Focuser Modification help

[Astroman (Andrew Wall)]

Hello,

Has anyone modified a standard focuser so it has slow motion control? I do have a motor on it but I am finding that it is still too course in movement. I would like to have at least a 10:1 gear reduction.. Does anyone have any info?

[alistairsam]

Hi andrew
Which focuser is this?
Are you using a stepper motor?

[Shark Bait (Stu)]

Interesting thread.

I was considering buying an electronic kit and making up my own controller for the standard SW flex-tube dob focuser.

How sensitive does a stepper motor need to be to achieve the desired result?

[Astroman (Andrew Wall)]

The focuser is from Scopestuff http://www.scopestuff.com/ss_frc5_L.jpg I am using a 12v-24v DC Motor speed controller with a 12v motor.

[Shark Bait (Stu)]

What are the specs on the motor that you are using at the moment?

Are the following items from Jaycar going to be sensitive enough to allow slow motion control on standard focusers?

Sounds like a nice little project if the parts are up to the task.


12VDC 48 Step / 7.5° Stepper Motor

• Standard 48 step / 7.5° design.
• Flange mount 3.0mm hardened steel shaft.

Specifications:
• Rated voltage: 12VDC
• Rated current: 1.1A/phase
• Phases: 4
• Steps per revolution: 48
• Stepping angle: 7.5°
• Drive method: Unipolar chopper drive
• Resistance per winding: 20 ohms
• Starting frequency: 600pps (max)
• Holding torque: 700g/cm
http://www.jaycar.com.au/products_up...duct_13543.jpg


10A 12VDC Motor Speed Controller Kit


Refer: Silicon Chip June, 1997
Use this kit for controlling 12V DC motors in cars such as fuel injection pumps, water/air intercoolers and water injection on performance cars. You can also use it for headlight dimming and for running 12V DC motors in 24V vehicles. The circuit incorporates a soft start feature, which is used to reduce inrush currents, particularly if the kit is to control 12V incandescent lamps. As presented, the kit will control
loads up to 10 amps, although the addition of an extra MOSFET transistor will double that capacity to an amazing 20 amps.
* Kit includes PCB plus all electronic components to build the 10A version.
* Extra MOSFET available separately, ZT2450.
http://www.jaycar.com.au/products_up...oduct_5720.jpg

[Astroman (Andrew Wall)]

The DC motor speed controller wont run the stepper motor? I do have a gear reduction on the motor, but I was thinking something like a 10:1 knob on the focuser so I can drive that with the motor... Anything like that available?

[Shark Bait (Stu)]

Some of the members from BAS use these types of focuser controllers. At the next gathering I will ask around and see what they are doing.

I don't know enough about it at the moment but I know they are using their gear successfully to take astro images at the dark sky weekends.

[ZeroID (Brent)]

As I have found out you need to be able to make extremely small focusser movements. I bought a 10:1 focusser in the end after trying to design and make several reduction drive systems for my original 1:1 focusser.
I beleive there are motor drive kits for 10:1 using stepper motors which are needed to acheive accuracy and repeatabilty in focussing.

[Karls48 (Karl)]

Have look on this site.
http://bedair.org/Focus/focusproject.html
I had build one for RP focuser and it works fine.

[2stroke (Jay)]

I'am thinking of a cheap dc geared motor off ebay and a pwm controller for the RP on the newt. You can get these motors for bugger all and in a ton of different ratio configurations, though for the price backlash maybe an issue lol. http://www.ebay.com.au/itm/37mm-12V-...item415cb825f9 if you cant get a good focus with that and a pwm then your pretty much in trouble, only wind out times a issue though for a crayford you could just loosen side and lock down then adjust.

[RAJAH235]

I used an old, burnt out, servo, from a 2 channel radio.
I removed the PC board & I modified the gearbox to do 360 Degs rotation & made a small Al. pulley.
A simple "O" ring for the drive belt & a small, 2 x AA powered, Up/Centre off/Down switch & a pot for speed control through a simple voltage/current regulator.
I also included an on/off switch to conserve the batteries.
All up cost of about $10.00.

> http://www.iceinspace.com.au/forum/a...owse.php?a=552

[astro_nutt]

At the moment I have modified my standard R+P by attaching a lid from a jar of peanut butter to one of the focuser knobs and practice being delicate in turning it!

[Astroman (Andrew Wall)]

Originally Posted by Karls48

Have look on this site.
http://bedair.org/Focus/focusproject.html
I had build one for RP focuser and it works fine.

Thats the sort of thing I was after, thanks..

[Astroman (Andrew Wall)]

Originally Posted by RAJAH235

I used an old, burnt out, servo, from a 2 channel radio.
I removed the PC board & I modified the gearbox to do 360 Degs rotation & made a small Al. pulley.
A simple "O" ring for the drive belt & a small, 2 x AA powered, Up/Centre off/Down switch & a pot for speed control through a simple voltage/current regulator.
I also included an on/off switch to conserve the batteries.
All up cost of about $10.00.

> http://www.iceinspace.com.au/forum/a...owse.php?a=552

I have made one of these before also. Was after something a little different, like the 10:1 reduction knobs on the newer focusers... I have plenty of servo's laying around, being an aeromodeller you collect stuff like that