the buggy with hand controls working great but cant steer it. I have as of now 2 deep cycle 12vdc batteries mounted in the passenger floorboard, wired to a momentary dpdt switch to power a dc motor that is coupled directly to the steering rack . Ive tried 12volts and 24 volts to power the steering but neither are perfect and i either get over steer [ 24v ] or under steer [with 12v] and never the exact direction i want to steer in. as speed [ mph ]changes neither of the voltages work well.it either steers to fast when I'm going slow or to slow when I'm going fast.

any ideas how to get electric steering to work or what parts i would need? heres some pics we took before modifying anything....

http://img212.exs.cx/img212/5467/overall5ji.jpg

http://img212.exs.cx/img212/9515/driverfrombehindfullleft9ex.jpg

http://img212.exs.cx/img212/7100/driverfrombehindfullright8bg.jpg

http://img212.exs.cx/img212/5626/driverfrombehindstright1az.jpg

http://img212.exs.cx/img212/1324/010102076aa.jpg

http://img212.exs.cx/img212/7939/010102055ko.jpg

I'd like to get this thing where i could drive it, any ideas are appreciated, we've tried all we can think of..... if you need any more pictures of the buggy's steering setup or measurements just ask and i will provide it, BTW it takes between 35 and 40 ft lbs [ with torque wrench on steering wheel ] to turn the steering wheel.

ive not drove anything in close to 11 years and dont trust myself on the highway so i wanted an offroad cart to ride with the atv'ers in my community, ive had the cart for over a year and still cant figure anything out. any help would be appriciated.

 

[JayMaechtlen]

Hi, Dwayne.
It sounds like the 24V motor supplied with 24V is fast enough, but not controllable?
Sounds like you need a variable-speed drive for the motor.
Find a standard PWM drive (pulse-width modulated) to feed the motor, and drive with input from a joystick or such.
I don't know about the automotive electric P/S, but-
1. keep web-searching
2. Do you have any car dealers in your area? Do they have cars with electric P/S on the lot? Get them to put one up on a rack for examination!
Maybe the parts dept has one on the shelf, or could get one for inspection? Lots of folks have a soft spot for someone in your position.
HTH
regards
Jay

Jay Maechtlen

http://home.covad.net/~jmaechtlen/

 

[Radabaugh]

Hi Dwayne,

First question is what kind of interface do you want to have with the steering. Typical power steering systems (electric or hydraulic) provide assist based on steering wheel torque, so the more torque you apply to the wheel, the more assist they provide. In effect, you supply position control of the steering wheel (and thereby front road wheels) and the assist system provides assist as necessary to minimize the amount of torque required on the steering wheel.

However, if it would be easier for you to do something like a joystick control without force feedback, then you are really looking at doing a position control system where the assist moves the front wheels to whatever location the joystick indicates.

If you would prefer a typical steering setup (option 1 above), then I would look at purchasing a column EPAS setup from a Saturn ION or VUE. Column systems are much more available overseas and can be found on almost all the B-class (think Geo Metro size) cars in Europe or Japan anymore. Go for the oldest ones you can find as they will be simpler, most of the new systems on the market will expect network messages from the car and may not function if they aren't there (assuming your buggy doesn't have a CAN network).

If you can score a Column EPAS unit and a wiring diagram (to get the controller pinouts for things like ignition), then its just a matter of physically mounting it and hooking it up. My guess is that you won't see efforts higher than 1 or 2 Nm on the steering wheel just because the Column EPAS sized for a car will barely be working to steer your buggy.

If you wish to continue with the setup you have, then you basically need to do current control (using PWM) to the motor that is proportional to the steering wheel torque. This would require a torque sensor and a control module capable of doing current control. If you purchase the Column EPAS unit, you get all of that.

If you want to do option 2 above, then it gets a little more difficult. There are a number of offroad hydraulic systems out there that effectively do this, but you said you didn't have hydraulics. To do it electrically, you would need a controller that looks at the joystick position, the rack position, and then applies current when it sees a difference. Doable, but getting more complicated.

Hope this helps.

Scott R.