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Tim C
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Reged: 11/11/07

Loc: Marietta, GA
Help needed: Motor speed control for barn door
      #5685749 - 02/17/13 06:59 PM

Hi all,

My next project is going to be a barn door tracker fashioned after the Gary Seronik version (maybe invented by Ed Jones?). Anyway, my first step was to order a motor off of ebay for $19. The model I ordered runs at 6 rpm @ 12 volts. I know I'll need some spur gears to get the bolt turning at 1 RPM but was going to first figure out what motor RPM I would be starting with which will be be function of the voltage I'm delivering to the motor. If I use the same gears that Gary did in his article, I'll need about 8 volts to get the motor to turn at 4 rpm. I was thinking of using a 9 volt battery (or perhaps multiple AA's to get to 12 volts) and using a motor control circuit/box to get it to the precise rate.

I can follow the design on Gary's site (although I don't really understand how it all works) but got to wondering if there is an off the shelf motor control solution (perhaps cheaper) that I could use to regulate the motor to 4 rpm (or another lower rpm for that matter)?

Any advice on this question would be much appreciated. I don't mind doing some soldering (probably fun) but an off the shelf solution would be easier. I found a number of listings for pulse width modulated motor controls but they all seem to require 12 volts to 40 volts DC. Does that mean I'd have to supply at least 12 volts and then how do I know if the unit has the "range" to get it down to ~8 volts needed to spin the motor at 4 rpm?

You can tell I have foggy notions of what is required but am a little lost so again any help is appreciated.

Tim


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Tim C
Pooh-Bah
*****

Reged: 11/11/07

Loc: Marietta, GA
Re: Help needed: Motor speed control for barn door new [Re: Tim C]
      #5685870 - 02/17/13 08:10 PM

I found this - looks like a very inexpensive solution:

http://www.bakatronics.com/shop/item.aspx?itemid=383


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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: Help needed: Motor speed control for barn door new [Re: Tim C]
      #5685940 - 02/17/13 08:52 PM

Yep, that looks like a workable bit of gear for your project.

Forget about the 9v battery. It won't do the job. A 12v assembly using AAs will work but D cells or even a small 12v gel cell would be much better.

dan


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Tim C
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Reged: 11/11/07

Loc: Marietta, GA
Re: Help needed: Motor speed control for barn door new [Re: dan_h]
      #5686520 - 02/18/13 07:45 AM

Thanks Dan. I ordered the kit at the link. Never fails, right after I ask the question I find what I'm looking for. I will play with some different battery combos but I'm thinking you are probably right about going with 12 volts.

Tim


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GlennLeDrew
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Help needed: Motor speed control for barn door new [Re: Tim C]
      #5687108 - 02/18/13 03:09 PM

When faced with difficulty in achieving a specific rotation rate, one can design for a longer or shorter hinge-to-drive rod distance. There is no reason to be hidebound to 1 RPM.

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Tim C
Pooh-Bah
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Reged: 11/11/07

Loc: Marietta, GA
Re: Help needed: Motor speed control for barn door new [Re: GlennLeDrew]
      #5687173 - 02/18/13 03:41 PM

True - one reason I started with the motor and control first so I know what ive got in terms of rpm. I can then design the tracker around that if for some reason I can't match the Gary Seronik plan exactly.

Quote:

When faced with difficulty in achieving a specific rotation rate, one can design for a longer or shorter hinge-to-drive rod distance. There is no reason to be hidebound to 1 RPM.




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Geo.
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Reged: 10/01/08

Loc: Upstate NY
Re: Help needed: Motor speed control for barn door new [Re: Tim C]
      #5691084 - 02/20/13 02:55 PM Attachment (13 downloads)

The kit is based on a fairly common 555 timer circuit.

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HKang
member
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Reged: 06/14/10

Re: Help needed: Motor speed control for barn door new [Re: Geo.]
      #5691385 - 02/20/13 05:33 PM

555 DC motor control does not give constant speed over different load.

Try 555 pulse generation + stepper motor. You will get much better speed control. Only limit is temperature dependence of 555.
http://www.ebay.com/itm/290758877302?ssPageName=STRK:MEWAX:IT&_trksid=p39...
Stepper motor and controller cost only $8.


