Servers by jDrones

Servo compatability for tailrotor

Hi again,

I plugged in a Futaba S9256 digital servo for the tail rotor in channel 4 and it did not power up. This is a monster tail servo designed for the GCY611. Can a servo with a 760ms center be used? I searched and I did not find a compatability list.

I switch the tail servo to a JR 8700G super servo and it seems to work ok. it seems a little active around center like the frequency is a little high but it works ok.

the JR8700G is a strange one, it is not a true digital kind of a hybrid. The motor is still driven by the reciver like an analog servo if I remember right. I have used it with no problems on a BeastX configured with a frequency of 270hz. Can the frequency be changed for a specific PWM output?

so,

Will Pixhawk support servos with a 760ms center like most of the current tail servos on the market?

and

Can the output frequency be changed.

thanks again

BV

You cannot use 760us servos with Arducopter unfortunately. Something I’d like to do but, not yet possible.

On the 8700, the default PWM speed is 125hz. You should be able to change it, but I haven’t played with that myself very much. There’s a parameter called RC_Speed which controls this.

Thanks again Rob I know you are a very busy.

I notice the RC_Speed in the parameters, I did not see it in the channel 4 parameters so I assume it is a global setting and I did not mess with it.

It smoked after 10minutes or so sitting on the table powered up. Not exactly a typical servo, no biggie, I had it on the bench so I thought I would try it. Also, my hell tail is not in heading hold mode, not sure why? I read the other post where it was solved, but late at night I could not figure out what solved it. Some code was posted and my brain shut off.

Any servo suggestion for a proven tail?

My tail acts like a low gain rate gyro, almost no compensation. I spooled the hell to test the flight modes, and I had to hold half stick to keep the hell from spinning with no main blades. I still have only one mode “stabilize” that give me collective and cyclic control. All other modes I have no control main rotor control except for the tail.

Almost there,

Best regards,

BV

Can you just send me your parameter file? Seems like you have a lot of things wrong.

Late reply, but I just saw this thread after a search on the subject. I have bought a KST BLS805X HV servo for a heli tail servo and I want to use it with Pixhawk. The servo spec is 760uS 666Hz. I assume (and hope) that 666Hz is a maximum and that is will function ok at 200Hz or 300Hz.

Looking at APM, what if I set :

HS_min : 500uS
HS_trim : 760uS
HS_max : 1000uS
RC_Speed : 300Hz

I can’t see why this would not work, but I’m sure you are are going to tell me!

P

Hi all,

i’ve struggled with the same problem time ago, when i had a project to make an autonomous UAV out of a 700-class heli.

Here’s the answer from Chris Olson about 760us servo compatibility:

https://discuss.ardupilot.org/t/arducopter-does-not-work-what-im-missing/23766/15

story short, “doesn’t make sense to add 760us compatibility because those servos aren’t meant to work longer than 3-4 mins of flight due to overheating issues”.

It remains a puzzle for me why you cannot set a single Pulse width and frequency PER servo/PWM output (like LibrePilot does, for example). It would be a big step forward in development of such flying machines.

Should i open an issue on the official github maybe?
EDIT: done it, hope they take it into consideration

Already taken into consideration. I put the proper labels on your feature request and we’ll look at it. Part of the problem in heli is that we share libraries with multirotors. So what is implemented for one has to work for the other.

This topic of 760uS servo not compatible with ardupilot seems not have been resolved. I can confirm that the 760uS tail servo DOES NOT just burn up if used longer than 4 minutes. I have helicopters that fly for an hour on these servos just fine and the only reason they would burn up is binding. With that said, why hasn’t this problem been solved yet?

ArduPilot can set the servo pwm to work with 760us centered servos. I use a normal cyclic servo for the tail on all my UAV’s and those cyclic servos work perfectly fine on a UAV. Those narrow band, high frequency 760us servos were/are a marketing fad that many people bought into. If 3D heli pilots had any common sense they would realize that you can achieve the same thing with a much cooler-running low-frequency servo by moving the linkage ball further out on the servo arm. The best engineered products rarely succeed in the marketplace. The best marketed ones do :grinning:

We as 3D heli pilots and engineers have tried every combination of systems to gain better controls on competition quality helicopters. Yes, you can use a cyclic servo on the tail but don’t let the reason be, “the servos fail after 4 minutes.” 760uS servos work better in adverse conditions and certain 3D maneuvers.

IMO 760us centered servos are not a good choice for UAV. I flew a few of them and never had one last more than 25 hours. 25 hours is an eternity in 3D flying. Our survey helicopters get 25-30 hours a week put on them during the peak of the season. I adjust the yaw rate on our UAV’s to not exceed 120 deg/sec, the larger ones are 90 deg/sec.

If you like 760us servos, then bolt them on. ArduPilot supports them. Just be careful when firing up the system for the first time because the default center is set 1500 trim, 1100 low, 1900 high. If you don’t adjust the settings before putting your 760 servo on and plugging it in you will burn it out.

Servers by jDrones