Just built a large/heavy X8 config running 3.3.3 - 12 pounds and 17.5" props. Tiger 80A ESC and KDE 360 kV motors.
On the initial flight test the X8 would yaw left without input and even at full yaw input would barely rotate to the right. The log files show a pretty large difference in mean output between the CCW motors (outputs 1,3,5,7) and the CW motors (outputs 2,4,6,8) (see attached). I can't find conclusive information on this, but logically it seems like this should not be occurring. I'd expect all 8 motors to have output levels about the same when at a steady hover, is this accurate?
If so, what could be causing this? Obviously I've checked and rechecked the motor connections, spin direction and prop direction.
Replies
Thank you for backing me up Leonard, and thank you for being a dev.
Based on my experience, brushless motors/ESCs vary about 5-10% in output vs. PWM signal. They simply are not all equal. Sorry to say but if you give two off the shelf ESC/motor sets exactly the same voltage and PWM signal, they will spin 5-10% different RPM.
@Jimmy,
are you in position to verify your opinion by live motor test data ?
What you say could ground all DIY drones built from parts purchased remotely,
under new legislation on personal drone airworthiness pending in Senate.
"
if you give two off the shelf ESC/motor sets exactly the same voltage and PWM signal, they will spin 5-10% different RPM.
"
Does it mean, in case of 2 badly matched motors they will spin 10-20% different RPM , resulting in 20% thrust/lift difference or 20 ** 2 = 40% thrust / lift force difference ?
Does it mean we should ask manufacturers of motors to preselect 4- 6- 8- piece motor sets for those assembling personal drones ?
Darius, I do not have an opinion on the matter. As I said above, from my experience this is what I've observed.
Your posts make it sound like you have not done these tests yourself, however.
@Jimmy Underhill,
you claimed feature making not preselected motor not fit to build personal drone.
Could you name manufacturer, type, model, manufacture year of motors tested by you to let me verify you claims directly with a manufacturer ?
If what you claim is for true and can be verified by independent aircraft labs, all developers of personal drone risk violating of personal drone (aircraft under latest regulation by FAA) airthworthiness and grounding of such home built personal drone aircraft for the cause mentioned by you.
I always buy certified electronic products, motors coming with technical specification, performance charts by default.
Why didn't you report problems with motors earlier at DOYDrones ?
Is FAA aware of the problem ?
Having a hard time understanding your grammar, sorry. I've tested motors from Sunnysky, Team Blacksheep, T-Motor, KDE, and DJI and this is my experience.
As was said earlier, it's not a problem, simply reality.
No problems with your semantics.
Do motors in Solo and other models by 3DR feature the same syndrome ?
Did you do labs-grade motor stand tests and can share performance charts, RPM vs. PWM input for tested motors by make, model, type, power, manufacture date on the file ?
Because it is not a problem. You would know this if you had ever flown one.
Also you are dead wrong when you say risk violation of regulation by FAA. You are talking about hypothetical rules which are still under review. Anyway, show me the line where it says motors must follow a thrust curve. I doubt it exists.
Same experience here, on several X8s of various sizes, from 15" to 28" prop size.
Darius it does not matter because the autopilot does not assume that motor response is identical. You can fly with sand in the bearings, chipped props, uneven weight distribution, and in the case of octocopters/X8s: entirely missing or upsidedown props. (But obviously these are not good practices.) You can do this because the autopilot compensates, take a class on control theory.
Stop fear mongering about the FAA reauthorization. IF a piece of legislation comes out which affects the DIY market, we'll cross that bridge when we come to it.
-
1
-
2
-
3
-
4
-
5
of 5 Next