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Author Topic: Moving Heads keep ending up off-target??  (Read 593 times)

Shane Crabtree

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Moving Heads keep ending up off-target??
« on: October 18, 2017, 12:57:26 am »

Okay, so I have four moving heads which sit on the floor in a row. Lets say I have all of them pointed at an object on a wall in one scene. I run through a couple of other scenes where the heads are performing rotational or random movements of some sort. I then go back to the original scene where the heads are pointed at the wall object, only this time they're all off target by a few inches or more.

I'm wondering whether or not this is a result of the motors in the heads moving quickly and then coming to a sudden stop? Almost as if the motors/belts inside nudge off axis just slightly due to all the movement..? I've gone through most all of my scenes and changed the fade time for them to about a half second, and that seems to have helped a little, so they aren't just ram-jamming into the next scene to a sudden stop.

But I still have a couple of scenes where there's a lot of fast rotational movements, which seem to throw the lights off their targets about an inch or so. Would it be wise to reset those chase durations to something a little slower to help remedy that? Just looking for thoughts, opinions and tips. Thanks
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Tom Bourke

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Re: Moving Heads keep ending up off-target??
« Reply #1 on: October 18, 2017, 01:39:01 am »

Once you fix your name per the forum rules we may be able to help.  Other needed info is what lights, controller, and if applicable light mode.
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Shane Crabtree

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Re: Moving Heads keep ending up off-target??
« Reply #2 on: October 18, 2017, 08:44:09 am »

Once you fix your name per the forum rules we may be able to help.  Other needed info is what lights, controller, and if applicable light mode.

...30w Mini LED moving heads running through myDMX Buddy 2.0 on DMX mode.
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TJ (Tom) Cornish

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Re: Moving Heads keep ending up off-target??
« Reply #3 on: October 18, 2017, 08:54:11 am »

...30w Mini LED moving heads running through myDMX Buddy 2.0 on DMX mode.
Shane, either there is mechanical slip happening on a belt, or your lights do not have encoders on pan and tilt, meaning the fixtures have no way of knowing how far they have actually moved.

Going out on a limb, these are probably low-cost Chinese fixtures, and this is an example of getting what you paid for/not getting what you didn't pay for.  You may be able to open up the fixtures and see if you can put a little more tension on the pan belt by adjusting the pan motor mount, but other than that, slowing your pan moves is about all you can do.
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Shane Crabtree

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Re: Moving Heads keep ending up off-target??
« Reply #4 on: October 18, 2017, 10:22:18 am »

Shane, either there is mechanical slip happening on a belt, or your lights do not have encoders on pan and tilt, meaning the fixtures have no way of knowing how far they have actually moved.

Thanks for the helpful reply! You are correct, these are Lixada mini's. They're pretty good little units just using for my wedding, but buying cheap Chinese, I sorta figured what I was getting myself into. I'll take your advice and crack them open tonight to see about those belts. Slowing the scene fades even by half a second fixed a lot of it, so I could also try slowing the effect transitions mid-scene.
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Tom Bourke

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Re: Moving Heads keep ending up off-target??
« Reply #5 on: October 18, 2017, 01:53:33 pm »

It could also be under powered stepper motors losing steps.  Do they have a homing function other than at startup?
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Shane Crabtree

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Re: Moving Heads keep ending up off-target??
« Reply #6 on: October 18, 2017, 06:02:17 pm »

It could also be under powered stepper motors losing steps.  Do they have a homing function other than at startup?

Not that I am aware of, but shouldn't there be a way to check that?
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Tom Bourke

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Re: Moving Heads keep ending up off-target??
« Reply #7 on: October 18, 2017, 06:08:40 pm »

Not that I am aware of, but shouldn't there be a way to check that?
If there is one it should be documented in the manual.
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Shane Crabtree

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Re: Moving Heads keep ending up off-target??
« Reply #8 on: October 18, 2017, 06:54:47 pm »

If there is one it should be documented in the manual.

