The sensors I want to use are ‘absolute optical encoders’ and they run about $285 each. For the LIFESUIT robotic exoskeleton to have redundancy I need 44 units. For me redundancy is everything for safety sake. I forces the robot to double check everything. That is sort of an over simplified version of how it works but that is it. Since giving is down and we have now government funding for the last three years I am on my own for the sensors.
Fortunately I am a collector. Most of the time this is bad, because of all the junk I end up saving. I had a new engineering student join the team and come to the lab a couple of years ago. We were in a smaller location, just over a thousand (1000) square feet. He looked at the shelves of stuff I use for prototyping and said when I asked him how he would reorganize it “I would get a twenty foot dumpster and throw it all out”.
LIFESUIT robotic exoskeleton LS14B worn by Monty K Reed with Ben Edes and Doug Bell
It is kind of funny. A few weeks after that our team was working on a new problem for paraplegics who want to transfer from a wheelchair to the bed, the toilet, the bathtub, a car seat or a park bench. Because of the collection of prototype stuff we were able to spend a few minutes looking for parts inside the lab and in a couple of hours we had a working prototype. That device is in testing and could be available to help a paralyzed person to perform the average eighteen (18) transfers a day that most of them perform. It may be covered by insurance too.
My point about being lucky that I am a collector is that, in my collection of parts I have boxes of resistors. Well millions of resistors, if you need some you can have them free. Please send me an email at monty@theyshallwalk.org and let me know what value range you are interested in. If I have it I will send you a hundred (100) or a few thousand (1000+). I digress, my point is that I have pots (potentiometers) that are used to adjust volume on audio equipment. Not the best for thousands of reps but for a robot that needs to walk a few feet a few hundred times it might work. I have 400 of one size that seems to work.
We build a proto board (solder-less breadboard ) and attached it to the ‘brain pak’ of the LIFESUIT robotic exoskeleton. By sensing the feedback through the pot we come up with a number that represents the rotary position of the dial on the pot. Imagine a volume control on you ipod or an older stereo where you turn it counter clockwise all the way and the volume value is zero (0) then you turn it all the way clockwise and the value is 100. If your volume knob turns 300 degrees or so like the ones we have in the box then you can imagine drawing a circle around the knob and marking the degrees of rotation.
We built a table (chart) with the feedback (FB) value of the pot on the left and the angle in degrees (AD) on the right…
LIFESUIT robotic exoskeleton sensors (right and upper) LS15 axle and bearing (lower left)
0 – 0 23 – 15 54 – 30 79 – 45 293 – 180 564 – 360
The scale looks off at first glance, but when you test it over and over the values are consistent. I noticed that each of the pots will give a value range that is close enough to the degrees we want so I was able to modify the software code adjust the movement of the robots legs. For instance in the line of software code I told the actuator to move (extend) until the value of the pot was greater than 77 and less than 81. For that particular joint and that particular sensor the actuator would stop at 45 degrees.
It is amazing that we could save $12,540 on sensors because I am a collector.
We just had the annual fire inspection at the lab. The Seattle Fire Department Firefighters are great. I am impressed with firefighters as a whole because they are very much like soldiers, willing to give it up, give it all up to protect people they do not know. I am glad my stuff is orderly stored and safely accessible.
Lab tour volunteers and visitors
We have a school called “Room Nine” that will be coming to the lab for a field trip this next week. I look forward to speaking to the kids, teachers and parents about science and technology and what we do at They Shall Walk. Next week I will also be visiting the Alderwood Middle School to do an assembly.
The volunteers we have in the lab are the people that make this thing happen, without them I could not do what I do. I want to thank all of the volunteers.
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