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Old Jan 06, 2013, 05:37 PM
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Joined Dec 2007
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Help!
Strange gimbal movement - ideas ??

Heya folks,

After some trouble-shooting ideas regarding some funky gimbal movement im getting

basically the system is 2 axis, 2:1 belt drive on both axis, all ball bearing pivots, analog hitec hs82mg (0.12sec @ 6v) metal gear servos (new) running at 100Hz and 6V through a separate BEC, control through my naza.

there is zero mechanical slop in the system. gear backlash in the servos is minimal, but it is there.

problem is when rocking the frame from side to side, ie rolling from left to right repeatedly, im getting a lag/delay at the very moment the roll changes direction. you can see this quite clearly in the first video below.

the gain settings are otherwise spot on, the horizon stays level and controlled the rest of the time, but there is def something funny going on!

i kow the naza isnt great, but i havent heard of other people complaining of this particular problem, and im otherwise quite happy with how the naza is driving things.

so yeah.... the question is! - is this a control problem (ie naza is crap) or is it a servo problem (ie crap servos) or have i missed something altogether and theres something else i could be tweaking?

cheers
ed

latest video @ 100Hz after i tried playing with a few things to see if i could improve the lag. best demonstrates the lag issue during rocking from side to side:

Ed's IAISS Y6 - fine tuning 2 (0 min 38 sec)


and the following is my first video from earlier today @ 50Hz wheni first fine tuned the gimbal for the first time. im pretty happy with how it works in generally, just that lag during rocking motion has me stumped!

Ed's IAISS Y6 - fine tuning (0 min 32 sec)
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Old Jan 07, 2013, 05:51 AM
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crezzee's Avatar
Worcester UK
Joined Nov 2004
761 Posts
You will always get lag with this type of gimbal because the gimbal can only react to a movement once it detects a movement from the platform. The only way to get rid of all lag is to use weight and gravity to help keep the camera steady like in these 2 systems:

http://ecilop.tv/shop/ecilop_easy.phtml

http://www.foxtechfpv.com/glyder-600...ies-c-141.html

These systems have springs on the gimbal servos to allow gravity and weight to over-ride the inital servo lag.

Faster digital servos will help on your gimbal but you will always see a small amount of lag.
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Old Jan 07, 2013, 09:38 AM
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hmm, true... thought it still strikes me as an excessive lag/twitch, and something that ive not seen from gimbals of similar design

on the counterweight theme - this gimbal WILL use something excatly like you describe... the battery assembly is hard-mounted on the roll-axis shaft. though its not yet assembled in these videos as i was trying to get the systme optimised/tuned first, before adding in the passive roll component (whcih will then require a retune, but ill know my starting points a bit better)



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Old Jan 07, 2013, 04:58 PM
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update, i tried the counterweight... no change in the lag character

its like the controller 'loses' the true horizon a few degrees on direction change, or the servos have a massive deadspot

will try swapping a few components out to see what happens
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Old Jan 07, 2013, 05:15 PM
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Worcester UK
Joined Nov 2004
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Quote:
Originally Posted by ed_jza80 View Post
update, i tried the counterweight... no change in the lag character

its like the controller 'loses' the true horizon a few degrees on direction change, or the servos have a massive deadspot

will try swapping a few components out to see what happens
The counterweight will only work if you introduce some sort of flexible servo connections to the gimbal so it can initially stay where it is. The 2 systems i mentioned earlier use springs to allow movement. Look closely at the designs particularly the servo connections to the gimbal.
I promise you there is no problem with your gimbal it looks like it works as it should.
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Old Jan 07, 2013, 05:43 PM
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You have analog servos?. I could be wrong but I think the NAZA prefers digital servos?
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Old Jan 08, 2013, 03:52 AM
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yeah, thinking of swapping in some Hitec (cheaper digital) HS5084MG servos (about equivalent to the HS82MG in size/spec) and although not programmable, has a deaband of only 0.002s and is about twice as fast @ 6v as the HS82MG (which has a deadband of 0.008s which is on the slower side)

i also agree regarding the passive and active stabilisation systems fighting each other when rigidly fixed. thats something i noted last night - quite apparent actually. but the complexity of a flexible linkage allowing a free range of independent motion... especially in a small space, its a bit of a headfuck!
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Old Jan 09, 2013, 09:42 AM
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Which gimbal is this? I'm looking for a gimbal for my 450 and was looking for suggestions. Hopefully changing to digital servos will do the trick for you
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Old Jan 09, 2013, 12:58 PM
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Hi, i made it myself

cheers
ed
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