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wirenut
Pooh-Bah


Reged: 09/21/06

Loc: m'dale Pa
Re: Help needed: Motor speed control for barn door new [Re: HKang]
      #5691778 - 02/20/13 09:25 PM

I use this LM317 voltage regulator and a 2 pole double throw switch(for reverse)to control the 12V motor on my EQ platform. it's off the self just plug and play and has AC/DC input. I was concerned a PWM would induce vibrations, they say they don't but I wanted to be safe. I made cables to hook up a battery from old cordless drill(18V)instead of buying batteries. I also scavenged a plugin 12v ac transformer if I ever need it.

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Geo.
Carpal Tunnel
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Reged: 10/01/08

Loc: Upstate NY
Re: Help needed: Motor speed control for barn door new [Re: HKang]
      #5692846 - 02/21/13 02:11 PM

Quote:

555 DC motor control does not give constant speed over different load.




This why op amp control is better. ICs like the LM339 are stable at different temperatures. Some neat ideas here: http://solartracker.greenwatts.info/mini_tracker.htm


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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: Help needed: Motor speed control for barn door new [Re: HKang]
      #5692890 - 02/21/13 02:45 PM

Quote:

555 DC motor control does not give constant speed over different load.

Try 555 pulse generation + stepper motor. You will get much better speed control. Only limit is temperature dependence of 555.
http://www.ebay.com/itm/290758877302?ssPageName=STRK:MEWAX:IT&_trksid=p39...
Stepper motor and controller cost only $8.




This kit does not have the stepper controller. What is included is the motor and driver amplifier. You still need the clock and phasing generator portions of the stepper controller.

dan


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Geo.
Carpal Tunnel
*****

Reged: 10/01/08

Loc: Upstate NY
Re: Help needed: Motor speed control for barn door new [Re: dan_h]
      #5694415 - 02/22/13 10:42 AM Attachment (6 downloads)

I think we are getting all too complex a system here. Can't see much point in having to drag out a PC to control a barn door tracker. Take a look at the "Celestron Astromaster drive motor modifications" from Sept. for a simple DC motor controller that's surely accurate enough for this project.

Yes, the ULN2002 is a fairly sophisticated Darlington array, but not a stepper driver. But even something like the L298 driver needs external imputs.


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Ed Jones
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Reged: 04/06/04

Loc: Sin-sin-atti
Re: Help needed: Motor speed control for barn door new [Re: Geo.]
      #5694635 - 02/22/13 12:41 PM

Yes a timing motor is simpler to drive, cheaper and constant rate.

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Tim C
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Reged: 11/11/07

Loc: Marietta, GA
Re: Help needed: Motor speed control for barn door new [Re: Ed Jones]
      #5694939 - 02/22/13 03:08 PM

I didn't look extremely hard but it seemed like most of the timing motors that I found needed A/C which I didn't want to fool with.

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Jeff Phinney
super member


Reged: 02/20/13

Loc: CA
Re: Help needed: Motor speed control for barn door new [Re: Tim C]
      #5695803 - 02/22/13 10:43 PM

Not sure what the fear/problem is with using an AC timing motor. They've been used for years for purposes just like this and they sure makes things much much easier.

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Tim C
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Reged: 11/11/07

Loc: Marietta, GA
Re: Help needed: Motor speed control for barn door new [Re: Jeff Phinney]
      #5696186 - 02/23/13 08:50 AM

cause you can't plug it into a cactus I know there are gadgets used to convert to a/c but that adds to complication so in the end it's all about a wash... motor control with dc or bring some contraption to convert dc to a/c. Just depends on where you're planning to use it as far as what is best.

Quote:

Not sure what the fear/problem is with using an AC timing motor. They've been used for years for purposes just like this and they sure makes things much much easier.




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Tim C
Pooh-Bah
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Reged: 11/11/07

Loc: Marietta, GA
Re: Help needed: Motor speed control for barn door new [Re: Tim C]
      #5696309 - 02/23/13 10:35 AM

Well, I soldered together the motor control circuit and seems to work fine. It has a dc output range of about 6.5 volts to 12.7 when hooked up to a 12 volt power source. I can get the motor turning at about 4 rpm right around 8 volts of output. The cheap little ebay motor is a noisy sucker though. Might have to build a little box around it on the tracker to muffle it a bit.

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