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Hi all, haven't posted much on this forum, to be honest I forgot I was a member :P

I have an askman mount for my Trex 600E, it is the pan/tilt version with robotic servos. I am trying to sort out the tilt with a gy401 gyro, so that when the heli accerlates/decelarates the camera will remain level. So far I am NOT having any luck :( The mount tries creeping backwards on it's self as soon as I connect the gyro. Should the gyro be on the gimbal or the mount is what I'm wondering here? Also maybe I should change the servo instead of the robotic 360 degrees servo?

Anyone have a clue as to what I am doing wrong...sorry it seems a rather general question, my apologies.

Ross

Edited by Macsgrafs

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Hi Ross,

the gyro should be mounted on the heli and the neutral point adjusted so that is dose not creep.

It will always drift/creep up to a point though as it has no reference to stop it.

Terry

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Another solution that usually works well IF the mount is good quality with little slop is to mount the gyro on the moving part (attached to the camera) and use the gyro in heading hold mode. That requires connecting the gain adjustment wire to a free channel on the RX and adjusting it properly to have good stabilisation performance without oscillation.

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Thats interesting Kilrah, I have never had any luck that way round, the mount always gets out of control and shakes itself mad. Please note HH mode is required when you mount the gyro on the heli too.

Terry

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Yeah as I said there needs to be no slop, the mount must be of high quality. I've only tried it on geared mounts with servos modified for continuous rotation so they don't act as a servo anymore but just as a speed-controlled motor. I'd believe problems would arise when the servo's regulation is also introduced in the loop...

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Thanks Terry & Kilrah,

I have it mounted vertically on the moving part, but it judders itself to death!!! Someone on another forum mentioned that the gyro has to be hard mounted as such to prevent this, which if I hold the gyro tightly against the mount seems to work. Mounting on the heli would be hard, don't forget the mount rotates 360 degrees & more, it will keep spinning all day (robotic servos) so the leads would soon snag & rip out :(

There must be a way...got my thinking cap on, but need something in my head to make it work :D

Again thanks for the replies guys, will keep experimenting

Ross

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Ahh I think I see. If you have a standard servo then it needs to be mounted on the heli and if you have a modified servo (will not return to centre when the stick is released) then it should be mounted with the camera.

Terry

Edited by Terry

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Ahh I think I see. If you have a standard servo then it needs to be mounted on the heli and if you have a modified servo (will not return to centre when the stick is released) then it should be mounted with the camera.

Terry

Tried both ways Terry & still its creepign about, it seems to get off on the judders BIG time!

If all else fails I will resort to my favourite tool of choice.....the Hammer :lol:

Ross

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You said you have a robotic servo, maybe try a standard servo ?

Mount the gyro on the heli.

Set the gyro to HH mode, adjust the neutral point so it dosesnt creep and set the gain low.

Terry

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Good idea Terry, will buy a standard servo & use that, I' sure it's because it's a robot servo with no centre that's causing the problems.

Ross

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Hmm, little summary needed:

1) Gyro on the heli (non moving part) and standard servo: Won't work, regardless of HH off or on.

2) Gyro on heli, modified servo: OK, but with HH off only.

3) Gyro on camera, modified servo: OK with HH on or off.

4) Gyro on camera, standard servo: OK with HH on.

In situation #1 with HH off, when the heli is tilted the gyro will give a temporary correction that depends on its angular speed, then as soon as the heli stops in its new tilted position the servo will return to its normal state and not stabilise anything. An integrator is missing in the loop to accumulate the gyro's correction and translate it into a angular change for the camera. Using a modified servo solves that (#2), but requires precise gain tweaking for the correction to match the initial movement. With HH on, what the gyro wants to do is to keep its own angular position constant. So when the heli is tilted, it will try to act on the servo as much as needed until it comes back to its original position. But it will never happen, as moving the camera servo will never move the heli itself (that's where the gyro is mounted, remember). So the only thing that will happen is that the gyro will push the servo directly to its end point in either direction if it's a standard one, resp. make it turn indefinitely if it's a modified one until the gyro comes back to its original position.

#3 with the gyro on the moving part you can do all you want. This is actually the situation that matches the common gyro usage on a heli. The gyro IS on the part that moves (usually the heli), and measures its movement. To go even further, on a heli when the gyro acts on the tail rotor, when it moves the servo this will result in a certain angular speed for the heli that is proportional to the servo deflection. This situation is reproduced when a modified servo is used to drive the camera. So just like the original gyro's purpose to stabilise a heli, you agree with me that HH can be on or off, performance being better with it on.

Now for #4, a standard servo can be used too, because anyway when HH is on, the gyro will continue to act on the output to maintain its position. However, as we're not anymore in the configuration the gyro was meant to be used for in the first place (one extra integration) the response won't be ideal. With HH is off we'd just get back to a situation similar to #1.

So, based on this the best solution (or at least the one that matches best the gyro's intended use it has been optimised for) would be to have the gyro on the camera mount, with a modified servo (or standard one with servo integrator, which would have the advantage of keeping the limits and avoiding full turns) and HH on.

Edited by Kilrah

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I can only say what I have found useing a csm gyro in HH mode worked well set up as in #1.

The gyro on the heli moved the servo an amount equal to the tilt of the heli and so kept the camera level.

When mounted on the camera as in #4 the servo wagged it self mad. I too thought this setup would be as it would normaly be set up as a tail gyro and so work fine but it did not for me. I have only used a csm gyro so it may be to do with that I don't know. It just over corrected no matter how I set the gain.

Terry

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Again, many thanks to both of you nice gents. Such a big reply Kilrah, I have had a good read & what you say makes sense in the written world, but like Terry I am having serious judder problems in the real world. I'm going to buy a single standard servo today & when it arrives swap it out with my robotic tilt servo & try all again. At the end of the day I only need 90 degrees down swing max, so it should be fine. I am relating the gyro location as regards to how a tail gyro works, but your input guys is very much appreciated & I wonder where would be the best place on the gimble? I have attached a quick photo I took just now as doing this reply.

Regards & thanks

Ross

post-4179-1217933565_thumb.jpg

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Well as I said I vote for mounting it on the heli, Kilrah says where you say which I admit seems correct but it didnt work for me.

Terry

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Well as I said I vote for mounting it on the heli, Kilrah says where you say which I admit seems correct but it didnt work for me.

Terry

I do agree with you Terry, I have tried it on the lower arrow spot & it judders like a Bitch! I was trying to work things out as though the pivot screw is the main rotor mast & knowing that a gyro needs to sense movement for it to work correctly, but it doesn't & I am putting that down to the type of servo..no neutral point.

Have ordered a futaba S3152 from SMC (Special price at the moment) & hope it will give me a cure, then I can inform you all as to yes or no ;)

Ross

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