Remote electronic focus for telescope (DIY remote follow focus)--- make money online

I just finished this telescope remote

focus control so I'll first give me a

demonstration of how it works when I

turn the knob on this control box the

focus wheel on the telescope is turned

in just about a one-to-one control so

the whole point of this is so that you

don't actually have to touch the

telescope while focusing it even the

slight even with a steady hand very

slight vibrations will jiggle the image

and while the image is bouncing around

it's difficult to focus so the idea with

this is that you can turn the knob and

not touch the telescope at all and get a

really precise focus so I'll show you

how its put together the original focus

knob for the telescope was this hollow

rubber knob and it slipped over the end

of this metal tube sticking out of the

back of the telescope so at first I

thought well the best thing to do is

just beat a couple of motor shaft to

this shaft can be able to be able to put

the motor shaft inside but as it turns

out that's not going to work because

inside this shaft there's a lead screw

which actually moves the mirror inside

the telescope so you can't put anything

in here because when you focus it all

the way out the lead screw actually

backs all the way out the end of this

shaft which is why this knob is hollow

too so to get around that problem I

thought the next best thing would be to

put a ACOG hub sprocket on there and

this would be Hollow and also get the

motor out of the way so that's what I

did so this is am made for a toothed

belt part that I got from McMaster and I

machines the the original aluminum boss

out of the middle and made a plastic

boss that will fit the outside diameter

of the focus wheel and then I got a

toothed belt and made this bracket for a

stepper motor and in another sprocket

for the stepper motor so then I can

pivot the motor down and get a little

bit of tension you really don't need too

much tension for these belts they

actually track quite well it's just a

little tiny bit of tension

so there's that you can see that it

operates really smoothly there's very

little slippage in the whole Sydney

whole mechanical system the stepper

motor is a unipolar four coil motor it

actually has eight wires coming off of

it with two Commons so I just joined the

Commons together and then you have four

phases to worry about and I used a just

a db9 connector so that I can just

disconnect this thing quickly not have

something heavy hanging off the

telescope I only used five of the wires

so there's just one common with the four

phases and the motor I think is rated

for 24 volts DC and seven and a half

degrees per step it's actually not very

powerful if I turn the knob quickly on

the control it will slip steps but just

turn the knob slowly and it doesn't

really matter the only input to this

circuit is this quadrature encoder which

is just has the knob on the other side

of the box and on the top of the box

there and this is a not an optical

quadrature encoder it's actually a

physical electrical quadrature encoder

and the two phases a and B come off and

go into this Avago chip a quadrature

decoder and the decoder is a an up/down

counter that's triggered by the the knob

rotations so for every state transition

generated in this mechanical quadrature

encoder the counter in that Avago chip

counts up or down one click I have it

set right now to 1x decoding so it

actually takes an entire transition I

guess an entire up and then down on one

of the phases for it to actually count

up or down you can also configure this

chip to count 2x or 4x so that the

counter will change for every single

state transition but I found that it was

actually too quick and I didn't need

that much speed I was actually more

interested in accuracy

so for one turn of the knob I think you

get about one turn of about put the way

I have this set up now so the up/down

counting out of this Avago chip triggers

this ELab digital stepper motor control

I see I really could have done this with

a lot of other things even discrete

logic components but I had this chip

laying around in my box and I wanted to

use it so this thing just keeps track of

the phase the correct phases for the

stepper motor so all you have to do is

tell this thing up or down and it will

keep track of the phases of the stepper

motor and it just handles that bit and

then for the actual motor driving I just

have little NPN transistors probably 20

to 22 s to actually handle the the

winding voltage and this chip is just a

5:58 timer which provides a clock signal

for the Avago but the clock is really

not important all it's there for is to

give the chip something to trigger on

but the speed of the clock doesn't

matter it doesn't even matter if it

drifts a lot especially for this

application since this is a very very

low speed application so I was totally

wrong about the one to one control ratio

it actually turns out that one turn is

only about a quarter of the actual focus

range and so you know it's to pretend

this is like straight up and down with

this knob here okay so if I if I slowly

turn the control knob all the way around

once we've really really got about a

quarter rotation felt like that so

that's fine I mean it like you say when

you get down to using this remote focus

control it's really for very fine

adjustments one thing I've noticed is

that it doesn't switch directions

particularly well so it it tracks very

smoothly if you stand in one direction

it's really quite nice and smooth you

can even you can see the actual steps of

the motor going by there and that's

that's definitely fine enough for focus

control on this telescope

but when you start going back and forth

sometimes the behavior is not quite so

good all it does can be tracking pretty

nicely now anyway I get to try this out

on an actual telescope viewing night so

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