Meetup report: 3 May 2018

We had an interesting evening. My phone camera is fuzzy, and I forgot to take lots of photos again...

Otto showed us his 3D printer battery holder for an ancient Festo drill/driver. Great design, with space for 4 18650 cells and a voltmeter to provide manual discharge cutoff. A really solid way to upcycle a rugged tool with modern batteries. No photos, aaargh.

Otto also brought his Fluke scopemeter, and we hooked it up to the pendulum wave op-amp output and the FET gate. There’s a lot of noise, but the signals from the coil picking up the magnet (amplified by the op-amp) comes through nicely. We got a 500mV swing either way of the average.

coil op-amp signals

You can also clearly see the asymmetry in the signal caused by the coil being offset from the center position. The output of the op-amp shows a clear grouping of 2 pulses with a longer pause between them, exactly as planned.

Driving signal, interference and pulse length

We measured the op-amp pulse length, and it’s about 50ms from the start of the rise to the zero-crossing. This corresponds well to my observations that a driving pulse of longer than about 45ms did nothing to drive the pendulum faster.

We picked up no interference from the other pendulums. However, we saw some big spurious signals when the other coils were firing.

Steph and Tom got the Arduino on the Alphabot working, and with some help from a spare lipo battery I had lying around, got the wheels turning. Needs batteries.

I also got the 3D printer printing, but the filament broke inside the extruder, where I could not see it, so I only printed a part once everyone was gone.

Altogether a nice evening. Doing it again this Thursday 6:30 pm.