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Equipment Discussions >> Mounts

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Christopher Erickson
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Motor options for a barn door tracker new [Re: orlyandico]
      #5988006 - 07/24/13 03:40 PM

Quote:

I've looked at the ZX24r and I don't really see how it is simpler for the beginner than an Arduino..

sure it's Basic but the weird mangled C++ dialect used by Arduino is pretty simple, too.. and between a China Arduino Nano fur under $10 and a "special package" containing a ULN2003 chip and stepper motor with 1/64 gear reduction.. you're all set.




That's essentially true but most people have more experience with BASIC than with C or with Arduino, which was designed for "artists, musicians and other non-technical people."

With Arduino, I see a world where about one percent are talented programmers and everyone else struggles at just above the script-kiddie level, trying to modify and use code created by others.

If I were to tackle this project I would probably choose an ATmega328P chip and use WinAVR C to program it.

In fact I am tempted to whip out a circuit design and the support code and post it here, if there were any interest. I designed something similar for a college heliostat table derotator controller and the professors preferred that I do it in BASIC for them instead of Arduino. I could probably take that code and with a few simple code modifications, turn it into a barn door controller.

My advise is to use whatever you are comfortable with!


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sternenhimmel
super member


Reged: 06/06/13

Re: Motor options for a barn door tracker new [Re: Christopher Erickson]
      #5988109 - 07/24/13 04:50 PM

I think the Arduino is a good choice if people are interested in programming microcontrollers, but are intimidated by the learning curve associated with both the electronics and programming aspects. As they learn and write more complicated programs, they can delve further and branch out.

The arduino also serves as a development platform so that people can test ideas on the fly and see what would work and what wouldn't work. I don't have to move the chip from my programmer to the circuit each time I make a change.

In my final design, I'll probably end up with a PIC or ATmega driven circuit and move my Arduino to other projects under development.

On a stepper related note: Currently I'm half-stepping my motor, but would be interested in microstepping for smoother function. Can microstepping be easily implemented in software without any additional ICs?


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Christopher Erickson
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Motor options for a barn door tracker new [Re: sternenhimmel]
      #5988176 - 07/24/13 05:34 PM

Quote:

I think the Arduino is a good choice if people are interested in programming microcontrollers, but are intimidated by the learning curve associated with both the electronics and programming aspects. As they learn and write more complicated programs, they can delve further and branch out.

The arduino also serves as a development platform so that people can test ideas on the fly and see what would work and what wouldn't work. I don't have to move the chip from my programmer to the circuit each time I make a change.

In my final design, I'll probably end up with a PIC or ATmega driven circuit and move my Arduino to other projects under development.

On a stepper related note: Currently I'm half-stepping my motor, but would be interested in microstepping for smoother function. Can microstepping be easily implemented in software without any additional ICs?




If you are planning low-power, low heat and operating on minimal battery power, you really want to avoid half-stepping and microstepping. Shutting off the stepper holding current between steps will save you a significant amount of battery capacity versus keeping the coils energized to hold half or microsteps.

Personally I would suggest going with a gear reduction head on the stepper motor instead. Same end-result related to smooth driving without all of the wasted power and heat.

There are a lot of cheap ink jet printers out there that have bipolar steppers in them with worm drive gears and plastic worm wheels. Looking for junked printers in your area (or on eBay) could reward you with a good bipolar stepper worm drive assembly for almost nothing. You could post a wanted-ad on Craig's List too.

And yes, there are some good microstep driver chips out there but I have always avoided them in preference for gear reduction instead.

Gear reduction will give you a lot more torque and weight-handling capacity too.


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orlyandico
Postmaster
*****

Reged: 08/10/09

Loc: Singapore
Re: Motor options for a barn door tracker new [Re: Christopher Erickson]
      #5988646 - 07/24/13 10:38 PM

There really is no need to go looking through junky printers when you can get this for $3.20

http://www.ebay.com/bhp/stepper-motor-driver-board-uln2003

(and that's including shipping)

Actually the nice thing about an Arduino is if you buy an Uno (with the DIP28 packaged Atmega328, not the SMD package) you can pull out the Atmega328, wire it up to a super-minimal circuit (2 small caps, 1 bypass cap, and a crystal) and it will still work.

http://www.instructables.com/id/Standalone-Arduino-ATMega-chip-on-breadboard/

"Arduino" is nothing more than a tiny bootloader for the AVR, and a nice IDE that hides the ugliness of AVRdude and the cross-compiler.

Here's another wrinkle.. the good folks at Digilent have come up with a new board, the DP32. It is not physically compatible with Arduino, but it is software-compatible and uses the MPIDE (Arduino-compatible) IDE from Digilent.

