Beauty is in the eye of the beholder,

so behold her(mione):



Here’s a quick test flight just to check I’ve not broken anything; more details on Vimeo.

It all started with the props: I’d broken 6 of the CF ones in the last week or two (costing £110 to replace) and on hunting for cheaper alternatives*, I found the white beechwood T-motor props.  They are half the price, stronger, and less likely to split on impact – the CF ones are actually a sandwich with a middle layer of what looks like wood fibre and any lateral contact with the ground and the sandwich splits in three.

The new props’ span is an inch shorter but with slightly higher pitch; after an initial test flight, it was clear they were more powerful as a result. They also look nicer, and that’s what triggered the rest of the makeover.

I’ve been looking for a chapeau to cover her beret PCB for ages (the PCB doesn’t conform to the standard HAT definition, hence beret), and over time I’ve built up a collection of yellow and orange plastic salad bowls as a result, but none quite fitted right.  But with the new white colour scheme, I found one that fitted nigh on perfectly, just a little dremel trimming required.

Finally, the feet: these are rubber lacrosse balls.  They are heavier and stronger than the previous yellow dodgeball foam feet that Hermione forever punched holes through on landing.  The increased prop power more than copes with the extra foot weight.

I think the new look added nearly a kilo in total, and measuring her on the scales, she now weighs 4.6kg, so it’s amazing she takes off at all!

*The problem with most more-affordable props is they don’t fit upside-down on the ground facing motors in Hermione’s X8 format frame.

Vibration damping

So if I can’t get the sampling up to 1kHz to average out vibration, perhaps I can do more to suppress the vibration physically before it gets to the sensors?  Currently just 3mm foam tape sticking the Raspberry Pi to the frame is all there is.  I’ve tinkered with additional vibration suppression in the past but gave up as there were much bigger problems to deal with.

And then just the other day, I stumbled on this site and a cunning plan hatched.

The idea is that the physical strength of the frame lies between the top plate and the top of each arm with 4 bolts per arm.  But the Raspberry Pi and sensor Beret sit on the lower plate with 2 bolts per arm.  If I could put vibration damping between the lower plate and the lower side of each arm, vibrations from the motors could be damped before reaching the Beret / sensors.

Vibration Damping

Vibration Damping

I already have the upper solution using rubber dampers from my previous attempt at vibration damping, but I prefer the lower solution using the silicone gel grommets.

Just one problem: both rely on M3 bolts, but the DJI Flamewheel F450 frame as used by Phoebe uses M2.5 bolts.  ‘Luckily’, the T-motor extension arms as used by Chloe use M3 bolts.

The only downside is that to save cash, I need to splice Phoebe and Chloe together – Chloë’s hardware mind melds with Phoebe’s software and electronics to make a hybrid for which I don’t have a suitable name – any ideas?

P.S. Zoë = Phoebe + Chloë; // my best choice so far.

The Mad Hatter

Made Ahead of Design for HAT Techology Even Released.

As soon as the B+ was released but prior to the HAT specification, I was on the case for a PCB version of a breadboard on which to place the sensors.  I put together some very rough layouts, and Flyfish Technologies kindly converted a crude design into a much cleaner layout with a production run of ten at a very reasonable price.

Chlöe - The Mad Hatter

Chlöe – The Mad Hatter

To be clear, this is not a HAT – it lacks the spacing for the Camera (CSI) and Display (DSI) cable spaces, along with self-identification / configuration EEPROM.  But it’s perfect for Phoebe’s big sister Chlöe.  More on her in another blog when some parts arrive in a couple of weeks.  Until then, I’ll probably run Phoebe a few more time, perhaps with better calibration, but she has served her purpose well and is heading towards retirement.

P.S. Eagle layout file is now on GitHub – beret.brd.