Sunday, 23 March 2014

Jammin' at UCP

Saturday, 15 March  Raspberry Jam - University Centre Peterborough (UCP)

UCP is a small, modern university campus of Peterborough Regional College, and venue for the very first Raspberry Jam to be held in Peterborough organized by Mike Mills.

Arriving early to setup the Armdroid in the Show & Tell display section:

The tea-tray was borrowed because in the afternoon I was to give a short presentation and needed a way of carrying everything upstairs to the conference room.

All reduction gears lucubrated with oil, and my original 12V power supply was chosen in favor of the 15V supply to put less stress on the motors, as these will be mostly powered all day.   I don't yet have any control in my Arduino firmware to enable/disable Holding Torque which would have allowed me to cool down the stepper motors by de-energizing the coils during long periods of standby.

Whilst the opening presentations were being held, the show & tell area was quite, so I had time to experiment further with different speed settings.  The Armdroid performs really well at 200RPM, but excessive vibrations seem to occur at speeds lower than 100RPM.  This is especially notable with base rotations, and additional lubrication applied to the bearings didn't seem to help matters.

I eventually pushed the speed right up to approx 600RPM and at this point, things started to go unpredictably wrong, so 500RPM would appear to be the safest maximum top-speed.   Switching off, and re-positioning the arm back to a predefined home position recovered everything nicely.

Unfortunately I didn't have time to write any sequencing software before the show, so all movements had to be instructed by commands entered manually on the Raspberry Pi.

The show & tell became very busy, and in the afternoon gave a 30-min presentation to an over-subscribed class room, and despite having not preparing any material, went surprisingly well.   It was pleasing to hear from people who previously saw the Armdroid at Cambridge saying how much smoother everything is running these days.

I would like to congratulate Mike and all helpers for putting on a great show.  It was also fantastic to catch up with familiar faces from previous Milton Keynes (Bletchley Park) and Cambridge Jams.

As before, I've come away with a list of things/issues to address:

  • Gripper - the precision of fingers closing is not as accurate as I would like and makes picking up objects unreliable
  • Sequencing software for the Raspberry Pi
  • Pre-designed sequences to really demonstrate & show off capabilities
  • Motion limiters - add protection from operating outside working envelope
  • Sensors - must install original reed-switches and update the Arduino to accept the bi-directional interface on the digital I/O pins
  • Torque control
  • Investigate use of PIGPIO for low-level driving from the Pi instead of slaving out to an Arduino

As hinted in my presentation I'll also be looking to design "applications" which will use the robotic arm to solve some real-world problems, so hopefully, in time we'll have something really interesting and impressive to show....

Photographs used with permission - John Evans

Additional photographs :

I'll add more links / pictures from the show when I find them....