Just looked through it. Doesn't seem to be any sort of onboard calibration other than start up, when it goes through its' self check. Took one apart and tightened the belts a little bit, went through scenes and changed fade/effect times. Going to put them through their paces and see what happens I guess.
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Jeff Lelko

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Re: Moving Heads keep ending up off-target??
« Reply #9 on: October 18, 2017, 07:25:52 pm »

Did you also make sure the belt's gear/pulley is tight on the motor shaft?  I've had one or two instances where the set screw came a bit loose and caused the affected parameter to drift.  Aside from that and what you already tried, this is unfortunately one of the common issues with low-dollar moving lights.  Drifting a few inches isn't horrible though - I've seen much worse from generic fixtures, to the point that it can't hit the same location twice!  There's a reason why some lights cost $100, some $1000, and some $10,000...  Best of luck though!
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Paul G. OBrien

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Re: Moving Heads keep ending up off-target??
« Reply #10 on: October 18, 2017, 08:15:57 pm »

Okay, so I have four moving heads which sit on the floor in a row.

Another possibility here, these heads don't weigh much and sounds like they aren't attached to anything so check that they aren't just twisting on the floor, it wouldn't take much movement of the base to change the spot position 20ft out a couple inches.
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Shane Crabtree

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Re: Moving Heads keep ending up off-target??
« Reply #11 on: October 18, 2017, 09:19:53 pm »

Did you also make sure the belt's gear/pulley is tight on the motor shaft?  I've had one or two instances where the set screw came a bit loose and caused the affected parameter to drift.  Aside from that and what you already tried, this is unfortunately one of the common issues with low-dollar moving lights.  Drifting a few inches isn't horrible though - I've seen much worse from generic fixtures, to the point that it can't hit the same location twice!  There's a reason why some lights cost $100, some $1000, and some $10,000...  Best of luck though!

Thanks! Yes, I've opened the first one and made sure the pan/tilt belts were tight. Had to pull just a bit to take a little slack out. Didn't do a lot to fix the issue, so I've gone through turning it on & off and doing tests with that, with both my DMX software open & closed.

Seems the issue arises when I turn on the unit, it goes through it's first initial panning check, and goes to Zero like normal, before I start any scenes. It's almost like it resets its' own XY parameters so that it goes way too far off target when I start up the first scene (pointing at a mirror ball.)

It's got one of those little spindle catch things around the panning gear that hits a sensor switch to start over when it's reached its' maximum pan rotation. I then tried creating a "calibration" scene, if you will, with some wonky rotation effects. After running that, I reverted back to my first initial scene, and it had at least moved the beam over the mirror ball.

Sooo, anyone have any good ideas for calibration-type scenes?
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Shane Crabtree

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Re: Moving Heads keep ending up off-target??
« Reply #12 on: October 18, 2017, 09:22:28 pm »

Another possibility here, these heads don't weigh much and sounds like they aren't attached to anything so check that they aren't just twisting on the floor, it wouldn't take much movement of the base to change the spot position 20ft out a couple inches.

Thanks Paul. To remedy that possibility, I've put masking tape on the floor at the corners to check whether or not they're moving. There doesn't seem to be any noticeable difference. Any tips on weighing them down just in case?
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Mark Cadwallader

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Re: Moving Heads keep ending up off-target??
« Reply #13 on: October 18, 2017, 11:45:05 pm »

Thanks Paul. To remedy that possibility, I've put masking tape on the floor at the corners to check whether or not they're moving. There doesn't seem to be any noticeable difference. Any tips on weighing them down just in case?

A old skool approach is to make a simple plywood and 2x4 base plate for the fixture to be bolted down upon. (Use the threads that are there for attaching an O-clamp.)  The added mass and friction will decrease any tendency for the fixture to "walk".

Slowing down the speed of movement will, as you found, increase the accuracy of positioning.  You are more likely to be able to stop your car exactly 12" from a wall if you are driving at 10 mph than if you are approaching at 30 mph.
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