Camera mount servos

[Bartman]

Well, my buying binge continues. I've got potential work for the new copter so the camera mount can't wait. at the averticalview.com website they sell Hitec 645MG servos but these are notorious in the giant scale plane community for having a sloppy centering instinct. in other words, they don't reliably return to center perfectly time after time after time.
I've seen talk of slow servos, analog servos, high torque, low torque but what is optimum? I'd guess a slow servo with adequate torque but not too much, plastic gears (metal maybe??)
Anyone (Denny??) care to chime in?
Thanks,
Bart

 

[Bartman]

something like this maybe? i wonder what the torque requirement is?

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXDWF8

 

[Droider]

Yo Bart.. I think I read somewhere that Jeoffscoll is using them on his PH mount but analogue ones not digital..

I intend to look more in to the servo issues when I have my ADX up and flying again..

DAve

 

[Emowillcox]

Hey Bart.. good topic.. was doing some research recently and here is some info I found.. I think I got most of it from the PhotoHigher web site


servo can be important for smoothness



IMHO EMAX
http://www.valuehobby.com/product_details.php?category_id=20&item_id=105

http://www.valuehobby.com/products.php?category_id=20

..................................
\The servos included with the mkTR Professional are good for cameras up to about 450g (1lb) in weight. For DSLR cameras like the Canon 550D or similar it is recommended, but not required, to use the optional High Resolution/High Torque Hitec HS7985MG servo. The HS7985MG uses Hitec's new G2 protocol which is 2X the resolution. Essentially, twice the number of steps per full sweep. Also the torque output is over 2x that of the standard servo. The result is smooth fine and powerful tilt motion. We recommend when using the HS7985MG that you also replace the 5.0v Recom voltage regulator for a 6.5v Recom voltage regulator on the servo bus of the Mikrokopter FC board. This will allow the full potential of the HS7985MG servo in speed and torque.

one more

http://sexycopter.myshopify.com/collections/frontpage/products/g01

other ideas
TowerPro MG90, Hitec HS-65HB, EMAX ES08MD servos

 

[Bartman]

thanks Mike and Dave. Since the servos won't be controlled by the MK flight control board that leaves me with a few options. I could power the mount's FC and servos with a 1100 mah A123 pack which is both weight efficient and the right voltage for the servos, CC board, and video Tx. That would put them on a very reliable and very appropriate power supply while optimizing the servo output. Servos can be powered directly from the battery and just have a control input from the board so there's no RECOM or regulator to worry about. At least, I think that's the case.
thanks for that Mike!
If I'm wrong on any of this please correct me.
as far as that servo though Mike, it's digital which is a no-no according to the brains at multirotorforums.com
hmmmm maybe the OpenPilot guys can add to the conversation, can the CC board control a servo with higher resolution and maybe eliminate the digital servo jitters?

 

[jes1111]

Can't imagine why digital servos would be a no-no - maybe some interference issue on the MK? Digital servos have so many advantages over analog - especially the Hitec models with G2 (faster reactions, higher resolution). Certainly CC can drive digital servos (at up to their 333Hz maximum). As to resolution, CC doesn't care about the resolution capability of an actuator (be it a servo or an ESC) - it issues position commands in "integer" µs units (e.g. 1488µs).

I don't know if a digital servo will accept a "fraction of a µs" (e.g. 1488.25µs) - Denny will know, and James can no doubt explain the CC end more thoroughly

 

[Bartman]

the belief regarding digital servos is that they are hyper determined to maintain center which manifests itself as vibration in the video display. you wouldn't see the effect of a servo on amphetamines if you were only flying planes but with video, where every little stutter is obvious, it may be part of the problem as to why we're falling short with aerial video. it's just a theory. for $100 i may try the new Hitec with my franken-mount to see if it can all hold together. is the fate of the free world hanging on it? not really but it's an interesting theory and a fun experiment to work through.
bart

 

[DennyR]

Jes
Many top of the range servos have 12 bit/ 4960 possible positions across the us range of 1000 to 2000 signal so yes is the answer. IMU's such as Picloc have .1 us resolution. I have not tested V3. I just hope it is a whole lot better than the previous models which I feel did not do George M's. reputation any favors. !

