SW Focuser upgrade PT 2

bmitchell82 (Brendan) · #1 10-09-2009, 05:44 PM

Well after looking on the net for something on how to make a simple cost effective/cheap electronic unit to do my focusing. (high power big telescope vibrations from doing focusing by hand can be very time consuming)

So this is what i have found so far!

RC servo motors
some cheap parts from Jaycar
=
Electronic focusing.

I am using a DPDT momentary switch for the backwards/forwards motion of the motor

and a Pentometer/Rheostat to increase/decrease voltage to the motor.

housed in a small box for ease of use.

Ill take some photos of the RC motor tonight and do a little bit of a show and tell on how i ripped the poor things guts out

then the pieces that im going to need and approximate costings on them. All in all it should be good enough and alot more presice than the sky watcher one avalible for 100 dollars.

So far i have spent 10 dollars on a HS-300 Hitec RC Servo and from tests proformed it will pull with ease 2kgs.
i think this should work

kinetic (Steve) · #2 10-09-2009, 06:04 PM

Brendan,

an RC servo is a great starting point for that BUT that's not how they work.

They need a pulse signal to work.
A basic servo has a PWM stream of pulses on the white control wire from memory and supply on the red and black.
By changing the duty cycle of the pwm you change the position of the servo.
Look up PWM RC servo circuit ideas on Google and you should find a few simple driver circuit ideas.

Steve

Quote:

Originally Posted by bmitchell82

and a Pentometer/Rheostat to increase/decrease voltage to the motor.

i think this should work

bmitchell82 (Brendan) · #3 10-09-2009, 06:30 PM

http://emediadesigns.com/focuser/# this is the main source of what i am using. from what i have read that im not actually using any of the circuitry within the servo motor, im only using the motor for its low speed high torque and the nice black plastic box it sits in.

the motor still only needs power or no power or inversed power (thats where the backwards and forwards motion comes in). when you pull the motor out it will only have a positive and negitive attachment to the PCB.

kinetic (Steve) · #4 10-09-2009, 06:35 PM

Ahh fair enough Brendan, I was assuming you were using the servo
as it comes...this site seems to just rip it open and use the motor and
gearbox minus electronics....Ignore what I said!

Good luck with it!

Edit: you beat me to it

Steve

bmitchell82 (Brendan) · #5 10-09-2009, 07:24 PM

Sall good mate

i had the same doubts for a start, i just missed the part where they rip everything out

RobF (Rob) · #6 10-09-2009, 07:56 PM

Looks intriguing Brendan. Be interested to see and hear how you go. Have never been able to justify the bucks for motorised focusing, but sure would be nice......

bmitchell82 (Brendan) · #7 10-09-2009, 08:05 PM

I guess i have just seen people that have it, and gee does it make life easier! at 15x digital zoom things arnt as stable and a little bump takes 10 seconds to get a clear reading because you don't know if its vibrations or if its atmospheric. plus when your doing solar work at 5x power mate. focus is that narrow its not funny.

.

Like i said ill post up what i have done and more than likely send in a set of schematics to put up on the projects if its all good.

bmitchell82 (Brendan) · #8 14-09-2009, 02:56 PM

alrighty then, went down to jaycar, and purchased a few things. the total cost so far is 28 dollars. all i have to do is a bit of testing on what the motor can do when attached to AA batteries and how many i need. once i have this then everything is set and ready to install into my hand paddle.

nearly there

bmitchell82 (Brendan) · #9 16-09-2009, 06:37 PM

okay peeps. all i have to do now is a bit o field testing! parts used

- HS-300 RC-servo motor modded for continuous rotation (easy)
- 1x 25 ohm rheostat (at a pinch a pentometer)
- 1 x dpdt switch
- 2 x 3.5mm head jacks + connectors to go into.
- a length of cable for connection from motor --> hand control
- 2 x AA battery holders
- box big enough to fit it all in.

Done

a bit of soldering and make yourself a bracket to suite your setup, I utilized printer belts (found inside a printer) and the cogs to go with it for the connection from the focuser --> motor. this also gives some reduction in torque required. currently im expecting ultra fine adjustment at maximum resistance and maximum speed at zero resistance. this set up should be good for 1.2kgs vertical lift. if it isnt then a bigger servo might be required.

total cost

$28.10 cents

time probably about 2hrs if i actually knew what i was doing