The new PCB arrived, and I’ve done a few indoor tests, and I’ve only seen one I²C error over a total of 60s testing. Previously, the I²C problem would occur in a fraction of a second. So my power spike / noise speculation was probably right but needs refining. Next step is to take Hermione out to build up confidence and to check what video frame resolution she can handle – currently it’s 640 x 640 pixels. Annoyingly there are gales blowing and forecast to stay for the next few days.
I’ve already been designing the layout for the next PCB revision before this one arrived. The main change is that the PCB is fed 5V independently from the Raspberry Pi. Obviously their grounds are connected. The power comes from a dual port (2.5A each) LiPo Battery Bank – one of these already powers my piPad B3 and RPi touch screen independently and beautifully.
In addition, but unrelated to the PCB power solution, the new PCB design includes a button and LED. These are for use in the next phase: setting up a series of points in the flight plan based upon GPS targets.
Essentially, prior to a flight, Hermione is set down in several places, and the button pressed; the LED flashes while a sufficient number of GPS satellites have been acquired, at which point the LED goes on for 1 second, the GPS position is saved to file and the LED goes off. This can be repeated several times to construct a list of GPS positions saved to file as the flight plan.
At the start of a flight, the LED flash / on / off sequence is repeated to acquires enough satellites and record the take-off GPS position; Hermione then climbs to 1m height, and hovers there for a second, yawing to face the first GPS target point saved previously in the flight plan file. Then she heads there at 1m/s. Once at the first GPS point, she hovers again, yawing to point towards the second GPS target, and off she goes again, with the sequence repeated for all of the prerecorded GPS targets. On reaching the final pre-recorded GPS point, once more she hovers for a second while she yaws to face the takeoff GPS point taken at the start of the flight, and back home she goes. Simples!
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:
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.
I simply couldn’t give up on Phoebe so easily: after posting, I spotted all the components needed to build a clean Zoe PCB which I did. I attached it to Phoebe, and everything worked. So the I2C problems are the fault of the breadboard-like PCB Phoebe uses. So once more, Phoebe isn’t dead yet, and the new PCB layout is already in progress for the lovely peeps at Ragworm to produce in the next week or so.
Despite the bitter temperature, Zoë’s been out lots over the past few days to see what the new temperature control was like regarding vertical climb during hover. She takes just over a minute to warm the sensors up to 40ºC and for the sensors to stabilize regardless of ambient temperature. And for the first time since I swapped to motion control processing rather than angular control, she just hovered – she didn’t drift up or down during the hover phase:
Zoë in the snow from Andy Baker on Vimeo.
The ‘fix’ to the problems I’d been seeing due to wind chill was solved by a lump of blue-tak covering the MPU6050 to help keep it warm. Well, that along with a complete rewrite of the start up code that waits for temperature and sensor stabilizationbefore anything else happens. The transformation is amazing!
I’ve also recalibrated the sensors to be confident as she’d been showing a consistent slight drift to starboard. Clearly that’s still there but much better, though also clearly, I need to work on the landings / shutdown to make sure the ESCs have shutdown completelly before the PWM signal to them is turned off!
You might have spotted the golden foam dome has reappeared on her underside to protect the battery and keep it warm. I’m not sure I’ve ever mentioned what the landing dome is: it’s a Slazenger Shortex foam tennis ball sliced up with an electric carving knife normally used for the Sunday joint!
I did run a few more flights after this one, but one of the blades had fractured, so they were a lot less good. As always, it was a right hand blade that got broken, so no more flights until the new ones arrive, probably tomorrow.
Here’s the blade graveyard, just to give you an idea of how many I’ve got through in the last week or so. These are only the ones where the blade was ripped completely off the prop. Ones where the prop still has two blades, but with one damaged go into the bin indoors. Each prop is £15. Ouch!