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

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.

Couldn’t find anywhere to order a longer cable with a shielded single pair of wires heavy enough to power the motor.  Sent an email to Super Droid Robots asking if I could get a longer cable from them.

Also having trouble finding cable for the encoders.  The original cables have four pairs of twisted wires and the whole thing is wrapped in foil.  Found a place online to order cables, but the price was fairly high for the number of feet I need.  Finally found the best solution – it turns out that ethernet cable also has four pairs of twisted wires.  If you get CAT6 ethernet cable, it is shielded.  Now I just have to find some cheap, shielded ethernet cable.

The encoders arrived today.  I was really surprised when there were three encoders in the box and I only paid for two.  One of them turns pretty roughly though, so it may not work.  I will definitely need to replace the cables – the existing cables are about 6 inches long, and I need about 4 feet.

The power supply arrived also.  It is a nice and shiny metal box with terminals on one end.  Looks like it should do the job.

Just got a message that the encoders were shipped today.  I assumed they had been shipped a week or two ago.