A blast from the past

For the last few days, the outdoor temperature dropped to the teens from the twenties.  As a result, she didn’t get off the ground; she just jittered around.  The graph of double integrated (accelerometer – gravity) shows she believed she’s was climbing right at the point the IMU temperature dropped.

Not again :-(

Not again 🙁

This looks awfully similar to this.

The problem is that in these cooler temperatures, once the props start spinning, the IMU cools, and the temperature sensitive accelerometer output shifts as a result.  Because I take a snapshot of gravity prior to the props spinning, net acceleration (accelerometer – gravity) is wrong, so integrating it twice to get distances is very very wrong.

The problem showed up this time because to add the salad bowl lid,  I had to remove her Pimoroni Tangerine Dream PiBow, thus exposing her to the elements. For now, I’ve just moved the initial read of gravity to immediately before take off, but I’m also working out how to reintroduce the PiBox case or similar in a lower profile version to that the salad bowl still fits neatly on top.

Tangerine dream

I’m waiting for a new PCB for Hermione which hopefully will sort out the I²C errors that the Garmin seems to be the source of.  That means I have 10 days to kill with nearly nothing to do except this – putting her HoG in a Pimoroni Tangerine PiBow:

Tangerine PiBow

Tangerine PiBow

The part that pleases me most is actually the RaspiCam cabling that can be folded flat, nicely fitting between the RPi and the PCB, and emerging from the case dead-center above the video connector.

Once complete and with the new PCB installed, the case can be extended to have a lid (the current PCB overruns the case by the GPIO pins), providing crash and weather protection for Hermione’s HoG* (or should that be Hermione’s HoT now?).

I’ve countersunk the M3 underside corner-holes of case level 0 so the base is flat, allowing the case to be attached to the frame with a double sided foam pad.  To ensure the RPi is held firmly within the case, it’s bolted to the underside of layer 3 with 8mm M2.5 standoffs on the top of layer 3 to connect to the PCB.  This does raise the RPi slightly higher (it’s intended to sit loosely on layer 2) and so some careful filing is needed on the underside of layer 5, both for the camera cable and the HDMI connector.  But as you can see, the result is a perfect fit.  The new PCB (also in Tangerine from Ragworm) will fit perfectly inside.

I just hope the new PCB does resolve the I²C problem so that this make-up doesn’t prove to be Hermione’s end-of-the-line.


*HoG (Heart of Gold) is the the ship from Douglas Adams’ “Hitchhikers’ Guide to the Galaxy” which contains the Infinite Improbability Drive which allowed faster-than-light travel when provided with the Brownian motion source; I consume 3 pints of tea each morning to meet her needs.

Cotswold Jam tutorial kits vs. Dyson

I’ve just quit smoking saving myself £300 a month, and I was going to treat myself to a new vacuum cleaner as a reward – I have an older version of the same and it’s fab but this one is even fabber.

But I’ve also started putting together a new python + electronics tutorial for the next Cotswold Jam at the end of April, both setting up my own prototype, and collecting components for 24 kits to be given away to tutorial participants.  Sadly, this has taken a significant proportion of my Dyson money, but I think the result of my prototype looks pretty cool, literally:

Door alarm system

Door alarm system

Big thanks to Pimoroni for the custom Snowflake white version of their limited edition PiBow B+/B2 Coupe Midnight Black, the discount on the 25 mini-PCBs for the kits – you’re stars!

The give away kits will have smaller breadboards instead of the cakeboard shown above, but they’ll all come with the doors with neodymium magnets as the door knobs, reed switch, buzzer, on-off switch and wires.