Phoebe vs. Chloe

So Chloe is working nigh on perfectly – each flight is as good or better than the recent video.

With the same code other than personal 0g tuning and PID gains, Phoebe is still a danger to herself and all around her.

The only real difference in hardware are the silicone grommets separating Chloe’s HoG from Chloe’s main frame noise.

I’d really like to get Phoebe up to Chloe’s standard, as she’s small and therefore easier to transport. Trouble is those grommet seem to be rare as hens teeth. The first source were out of stock, a US seller sent 3 instead of the 10 I ordered, but I do now have a UK supplier so I’ll have another go on Phoebe.

Prototyping Zoë

Zoë is the child of Phoebe and Chloë, taking the best of both and adding a little bit of magic to the mix.  She’s only in a partial build state currently – there’s no point in completing the build until I’m extremely confident in Phoebe’s flights.

At first glance, the finished Zoë will pretty much like Chloë:

Chloë

Chloë

The difference is in the details – and specifically the base plate(s).  Phoebe and Chloë only have a single base; Zoë has two:

Silicone Sandwich

Silicone Sandwich

The lower (base) plate handles power distribution from the LiPo on top out to the ESCs on the arms.  The new intermediate plate lies just a few millimeters above, and carries just the Raspberry Pi flight controller.  This intermediate plate ‘hovers’ above the base plate on a set of silicone grommets.  These are extremely soft, hopefully providing extreme isolation from the power frame’s vibrations, thus allowing the sensors to pick up only real acceleration.  Other than the ESC cables and the micro-USB cable, there is no hard connection between the intermediate plate and the rest of Zoë.

The only slight concern I have is the placement of Zoë’s battery bank.  It can’t sit on the intermediate plate next to the Raspberry Pi as with Phoebe; its too heavy and will squish the dampers on that side.

Power bank placement

Power bank placement

The picture shows it under the bottom plate, but as the arms don’t have hands (see Chloë’s photo at the top), the battery bank would be what hits the floor on landing, and experience tells me it won’t survive many landings that way unless I’m careful!  On the plus side, the way I’ve oriented the bank, the USB B sockets is closest to the base plate given some protection from the USB B plug wrenching the socket off the PSB inside the bank.  I think it’s worth trying as any other solution seems very ugly in comparison.

Last but not least, here’s the top side view; currently, that’s Chloë’s flight controller; Zoë will have her own as there are changes I’d like to make to Phoebe’s controller too.  The nuts and washers attached to the silicone are where Zoë’s arms will connect; they have a rock-solid connection to the base plate right through the centre of the silicone grommets maintaining structural solidity, while the intermediate plate (top in the picture) chills out in her vibration free environment.

Top-side

Top-side

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.