Prototyping on a student budget is always challenging, especially when it comes to prototyping pneumatic robotics and wanting to implement linear motion feedback. To overcome the high costs of industrial linear displacement transducers I decided to build them myself and use them in a working principle prototype. The linear displacement transducers as shown in this instructable are low cost, flexible and versatile however they do not function according any standards.
Step 1: Materials
1) A potentiometer of your choosing
2) A badge reel of your choosing
3) A "servo mounting thingy"
4) A piece of aluminum square tubing of your choosing
5) A small screw
Additional stuff: Glue, Drill, Drilling machine, metal saw, (the nut comes with the potentiometer)
Step 2: Construction
1) Drill the appropriate holes in the aluminum tubing.
2) Take apart the badge reel and keep the reel and the spring.
3) Glue the "servo mounting thingy" to the reel.
4) Place the reel in the aluminum tubing and attach the small screw to the spring.
5) Put the potentiometer to the hole in the aluminum tubing and screw on the nut loosely.
6) Press the head of the potentiometer in the "servo mounting thingy" (it should make a tight fitting such that the potentiometer turns when you pull the string on the reel)
Lastly) Fasten the nut on the potentiometer and voila: A low cost string-pot displacement transducer.
Step 3: Voila
I used the above mentioned string-pot displacement transducer as position feedback in a servo pneumatic robotics working principle prototype and they did the job perfectly. In my next instructable I will show you how to build your own low cost servo valves (up to 8 bar) for servo pneumatic prototyping purposes.