Why is Phoebe so manic?

Given that Phoebe and Chloe are so similar, why is their behaviour so different?  Chloe is like a Mum: calm, mellow and thoughtful; Phoebe is like her 3 year old daughter, bouncing around, screaming with delight right to the point she hurts herself and starts crying*.

I’ve been thinking about what could be through cause of this behaviour; the HoG’s are identical, which means hardware.

Motors:

  • Chloe’s has T-motor MN3501-16 12N14P (12 coils, 14 magnets)
  • Phoebe’s has T-motors MT2216-11 12N14P (12 coils, 14 magnets)

Because they have the same coil / magnet configuration, if they have the same ESC with the same PWM pulse width feeding it, they will rotate at the same speed, so this isn’t it.

Props

  • Chloe’s has T-motor 13 x 4.4 CF props – the larger of the two sizes recommended for use with 11.1 batteries and the motors (above) she has
  • Phoebe’s has T-motor 11 x 3.7 CF props – the middle of the 3 sets of props recommended for use with 11.1V batteries, and the motors (above) she has

So assuming they use identical PWM and ESCs and the motors above with identical coil / magnets, how much power to their props generate?  Dunno, but given Chloe weighs more than Phoebe, and has longer arms than Phoebe, there’s some logic that suggests she needs proportionally larger bigger props, which she does.  So this doesn’t seem a likely cause.

ESCs

  • Chloe’s has T-motor 30A opto ESCs
  • Phoebe has DJI 30A opto ESCs

The translation of the PWM pulse to the motors coil switching is very specific to each ESC – the details can only be found from the code running on the microcontroller inside the ESC so I have little to really prove it’s the ESCs fault except DJI have replaced the ESCs I use with new ones – perhaps related to Phoebe’s nutty behaviour – at least that’s plausible.

And last, but not least comes Noise

  • Chloe’s HoG is attached to the rest of her frame with very soft silicone grommets; there is no hard physically connect between her HoG and the motor / prop noise transmitted through the rest of the frame.
  • Phoebe on the other hand is directly connected to the rest of the frame and feels everything.

I already have silicone grommets on order (and they should have arrived today), so I shall be fitting those as soon as they arrive.

I may well also buy new ESCs for Phoebe that match Chloe, but I’ll need to check my bank account first as they’ll be £125 for 4!

Why bother?  Because Phoebe is running through props at probably 10 times the rate Chloe does, and so even a change in ESCs will pay for itself within a month!

P.S. While I was search for what 12N14P meant, I found this article about how to wind the coils of a 12N14P motor – worth a read if only for background knowledge.


*Through experience within earshot right know, the comparison I’ve made between Phoebe and Chloe, and my wife and daughter is absolutely accurate!

Swapping motors, swapping problems

I’ve swapped the standard DJI motors + plastic blades back to the T-Motor + Carbon fiber blades; sure enough, no rocketting up into the sky, and once more I was able to complete a flight.  But…

all the old problems I had returned – excessive drift and yaw.

That suggests

  • the DJI motors are not powerful enough to manage the angular momentum of their heavier plastic blades
  • the T-motors are not all equal  – from the direction of the drift, I would guess the right-hand pair are damaged leading to drift and yaw.

So I have no choice but to buy new motors T-motors, and see what happens.  Hopefully that will sort things out and I can get back to real testing of my control software PIDs rather than diagnosing bizarre behaviour due to dodgy hardware.

So frustrating wasting my very limited testing time on something that turns out to be not my fault!