Gimbal Digital Servo Smoothness - Ports 10,11 and 7,8 - Discussions

I have been working with getting my gimbal setup using my APM2. I tried both analog and digital servos and can not get smooth movement. I tried a high end KO and another high end Futaba digital full size servo and both were twitchy during movement. I went thru the gimbal and made sure everything was free moving and still get the jerk in the movement. I tried a different gimbal using mini servos that are brand new hitec 5805MG Digital servos. Testing them outside the apm connected straight to an rx they are butter smooth, same with the full size servos I tried. Once connected to the APM I get this jitter. I tried both the 50hz output on 10 & 11 as well as the higher output on 7 & 8. Both get me the same results. I am powering the servos with a ccbec at 6v. All I am getting from the APM is the signal. I also have my pot trim knobs assigned on my radio to adjust level in both axis. The gimbal works great, it is just the output going to the servos from the APM.

I am 2.9.1 for my APM firmware. My question is this...

Since the gimbal output is relative to the output for level flight cold it be that by adjusting PID's for a less "tight" machine loosen up the gimbal a little? It almost seems too sensitive. Another way to word it would be, would adjusting the stab PID and the rate PID have any effect over the gimbal outputs?

Is there any way to smooth the output and/or raise the hz rate coming from the APM?

I kinda need this working for this project as this is a small quad with a built in gimbal. Adding another controller just for the gimbal is out of range for the project. Any help would be greatly appreciated.

Should I post a log?

Hi Wes,

My friend Oliver is experiencing the same problem and at this point it seems likely that the problem is related to the APMs 50 hertz update rate (this is true on both the slow and the fast channels).

It doesn't do you any good to have 400 hertz servos if the are only getting updated at 50 hertz.

Basically it makes the problem worse.

If you update a fast servo too slowly it gets to the location and stops then jumps to the next location and the continuous start stop causes the jerkiness.

You actually need a high quality analog 50 hertz servo (with a tight gear train) to get smooth movement on the APM.

Digital servos are way too fast and good analog servos with minimal gear lash work the best right now.

I am not sure this problem is at all likely to be fixed on the APM as it is very low on both program space and extra processor performance capability, but my guess is in a few months the extra resources of the PX4 will permit a definitive solution for this.

Replies

Wes Brown March 20, 2013 at 5:22pm

I just flew two more packs thru the machine and really tried to push it harder. I could see the apm trying to keep up with where the Gimbal needed to be. Clearly the apm just isn't up to that much multitasking. This is disappointing as my whole reason for the apm was to have a platform capable of a broad set of tasks. I feel like I spend more time tuning then flying sometimes..
Mike Mac March 20, 2013 at 4:13pm

I am ready for the APM 3 with a faster processor and more memory.

Are any of the beta testers or developers flying them yet?

I don't like the layout of the PX4.

.
Wes Brown March 19, 2013 at 5:50pm

Thanks Gary for the reply. That does make sense but I don't like it.. lol. Trying to find an analog mini servo that's not sloppy or poorly made is going to be tough. I'll go by the lhs tomorrow and see what I can come up with. Any recommendations for something from hitec? The servos I'm currently using are hitec 5805mg so it needs to fit the same hole. Thanks again. :)
Gary McCray March 19, 2013 at 5:19pm

Hi Wes,

My friend Oliver is experiencing the same problem and at this point it seems likely that the problem is related to the APMs 50 hertz update rate (this is true on both the slow and the fast channels).

It doesn't do you any good to have 400 hertz servos if the are only getting updated at 50 hertz.

Basically it makes the problem worse.

If you update a fast servo too slowly it gets to the location and stops then jumps to the next location and the continuous start stop causes the jerkiness.

You actually need a high quality analog 50 hertz servo (with a tight gear train) to get smooth movement on the APM.

Digital servos are way too fast and good analog servos with minimal gear lash work the best right now.

I am not sure this problem is at all likely to be fixed on the APM as it is very low on both program space and extra processor performance capability, but my guess is in a few months the extra resources of the PX4 will permit a definitive solution for this.

This reply was deleted.