Building an Inverted Pendulum System The Ups and Downs of Defying Gravity…

Placed a bid on ebay for a DRC encoder that looks like it will replace the broken encoder.  Same size shaft and has the differential signals I need.

Encoders not quite as bad as I originally thought.  I decided if I could remove the circuit board, I could fix the solder beads on the back of the board and reassemble everything safely.  Started by scraping off all the glue around the edge of the circuit boards.  After a little trial and error with the original non-functioning encoder (and shattering the glass disk on it), I figured out how to pop out the circuit board.  Cleaned up the solder on the back of the boards and reassembled everything.  One encoder works fine now – it has good signals and turns smoothly.  The other encoder still doesn’t work.  It turns out that when I popped out the circuit board, I accidentally yanked one of the wires off the LED which is at the bottom of a deep, dark hole with a lens above it.  No way to possibly reattach that wire.  At least now I only need to buy one replacement encoder.

Today was a bad day.  I decided to replace the cables on the encoders today.  Heated up the soldering iron and got to work.  Removed all the wires from the first encoder, then attached the new wires.  After reassembling everything, I noticed it was very difficult to turn the encoder during about half of each revolution.  Since it was the one I tested with the motor, I thought maybe I had bent the shaft due to a misalignment of the gears or something.  Resigned myself to the possibility of needing to purchase a replacement encoder.  Started on the second encoder a little later in the day.  Removed all the old wires, then noticed it was difficult to turn the shaft on this encoder also.  What I hadn’t realized on the first one was that the glass disk for encoder is directly underneath the circuit board.  When the solder was heated up and melted, it formed a large bead on the back of the circuit board which is now rubbing against the encoder disk.  Both encoders are ruined unless I can find a way to fix them.

Wow!  The metal was shipped and arrived the next day.  It came in this long 5 foot heavy cardboard tube.  Both ends of the tube had a wooden disk inserted and stapled heavily.  I couldn’t remove the staples, so I ended up cutting off one of the ends with a hand saw.  Messy, but it worked.  All the metal pieces look pretty good.

Ethernet cable arrived today.  Cut off one end to see what kind of shielding it has.  It looks like it has plenty.  Each pair of wires is wrapped in foil, and the whole thing has a braided wire shield around it.  Should work great as a replacement cable for the encoders.

Ordered several pieces of aluminum from Online Metals.  Ordered one foot pieces of each of the extrusions used to build the cart just in case I need to rebuild it at some point.  Ordered a four foot 1/2” square rod to attach the rack gear to the shelf.  The rack will be bolted to the bar, then the bar will be screwed down to the shelf.  Also ordered a 3 foot 1/2” diameter bar to use as the pendulum.  Even with shipping, the prices were much lower than buying all the metal at the hardware store.

NI has a sbRIO ready and waiting for me.  They just need to test it and then they will ship it to me.  Hurray!!

Today was a big day.  Cut the aluminum pieces for the cart.  We only had 2” aluminum angle, so we carefully cut one leg off to get a 2” wide strip.  It isn’t perfect (kind of ugly) but it worked and I didn’t have to buy another piece of aluminum.  Drilled a bunch of holes with a drill press.  I learned I am not very good at using a drill press.  Most of my holes were not centered, even after using a punch to mark where they were supposed to be.  After a little rework got everything good enough to put it all together.  The cart looks ugly, but it will do the job.  I’m not running a beauty pageant, after all.

Ordered a 15 foot CAT6a ethernet cable through ebay.  That should give me enough cable to make up to three encoder cables, 5 foot each.

The longer cable for the motor came in today.  Used the wiring kit and followed all the directions.  Looks pretty good.  The motor spins nicely when I connect it directly to the 24 V power supply.

Super Droid Robots replied to my email.  They said to just order another motor wiring kit and ask for just four feet of cable instead of all the other stuff.  Placed the order tonight.  It is going to cost about the same to ship the cable as the cable itself.

Stopped by Home Depot and picked up a nice black shelf to mount everything on for $9.  It is 4 ft x 1 ft and just over 1/2” thick.  The cart should be able to travel the entire length of the board, minus a small amount on each end for the shaft supports.  The cart is about 7 inches deep, so that will leave about 5 inches at the back of the shelf for the power supply and sbRIO.  The sbRIO will be a tight fit, but it might be able to squeeze under the slide unit.

Picked up some shim foil that is 1/1000” thick to wrap around the motor shaft and tighten up the gear.  Cut a narrow strip about 1/2” wide and wrapped three times around the shaft.  Gear now fits perfectly with no wobble.

Tested the encoders today.  The two I thought were good worked perfectly with no problems.  The one with the shaft that turns roughly doesn’t have any signal, which doesn’t surprise me.  I guess the guy just threw it in with the others to get rid of it.