Is +/- 0.1 degree accurate enough for a digital setting circle

[Demo johnny]

http://www.machine-dro.co.uk/rotary-ang ... haft-.html

I found this, its by wixey. Cutting a hole in the top piece of the base enough for a wheel to be driven by the bottom to then turn the rotary encoder this gives a digital setting circle setup for under £50 or £70 for a complete setup if you get the inclinometer.

Am I missing something, whats the catch?

[Demo johnny]

http://www.machine-dro.co.uk/rotary-angle-encoder-and-remote-display-with-a-6mm-diameter-shaft-.html

here is the link.

0.1 degree is the same as sky commander

can't work out the resolution of the encoder on this unit but at the price point saving it has to be worth a punt?

[Steve Ward]

I'd have thought it was more than accurate enough for a dob , bearing in mind that by the time you've checked the readout on the inclinometer and the readout on the circle encoder display you can pretty much guarantee that the view in the eyepiece will have moved by about 0.1 degree ! !

Steve.

[knobby]

Its pretty accurate... Bit of a pain to fit though

[knobby]

Have a skim through this thread...

[IanL]

Sounds like a fun project.

Not a Dob user so may be completely off target here, but looking at the encoder/readout you have linked to, it seems to me that all it allows is to set the zero degrees position at the current angle of the shaft, and then measure the shaft rotation in degrees, with one complete rotation of the shaft equalling 360 degrees. If I read your suggesting for fixing it/driving the shaft correctly, you want to:

- Attach a wheel of some sort to the shaft.

- Cut a slot in the upper base.

- Attach the encoder so the wheel goes through the slot and is driven by friction on the fixed lower base as you rotate the scope and upper base?

Due to the design of the encoder/readout, one complete rotation of the dob needs to result in one rotation of the encoder's shaft; i.e. you would want the diameter of the wheel and the diameter of the circumference travelled by the wheel to be the same to give a 1:1 ratio. This assumes no slippage of the wheel as it goes round.

To eliminate any possibility of slippage, you'd need to attach the encoder shaft vertically to the (presumably fixed) bolt at the centre of the base, and the encoder body to the base itself; centering could be problematic here - you'd need some kind of drive shaft extension attached to the dead centre of the pivot bolt (?) Centering the encoder shaft would be less of an issue as you could use a beam coupler to deal with any slight misalignment:

http://www.sourcingmap.com/17mm-diameter-22mm-length-6mm-encode-beam-coupling-coupler-p-214908.html?currency=GBP&utm_source=google&utm_medium=froogle&utm_campaign=ukfroogle

Or maybe use a pair of same sized gears, one on the pivot and one the encoder shaft which could sit off to the side of the base, plus a toothed drive belt, which would eliminate any slippage issues. (No idea if either of those approaches would be practical options).

I guess the driven wheel approach is more in keeping with the 'simple is better' philosophy of dob mounts though, and resetting to zero in case of problems would be an awful lot quicker than recovering with a crash/power problem with a computerised EQ mount (usually waste the first hour of any session debugging which bit of USB-connected technology is not playing ball this time!)

[Joseki]

ive been thinking about doing this mod to my diy mount. mines built with a lazy susan from the start so the centre is empty at the mo. If I do go with the digital angle measurer I'll be able to mount the encoder directly without much hassle I reckon.

[knobby]

My first attempt... Worked but too much play.

Its now straight on top of centre bolt, much better. I'll post some pics later

[knobby]

Have a skim through this thread...

Edit missing link

http://stargazerslounge.com/index.php?/topic/155345-Dob-eqautorial-rotary-encoder-vs-Setting-circles