I am guessing that with a 12 bit ADC, CopterControl would also have sub 1us. resolution. Peabody, over to you!

 

[ZAxis]

I'd definitely recommend the Hitec 7985MG. I have just bought a couple for my homemade camera mount. Lots of torque, fast smooth action and high resolution.
I also bought a Hitec HFP20 servo programmer which allows you to set speed/travel/resolution, etc on the servo. It also allows you to manually test the servo, twisting the control knob moves the servo from one end to the other of its travel. So you can debug your gear before going near any FC or any other on board electronics.

 

[Macsgrafs]

Franken-mount love it Bart.

 

[DennyR]

I also found this useful http://fpvhobby.com/74-two-camera-switch.html

 

[mbsteed]

I have a MKPro PhotoshipOne and it came with a HS7985MG for tilt. I haven't got it airborne yet but check out the bottom of the following page for more information:

http://photoshipone.com/products/mktr/

 

[midnight999]

I'm sure I read somewhere that digi servos apply max voltage for every movement, resulting in very quick reaction times, however analogue varies the applied voltage according to the extent of movement required, eg, small movement lower voltage. this results in slower, but smoother reactions that are desirable in a gimbal.

 

[Bartman]

I also found this useful http://fpvhobby.com/74-two-camera-switch.html

what does it do Denny?

 

[jes1111]

The Hitec HS-M7990TH would seem to be the dog's whatsits of servos - magnetic encoder (so "4x resolution" compared to a regular servo), powerful, reasonably quick. I view this like a car's engine: you don't necessarily need the top speed, but you want plenty of "grunt" (torque) to make acceleration smooth and effortless.

Yes, digital servos apply the full voltage, but pulsed so that the average voltage is lower. They certainly don't go from zero to full speed instantaneously: the firmware "ramps" the speed to achieve smooth acceleration and decelleration. Digital servos are the way to go, for sure.

 

[RC Flying]

Did you make any nice discoveries regarding servos in the end? I know it's quite an old thread but it comes up top in google for what I'm searching for.

I have noticed I get those little stutters in my filming on a little gopro mount, but only at 30fps. If I film at 60fps it seems to go away - is this possible? Could it be the extra frames smooth out the stutters because you aren't jumping as suddenly from one aspect to another?

 

[Bartman]

I tried Hitec and in the process of switching to 2 cell Lipo power for my mount it was discovered that Hitec servos don't do 7.4 volts very well. Other servos like JR and Futaba are very expensive so I've been using Savox and am very happy with them.
What little stutters are you talking about? some movements of the camera just can't be avoided if you're out flying and not being exceptionally careful. it's all quite a mystery but with time things can be improved. you could always downgrade the video from 60 fps to 30 fps after it's recorded, no?

 

[RC Flying]

Thanks for your reply. The stutters are definitely from the mount and not the flying. I mean tiny little jerky movement, like little wobbles, in the pitch axis. Anyway I'm going to try a different mount today, and 60 fps instead.

 

[Stacky]

I have been finding that if there is any slop in my linkages it can show up as stutter and also if there is any slop in the servo gears. I have Savox servos in one small gimbal with metal gears and i have been warned that these will seem good at first but over time will develop slop. That hasnt happened yet but on another small gimbal I have Align servos with plastic gears. At this point the plastic gears seem to have less or no slop than the metal geared ones but it might just be all in my mind the differencs being so small.
Also I think I have found the stutters are also affected by vibration, so that any slop in my linkages seems to affect the stutters even more. At this point Im not using belt driven roll and tilt but the old rod type. So many things to learn and understand....