Will motor failure cause serious yaw?


#1

Hi everyone, I’m very excited about this project!

I am interested to know how much twisting/yaw will result from the failure of a motor.

I saw someone say it will be a big problem. In this case, software would be needed to redistribute power: more power to the motor on the same side as the failed motor, and less to those on the other side.

But someone else said that an in-flight failure of a motor it’s not a problem, and it’s only a problem on takeoff when it might make you swerve as you run!

Just curious about this!

Richard


#2

That’s something I thought would be a bigger issue when we started this project but it turns out is not that much of a risk. We are still developing software to redistribute power just to be extra safe, you can always just throttle down if a motor goes out (which is very very unlikely). As the motors don’t stop instantly so it is really hard to twist.


#3

I wondered about that too. Perhaps the software would cut power for say 2 sec to signal a fault and then allow power to the working motors so you could still fly.


#4

My feeling is that an engine quitting would cause less twist than a wingtip collapse in a thermal. As pilots we’ve all been taught what to do, weightshift heavily and promptly, and are used to reacting to such. Unless you’re taking off and actually still running in contact with the ground it shouldn’t be a biggie so I think adding to the software load is more than it’s worth. If you really want to do it anyway how about this. Make both upper props turn CW and both lower props CCW. If a motor fails then get the software to only kill power to the opposite prop, ie, left shoulder motor goes: right hip motor is cut. That way you will still have thrust from two motors, thrusting through CoG and with opposit torque.

Paul in Oz


#5

Thanks for the replies guys. Interesting stuff.

The only problem I see with completely cutting off a good motor on the other side is that you are now demanding high power levels from the 2 remaining motors, perhaps for an extended period, slightly increasing a risk of a failure of either motor’s ESC. If you leave 2 motors running on the “good“ side, they can be made to run at a lower power level to match the single remaining motor on the failed side. Admittedly this motor will be running at a high power level, but I guess this is unavoidable.


#6

The motors and ESC shouldn’t have any problems running at full power as they were designed to do so. Also, say one motor goes out your probably going to head back to land, which is something not possible if your gas motor goes out.


#7

It isn’t as much of a problem because of the torque created by the motors spinning (because they are spit up and small) as much as the leverage of the trust from the motors, but I know what you’re saying.


#8

First post. Excited to be here.

I don’t see it as a flight issue having one motor out with the 4 prop design. There light props so torque twisting should be negligible. 25% power reduction shouldn’t be a big issue compared to an entire motor out. Then again I’m speaking out of speculation having never flown this configuration.


#9

I tested the Revolt with a motor off, in flight it is not even perceptible regarding the tendency to twist.
At the takeoff, instead, I strongly discourage anyone else trying because in my experience (maybe due to the low speed and low load) as soon as both feet are lifted off the ground the tendency to twist is very aggressive.


#10

That’s good to know. Does this mean that there is no need for you to do anything fancy in software, such as reducing power on the motors on the other side?

That would simplify things, and also mean that you could have full power available on all 3 remaining motors if needed for flight reasons.


#11

Well, the take off is a crucial moment and I prefer to have a software that can handle any kind of failure.
Take a look at this topic https://community.openppg.com/t/separated-vs-parallel-which-is-better/26/6?u=gla.torg
Remember that a “failure” can be a simple cut-off because the batteries are low.
Other kind of failures that I experienced:
-bad connection on one ESC
-Propeller not fixed well to the shaft


#12

This one would not even register as a failure to the flight controller unless the RPM ramp-up is monitored.


#13

I think that monitor the current and/or ERPM can tell you something. Basically the output power (watts) and rpm can do the trick.


#14

Hey :slight_smile:
What’s the flight time with the new engines and thrust?


#15

They have the same thrust (165lbs) and there a little more efficient. I haven’t got to fly them yet :expressionless: but from the test, i have done I expect to see about an 8% increase in flight time. Also, they are 40% lighter weight so that nice knocks off about 4lbs.


#16

so about 5min more? total flight time 55min? I guess


#17

We will definitely do this in the FC code.