The nice thing? the DP32 uses a PICMX that is also a DIP28 and can also be put in a minimal circuit like the Atmega328. The difference? 50 MHz, 512K of flash, and 32K of RAM - enough to implement a full-blown telescope controller with GoTo. If you want to go there..


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Christopher Erickson
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Motor options for a barn door tracker new [Re: orlyandico]
      #5988748 - 07/24/13 11:51 PM

Quote:

There really is no need to go looking through junky printers when you can get this for $3.20

http://www.ebay.com/bhp/stepper-motor-driver-board-uln2003

(and that's including shipping)

Actually the nice thing about an Arduino is if you buy an Uno (with the DIP28 packaged Atmega328, not the SMD package) you can pull out the Atmega328, wire it up to a super-minimal circuit (2 small caps, 1 bypass cap, and a crystal) and it will still work.

http://www.instructables.com/id/Standalone-Arduino-ATMega-chip-on-breadboard/

"Arduino" is nothing more than a tiny bootloader for the AVR, and a nice IDE that hides the ugliness of AVRdude and the cross-compiler.

Here's another wrinkle.. the good folks at Digilent have come up with a new board, the DP32. It is not physically compatible with Arduino, but it is software-compatible and uses the MPIDE (Arduino-compatible) IDE from Digilent.

The nice thing? the DP32 uses a PICMX that is also a DIP28 and can also be put in a minimal circuit like the Atmega328. The difference? 50 MHz, 512K of flash, and 32K of RAM - enough to implement a full-blown telescope controller with GoTo. If you want to go there..




That $3.20 item isn't a gearhead stepper or a worm drive stepper and that was the whole-reason to look at some discarded inkjet printers.

Arduino is fine if that is what someone wants to use. However over the years I have seen a lot of ardent campaigning for various microcontrollers and program languages by people that have never actually rolled any code or built anything functional. Present company excepted, of course!

Clear skies and chocolate...


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sternenhimmel
super member


Reged: 06/06/13

Re: Motor options for a barn door tracker new [Re: Christopher Erickson]
      #5988755 - 07/24/13 11:57 PM

Good advice. I implemented a 10ms on/ 65ms off full-stepping. This brings the current consumption for the motor down to < 100 mA. I'm also using a 2000 mAh 7.4V LP-E5 rechargeable battery for now and am driving the arduino off a 9V since it only pulls 30-50mA.

I've already got a 4 to 1 gearing on the stepper, and the stepper is 200 steps/rotation. With full-stepping that gives me 1.8 degrees/step, and with gearing, that's 0.45 degrees/step. My rod is 1/4"-20, so something like 0.006 mm/step which is something like 0.00122 degrees/min (for a 28.8cm arm). I imagine that is more than accurate enough for my purposes.

The bigger question now is whether the motor vibrations will be an issue, and if I can even polar align accurately enough to make stepper accuracy matter.

Clear skies the next few nights

Edited by sternenhimmel (07/25/13 12:06 AM)


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orlyandico
Postmaster
*****

Reged: 08/10/09

Loc: Singapore
Re: Motor options for a barn door tracker new [Re: sternenhimmel]
      #5989006 - 07/25/13 05:32 AM

Chris, the stepper motor in that link has a 1/64 gear head and is unipolar with 48 ppr. I have like 10 of them. The only downside is that since they aren't hybrid steppers, they can only do about 200pps maximum - you're not going to be slewing anywhere with these motors.. But for tracking they are fine.

So $3.20 with shipping for both the gear head stepper and the ULN2003 board can't be beat.

Also.. I am not an embedded developer. But I have several different embedded boards to play with. The strength of Arduino is the huge community and the very fine libraries.

Check out Mike McCauley's AccelStepper. Its a wonderful piece of code. While it is true that the Arduino forums are littered with newbies writing spaghetti code, there's also a lot of wisdom there. It does get annoying when I go ask a question and get responses meant for newbies. Maybe part of the disdain (?) of traditional developers for Arduino is because it makes embedded programming so approachable that every rasta hippie is doing it?

But overall I think the Arduino experience is a very positive one.

And I would not go back to the days of HC11s and uploading HEX files over a serial line. Arduino still does that... But all the complexity is hidden.


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Christopher Erickson
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Motor options for a barn door tracker new [Re: orlyandico]
      #5989009 - 07/25/13 05:38 AM

Quote:

Chris, the stepper motor in that link has a 1/64 gear head and is unipolar with 48 ppr. I have like 10 of them.

So $3.20 with shipping for both the gear head stepper and the ULN2003 board can't be beat.




I guess I missed that in the specs so that isn't too bad.

Personally I would still prefer a worm gear reduction instead of spur gears. Worms can't be overrun by force on the output shaft.


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orlyandico
Postmaster
*****

Reged: 08/10/09

Loc: Singapore
Re: Motor options for a barn door tracker new [Re: Christopher Erickson]
      #5989017 - 07/25/13 05:45 AM

I don't think there are any worm drive gear head steppers... All I've seen are spur and planetary gearheads.

