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Lakeside focusers backlash


TerryMcK
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My scopes all have Lakeside focusers with the exception of the RedCat which currently is manual only. That will be upgraded to a DeepSkyDad focuser soon.

While we have been having this spell of cloudy weather I decided to measure each scopes tube movement with their focusers engaged.

To do this I lashed up a digital dial test indicator to the fixed part of the scope and placed the plunger/contact point against the rear of the camera.

Then through software wound the scope tube in a bit to take up the backlash. Resetting the dial indicator to zero I then commanded the tube outwards 1 tick at a time, counting the number of ticks it took for the backlash to be taken up and the scope tube to start moving. I repeated this a number of time to ensure I got an average value.

 

The results were quite astonishing. The two scopes I concentrated on were the WO ZS103 and WOZS73.

It took 23 ticks for the ZS103 to start moving and 85 for the ZS73 to start moving. I know that the focusing mechanisms on each scope can be adjusted to make the pinion engage into the rack more but on closer examination the backlash was being produced by each of the Lakeside motors themselves. This is to be expected as they are electro/mechanical devices.

 

Anyway the capture software I use, EKOS, has a setting where the number of backlash ticks can be entered and it then takes care of focusing. Each scope has a different profile so 23 is saved with the ZS103 and 85 for the ZS73 so I don't have to worry about it again.

 

I'm sure other capture software has similar backlash fields that can have your own values inputted.

 

The whole point of the exercise was to measure the physical backlash present rather than guessing and was successful. I will also measure the RedCat/DeepSkyDad combo when I get the DSD focuser.

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2 hours ago, TerryMcK said:

My scopes all have Lakeside focusers with the exception of the RedCat which currently is manual only. That will be upgraded to a DeepSkyDad focuser soon.

While we have been having this spell of cloudy weather I decided to measure each scopes tube movement with their focusers engaged.

To do this I lashed up a digital dial test indicator to the fixed part of the scope and placed the plunger/contact point against the rear of the camera.

Then through software wound the scope tube in a bit to take up the backlash. Resetting the dial indicator to zero I then commanded the tube outwards 1 tick at a time, counting the number of ticks it took for the backlash to be taken up and the scope tube to start moving. I repeated this a number of time to ensure I got an average value.

 

The results were quite astonishing. The two scopes I concentrated on were the WO ZS103 and WOZS73.

It took 23 ticks for the ZS103 to start moving and 85 for the ZS73 to start moving. I know that the focusing mechanisms on each scope can be adjusted to make the pinion engage into the rack more but on closer examination the backlash was being produced by each of the Lakeside motors themselves. This is to be expected as they are electro/mechanical devices.

 

Anyway the capture software I use, EKOS, has a setting where the number of backlash ticks can be entered and it then takes care of focusing. Each scope has a different profile so 23 is saved with the ZS103 and 85 for the ZS73 so I don't have to worry about it again.

 

I'm sure other capture software has similar backlash fields that can have your own values inputted.

 

The whole point of the exercise was to measure the physical backlash present rather than guessing and was successful. I will also measure the RedCat/DeepSkyDad combo when I get the DSD focuser.

I amazed that one focuser has nearly 4 times the amount of backlash than the other. Obviously tolerances have quite a wide margin in the Lakeside focusers, and no doubt my ZWO focusers are the same.

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Yes I thought it wasn't very much as once the drawtube started to move it took 3 ticks to move the digital display from 0.01mm to 0.02mm which is just over a third of a thou 0.00039" in old money. 

That reminds me of my very early engineering days 40 odd years ago Mark. We used to use Rizla's and spit stuck to the face of a workpiece when milling. When you manually inched the cutter towards the paper and when it flew off you knew you were a thou and a half from the workpiece. Eeee you try telling young uns that nowadays and they wouldn't believe you (comes out of Monty Python 4 Yorkshiremen mode).

 

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I was having issues with my Lakeside/Ekos hunting round, had to play around with the settings and I think I ended up leaving backlash set to 300. Last few sessions were fine.

Always worth rounding up the measured backlash figure.

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