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Re: Reducing DEC Backlash with Titan 50

 
Edited

Hi Dan,

Glad to hear you're making progress with backlash!

The sound appears to be caused by too tight of a mesh between the worm and the worm-wheel. Very tiny variations in worm and wheel can lead to increased binding which results in the occasional whiney noise. Also double-check that everything is well-balanced, the mount may be struggling under uneven weight distribution. Also, make sure the worm is properly greased, dry spots can also cause binding.?Here's how I adjust the worm mesh on a Titan (originally posted here /g/Losmandy_users/message/50534):

1. Loosen both of the wing screws on the axis you are adjusting

2. Loosen slightly one of the large bolts holding the worm assembly underneath and push the whole assembly very slightly out, away from the gear.

3. Try moving the motor with the HC to see if the axis now moves freely, without stalling or binding. If it doesn't, move the whole worm block even further out. Very little movement is needed here.

4. Once the motor is moving freely, tighten the large bolt but not excessively, enough so that the worm block can still be pushed with some force.

5. Test the motor again with HC. If it binds now, repeat steps 2-4 moving the worm slightly further out

6. Now, tighten both wing screws by the same amount, just enough so that they are not loose anymore, only until you feel some resistance

7. Test that the motor rotates freely. If not, go back to step 2 and try again.

8. Now, check for backlash. If there is too much, tighten the wing screws a 1/8 of a turn more, rotate both screws by the same amount. They should be harder to turn, as they are pushing the worm block closer to the gear, against the friction caused by the large bolt

9. Repeat steps 7 and 8 until just a little backlash is left.

10. Tighten the large bolt, but don't overtighten. When final tightening this, it can push the worm just a bit closer to the wheel. If there's no more wiggle room, it can cause the worm to bind. I usually leave a little more backlash than I'd normally like at this point, so that when I tighten the large bolt, it takes up some of the remaining slack.

This usually takes about 5-10 minutes, and my adjustment is good for a year or two.

Regards,

? ?-Paul


On Mon, May 10, 2021 at 07:56 AM, <dkfcpalfd@...> wrote:
Paul:

Last night I cranked up TVC in G2.... up to 100.? Ran the GA, and I couldn't believe it, there was no backlash shown on the graph, in fact the actual plot was very close to and slightly left of the ideal curve.... I've never seen that before.? PHD2 told me I have no backlash, and no compensation is needed.? Amazing!!!

You were right, in that if I left TVC at 100 and tried guiding, the DEC guiding error was all over the place.? I cranked it down to 5 and it was still pretty rough, so I turned it down to 1 and that looked pretty good.

I also had been trying to calibrate a trial version of SkyGuard from Innovations Foresight.? Previously, I could not get it to calibrate, it was telling me it did not see enough movement on the Y axis.? That made me suspect DEC backlash.? So, with TVC set to 100.... it calibrated immediately, no problem.

At this point, I'm going to leave DEC Comp turned off in PHD2, and only apply TVC based on how my DEC guiding error appears.

I have only one more question:? Listen to the noise as I slew in DEC in the attached video file.? It only appeared after I started playing around with the DEC block bolts.? The noise seems to disappear if I loosen the wing bolts on the DEC block.? I thought I had it gone completely after installing the plastic shims, but it came back again last night.? I stopped the slew, loosened the wing bolts, and it disappeared.

My questions would be:? Is that noise indeed caused by improper adjustment of the bolts on the block?? Is the mount harmed potentially when that noise is happening?? What's the strategy for tightening those bolts?? I have the allen head bolts underneath backed out slightly, and use the wing bolts to tighten things up.? Too much torque on those wing bolts, and I hear that noise, or I get stalls.? Too little torque on the wing bolts, and I get noticeable play when rocking the scope back and forth by hand in DEC.? It seems like I have to have virtually no torque on the wing bolts..... stop turning when you feel it stop turning when tightening.? Is that OK?

Thanks so much.

Dan
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