And the cheap steppers are all tin can. You want hybrid (for decent slewing speed) and you're talking big bucks.

The Vexta Pk243's with 10:1 gearheads I'm using on my AP600 GoTo conversion are $250 a pop new. Good thing there's eBay...


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Christopher Erickson
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Motor options for a barn door tracker new [Re: orlyandico]
      #5989569 - 07/25/13 01:31 PM Attachment (19 downloads)

From a $5 junk inkjet printer.

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sternenhimmel
super member


Reged: 06/06/13

Re: Motor options for a barn door tracker new [Re: Christopher Erickson]
      #5989905 - 07/25/13 04:30 PM

I've gotten some decent steppers from ink jet printers. The reason I didn't use any of them personally was because they had small shafts and were only 50 steps/revolution. I was willing to put out the extra few bucks to just buy something new that fit my design requirements. If I had the right tools, I could have made do with what I had.

However, I totally support and practice the philosophy of harvesting components from old hardware. I especially recommend de-soldering goodies from circuit boards.

Edited by sternenhimmel (07/25/13 04:32 PM)


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Groo
member


Reged: 03/05/09

Loc: Calgary, AB Canada
Re: Motor options for a barn door tracker new [Re: orlyandico]
      #6139365 - 10/15/13 04:04 PM

Quote:

one huge advantage of using a stepper motor and micro-controller, is that you can get away without a bent shaft.

with a straight shaft the speed has to be varied as you go along the shaft (this is what the Astrotrac does). So in your shoes, I'd use an Arduino, an A4988 Pololu stepper motor controller, the AccelStepper library, and one of those steppers (you could micro-step them to smooth them out, but frankly at 400 steps/rev it will not be an issue).

You can also do guiding and periodic error correction with the Arduino...




Are you able to tell me what rate I would need to increase the rotation speed with the Arduino if using a straight rod?


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Christopher Erickson
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Motor options for a barn door tracker new [Re: Groo]
      #6139392 - 10/15/13 04:21 PM

Quote:

Quote:

one huge advantage of using a stepper motor and micro-controller, is that you can get away without a bent shaft.

with a straight shaft the speed has to be varied as you go along the shaft (this is what the Astrotrac does). So in your shoes, I'd use an Arduino, an A4988 Pololu stepper motor controller, the AccelStepper library, and one of those steppers (you could micro-step them to smooth them out, but frankly at 400 steps/rev it will not be an issue).

You can also do guiding and periodic error correction with the Arduino...




Are you able to tell me what rate I would need to increase the rotation speed with the Arduino if using a straight rod?




It would be a mathematical function that would vary the speed based on the current angle of the screw to the axis. The speed would be different when the wedge was mostly-closed versus mostly-open. The radius of the wedge, thread pitch of the drive screw and ratio of the motor drive and gearing would all be inputs into that mathematical function.

A curved screw allows the drive speed to be constant regardless of the position of the wedge and makes everything else simpler to deal with.


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Phil Sherman
Pooh-Bah


Reged: 12/07/10

Loc: Cleveland, Ohio
Re: Motor options for a barn door tracker new [Re: Christopher Erickson]
      #6140481 - 10/16/13 09:17 AM

An alternative to a curved screw is a curved pillar block on the fixed side of the barn door. The radius of curvature needs to be the same as the distance from the hinge to the (closed door) contact point of the screw. Now, as the hinge opens, the screw will push against the pillar block whose contact surface is always the same distance from the hinge.

The downside of this approach is that the length of time that you can track is controlled by the size of the pillar block. A hole cut in the moving portion of the barn door for the pillar block will allow you to start with the door completely closed.

Phil


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Groo
member


Reged: 03/05/09

Loc: Calgary, AB Canada
Re: Motor options for a barn door tracker new [Re: Phil Sherman]
      #6140728 - 10/16/13 11:40 AM

if I make a form/template to curve the threaded bolt, the curve of the template needs to match the center of the bolt correct not the inside or outside?

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Phil Sherman
Pooh-Bah


Reged: 12/07/10

Loc: Cleveland, Ohio
Re: Motor options for a barn door tracker [Re: Groo]
      #6142642 - 10/17/13 10:38 AM

The center of the bolt needs to be the correct distance from the hinge. The bending form needs to be sized to match the inside edge of the bolt, 1/8" smaller than the hinge to bolt dimension if you're using a 1/4" bolt.

Unfortunately, that form won't work. A steel bolt is an elastic material (when being bent) and if you bend it against a form that size, you'll end up with a bolt with a larger radius of curvature. You'll need to use a smaller form to bend it or significantly heat the rod while it's held against the form to relieve stress and have it keep the shape you want.

Phil


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