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URGENT Focuser wiring help

drummerp

By drummerp
in DIY Astronomer

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drummerp

drummerp

Posted
Posted

Hi there,

I'm in the process of making an auto focuser but Im really struggling with the wiring. Can somone help me please.

help.bmp

I can connect the reostat from the battey to the motor and it works ok but I'm trying to use the toggle switch I bought. I'm wanting to use this switch to change the focus, in and out or the motor to turn left or right but I cant seam to work out the the right way to connect it all up.

Cheers

Neil

p.s - the toggle switch has 6 connector ends on it.

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Psychobilly

Psychobilly

Posted
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hang on had a better thought that one the speed would change as well as the direction... :)

[ATTACH]22351[/ATTACH]

add a push switch to adjust the focus... put it between the battery and the rheostat or the battrey will be draining all the time...

In my first sketch your changing the conenctions to the ends of the rehostat so the voltage at the wiper would change in "value" as well as polarity well unless you were bang in the middle... which wouldnt be good as if you were focussing slowly and overshot... when you reversed it it would suddenly be going faster

Peter...

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Psychobilly

Psychobilly

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Apologies for the daft mistake the first time...

That can be a bit of a problem...as the voltage you need to get the motor to turn the focuser will depend upon the "torque" required to drive it... tahts one of the reasons why stepper motors are better for use with focusers but a bit more complicated to drive...

I guess at one end of the rehostat the motor wont run? and you haven't got fine control as you turn it up?

What value Rehostat are you using?

Peter...

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Psychobilly

Psychobilly

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Lot more complicated to drive...

You Cant just repalce the normal motor with a stepper...

What mechanical setup are you using...

Are you using a geared motor? ok you'll lose fast focus speed but gain fine control...

There are some really usefull bits in a tescos value electric screw driver.. which costs less than a fiver and would be Rechargable... :)

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beamish

beamish

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Sorry I can't help re the last request, but I wish you luck in completing it successfully.

"There are some really usefull bits in a tescos value electric screw driver.. which costs less than a fiver and would be Rechargable.."

...........now that IS good to know- I do enjoy and appreciate these little insights Peter.:)

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Psychobilly

Psychobilly

Posted
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Yes(ish)

PWM drives pulse the motor with full voltage pulses and use varying on and off times to control the speed of the motor.. The net effect is similar to driving the motor at a lower voltage but you have the advantage of more torque...

They can be electrically noisy and can interfere with imaging devices...dependign on the drive frequency you may also hear an audible "hum" from the motor...

Blinky beat me to it :)

You could remove the preset from the pcb and replace it with a pot of the same value( make sure you get a linear one not a log one) and fit it to the box..

this might be stating the obvious but just in case...

the "focus" push switch can go in the input wiring side but the reversing "direction" switch must go into the output wiring side...

Peter...

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Psychobilly

Psychobilly

Posted
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The units available a bit cheaper form the manufacturer MFACOMO £9.79 + vat

I have used them for dew heater controllers in the past...(when i was to lazy to build my own) only thing you have to watch is if your doing a multi channel one you need to "float" the outputs can't common up the ground connections on the outputs them (at least with the previous design)...

Peter...

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themos

themos

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I don't think the stepper motors are tricky to operate, at least if you only want manual operation. If you want a computer to drive them then they can be a bit more of a faff, I guess, although Maplin do a L293D Stepper Motor Driver. I used a stepper from an old scanner, a home made flexible coupler and a bit of brass to attach the housing to an extra scope ring (it also carries the piggyback DSLR). The control I made myself out of a 12 way rotary switch, an on-off switch and a LED+resistor. 12 steps per revolution of the switch turned out to be just right for me given the existing gearing. It's great being able to nudge the focuser "digitally". The stepper can take anything from about 6 Volts to the full whack of the 12V powertank, you're only driving one coil at a time.

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Merlin66

Merlin66

Posted
Posted

A bit OT, but I built a selector/ speed controller handpaddle ( details on the web somewhere - MAPUG?) which allows me to switch between the #1206 and the #1209 (Zero Shift) focusers on my LX200.

You use the basic focuser to get close, switch over to the #1209 and drop the speed to "gently" pull it into focus. Been in use now for over two years without problems..

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drummerp

drummerp

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Hi Themos, if I was to purchase a L293D stepper motor drive ( L293D Stepper Motor Driver > Maplin )

how would I go about connecting this to the existing set up as above???

Cheers

Neil

I don't think the stepper motors are tricky to operate, at least if you only want manual operation. If you want a computer to drive them then they can be a bit more of a faff, I guess, although Maplin do a L293D Stepper Motor Driver. I used a stepper from an old scanner, a home made flexible coupler and a bit of brass to attach the housing to an extra scope ring (it also carries the piggyback DSLR). The control I made myself out of a 12 way rotary switch, an on-off switch and a LED+resistor. 12 steps per revolution of the switch turned out to be just right for me given the existing gearing. It's great being able to nudge the focuser "digitally". The stepper can take anything from about 6 Volts to the full whack of the 12V powertank, you're only driving one coil at a time.
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drummerp

drummerp

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I've just gone to Maplins that are open on sundays (suprised but glad) they didn't have any of the units mentioned above, all out of stock however the chap behind the counter assured me that this unit --- Panel Mounted Speed Regulator Module > Maplin would sort the speed issue out as long as I have 6 volts. So I've now hooked up a 6 volts battery pack from an old motor drive unit I had but I need some help in wiring the unit up.

I'm assuming I now no longer require the Reostat???

the speed regulator has 2 inputs and 2 outputs, how do I connect this up???

Many Thanks

Neil

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Merlin66

Merlin66

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Voltage Regulators from MFA Comodrills

It appears that there are two input wires ( positive/ negative -red / black) from the battery to the unit and two wire out to your DC motor ( again positive/ negative)

It works by interruping the output voltage to reduce the speed but hopefully not the torque. Very much like the PWC (pulse width control) used on dew heater bands.

You'll need a cross over reversing switch in the wire to the motor to give forward/ reverse.

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shaula

shaula

Posted
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apart from him making lots of grunting noises & cursing non-stop for the last two days - I think he might of done it!! just waiting for an unfurrowed brow.

No doubt that I'll benefit from this, so thanks guys.

Cheers

Claire

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drummerp

drummerp

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OK, I've finished all the wiring, I wont show you a picture of that as its a complete mess and I struggled squeezing it all into the box although, after you here what I connected upto it then your'll understand, loads of knobs.

I connected the Speed regulator also the rheostat, the POT aswell and the toggle switch, just look at the hand controller, funny isn't it.

Anyway, I got it running slow eventually but then when I tried to connect it to the scopes focuser it would'nt turn, the torque is really weak so any pressure on it just causes it to stop. :D

Therefore, I think I need to try and purchase another motor that has loads of torque and turns at a low RPM.

Oh yeah, you may wonder my I used a 6 volt battery pack its because the speed regulator wouldn't work without at least 6 volts.

Heres the pics of how it looks its cost me about £40 soo far and its still not working properly, at this rate I should have bought one off the shelf.....lol

post-16160-133877372875_thumb.jpg

post-16160-133877372883_thumb.jpg

post-16160-133877372892_thumb.jpg

post-16160-133877372898_thumb.jpg

Remember I've never done anything like this before so dont laugh too much please. :)

Cheers

Neil

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