Advice needed on 'neat' Project!

Hey everyone!

a little mechatronics 202 homework problem I made up for myself as I begin to get into haptics and haptic research (See Wikipedia). I am currently figuring out a hardware approach to breadboard before considering the software.. I intend to do motor control with PicBasic, hence my posting here. Thanks for any advice in advance!

Anyhow. Attached and linked is a 'worksheet' I have made to help me figure out how to tackle this rudimentary 1-axis force feedback interactive machine.

Essentially I wanted to make a tug of war machine, but after some tinkering with gears, belts, and motors, I decided to just go super simple, and do a 'Stick'. Incidentally, this is why I have been mooning around about USB lately..

If any of you geniuses out there have any advice about ways to attack this, let me know.. I have considered resistive pressure sensors or similar as well.. But I do not know.. I also considered various scenarios with springs and linear encoders.
<img src="www.robertguyser.com/1axishaptic.gif">

Howw much force are we talking about? 0 to 1 kilo, 0 to 10 k, to 100k, to 100k?
And how big of a machine ? Those parameters and the cost will dictate the methods.

well 'force' is variable.. i would predict some fraction of the average force a human can exert on a rod fixed in all but one direction of movement... I would guess, for conversation, around 100 pounds... 45 kilos...


really i am looking for some insight others might have through their own experience... the hard part as i look at it theoreticaly is allowing a person to manipulate the rod and then have the rod hold the new position..

if 2 people are acting on the rod, i think it becomes more of a closed loop thing..

i am building an h-bridge with current limiting.. i have a theory closed loop positioning, combined with current sensing and dynamic limiting will be the ticket...

really this is a 1-axis haptic device i am trying to 'breadboard'...

any ideas where to look for help? ive posted this on the 3 tech\engineering forums I use with little response...

thanks for the interest joe!

(more illustrations forthcomming!)

Ok the reason I asked you the questions was to get a scale of the project at hand. The cheapest power you can use is likely to be air or hydraulic cylinders. You can power them with an air compressor or a hydraulic pump. I do not suggest straight air power unless an hydraulic secondary cylinder is used to dampen the air cylinders operation as air cylinders tend to move rapidly and all at once. Air over oil will work as well if an orfice is placed inline to restrict flow.
Now as to sensors, a really cheap and available analog sensor is to use the oil pressure sensor from a car that uses an electric gauge, it is simply a pressure variable resistor, it would work in an A/D or POT circuit.

this thing is a bit of a test\research exercise. i am not going to build a full size device right away of this.. more like a 1/5th scale model.. ive worked a bit more at it.. trying to develop pseudo code for each of 4 states ive identified...

currently i am assuming the hardware will be:

DC motor with encoder
linear encoder
pneumatic damper or spring
a reel, some rope, a 18f4550 with usb setup
check this out:

www.robertguyser.com/tugofwar.gif

hELLO,
HSC Electronic Supply's ad in Feb 2007 Nuts N Volts has a 0 to 30 psi pressure transducer for $9.95 p/n hsc #21066 they also have some gear motors