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Messages - pterodyne

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61
DIY AstroEQ / Re: Losmandy Titan stepper conversion
« on: April 17, 2015, 04:56:25 »
Tom,

You mention earlier in this thread that the max Vref*2 for setting the current is .72V which puts us at 1.44A.  The reason you cite is the reverse polarity diode on the AstroEq board.  Assuming I never plug in the power supply reversed, can I just short across (or remove and solder a jumper) it's pins and up the Vref to 1.1V?  Pololu's spec shows 2.2A max (with additional cooling).  Id put some small heatsinks on the drivers, and a fan in the housing.

Pasted below for reference:

"The DRV8825 driver IC has a maximum current rating of 2.5 A per coil, but the current sense resistors further limit the maximum current to 2.2 A, and the actual current you can deliver depends on how well you can keep the IC cool. The carrier’s printed circuit board is designed to draw heat out of the IC, but to supply more than approximately 1.5 A per coil, a heat sink or other cooling method is required."

62
DIY AstroEQ / Re: Losmandy Titan stepper conversion
« on: April 14, 2015, 17:20:54 »
Tom, any thoughts on this?  I'm proceeding anyway, but am trying to guess.  Do you think that the Nema 23 - 270 Oz-in motor current limited will still be a lot more powerful than the Nema 17 - 76 Oz-in? I also have some tiny heat sinks that I can thermal epoxy on to the driver chips.

63
DIY AstroEQ / Re: Losmandy Titan stepper conversion
« on: April 09, 2015, 04:54:46 »
Hmmm... Ok

Do you have any thoughts on how much torque reduction?  I'm going from the 76 Oz In NEMA 17 to the 270 Oz In NEMA 23.  Any chance at 1.5 amps Ill get double the torque as the NEMA 17? 150 Oz In or more? If so my problem with the Titan mount may be  resolved with the motors I have, it's worth a try.  It's 100$ of motors after all.

64
DIY AstroEQ / Re: Losmandy Titan stepper conversion
« on: April 08, 2015, 16:55:00 »
Tom, Im assuming by limiting the current, I can still use these higher rated motors?

https://www.pololu.com/product/1478

They are 2.8A per phase @ 3.2V nema 23 @ 270 Oz-In

The motors from the above post were 1.68A per phase nema 17 @ 76 Oz-In

65
DIY AstroEQ / Re: Losmandy Titan stepper conversion
« on: April 08, 2015, 16:46:52 »
So I finally installed the AstroEQ a couple of weeks ago.  Unfortunately the motors weren't powerful enough.  It would work fine, then randomly it would screech in one or the other axis when a slew was requested.  I tried loosening the worm gear mesh a little, but it only helped in a small way. 

In the end I think I'm going to try some NEMA 23 motors I have.  Ill have to get new belts and a different mounting scheme. 

66
this is the motor/gear Im thinking of:

http://catalog.orientalmotor.com/item/packages-stepping-motor-driver-packages-0-36-0-72/eries-closed-loop-stepping-motor-drivers-dc-input/ar98ak-h100-3?plpver=11&categid=3001133&prodid=3001123&origin=keyword&selectedindexes=MTgxMjowfDE5ODI6OHwxODQ4OjB8MTgyMzoxfDE4NjE6M3wxODYyOjF8MTgxOTowfDE4Mjk6MHwxODQ1OjB8MTgyNDowfDE4NTg6MHwxODIxOjB8MTgzNzowfDE4NDM6MHwxOTY2OjB8MjAwMzowfA2&stditem#

here are the AstroEQ metrics:

Motor Step Angle: .38
Motor Gear Ratio: 1:1
Worm Gear Ratio: 100:1
Ustepping: 32

Gets a resolution of .405
Max speed sets to 1064

At 1300x2 it could be a relatively cheap Chronos call it a "Clonos" type setup.  Machining the rest would be much easier than worm gears etc..

Ill post more plans as I develop the idea more.

Tom,

Im not sure on the tricking the driver part as you posted previously.  If I set the stepping to 4, and the motor gear ratio to 25, the IVal drops to 143 based on the above.  If I leave the ustepping at 32 it gets an Ival of 399.  Either way, this is just a thought exercise at the moment.

If you get a chance, and by no means in any hurry.  Check the motor/driver specs above.  Most interesting to me is the "resolver" which sounds like on the front end it's a DIR/STEP controller, but internally it's using both step counting and the resolver for feedback.  Do you think this setup would work with AstroEQ/EQmod.  These motors look to possibly be the basis for a very beefy mount.

67
DIY AstroEQ / Re: Losmandy Titan stepper conversion
« on: January 19, 2015, 17:00:22 »
So I've ordered some new pulleys from a different supplier.  Hopefully they will be manufactured with greater precision.

Thanks for all the support on this Tom, I look forward to using it. 

68
DIY AstroEQ / Re: Losmandy Titan stepper conversion
« on: January 16, 2015, 20:46:23 »
News! 
Sorry to have wasted any of your time Tom if youve been scratching your head..

I just tried the EQMOD simulator and it does the same thing so I, next installed EQMOD on an entirely different computer that had MaximDL but never anything related to AstroEQ on it, set it up to use the simulator, and it did the same thing.

So it probably is just a display glitch with MaximDL and EQMOD..  Lots of people are using EQMOD with MaximDL for serious astrophotography..

69
DIY AstroEQ / Re: Losmandy Titan stepper conversion
« on: January 16, 2015, 18:58:08 »
ok.. doing some research here..

I still get the oscillation in MaximDL when the config program is using the following variables..

1.8
5.5:1
135:1
32 ustep

This gives a resolution of .273 steps per arcsec (the max I am able to get by fudging the numbers)



70
DIY AstroEQ / Re: Losmandy Titan stepper conversion
« on: January 15, 2015, 20:13:17 »
other than the above post, I am ready to try to install.  Being a remote installation, Im a little worried about one aspect.

Tom, I noted previously that I can see the crosshairs in maximdl for the telescope oscillate back and forth a tiny bit when zoomed in.

you had indicated when I first mentioned the problem that I should increase the microstepping.  I cannot.

Here is my metrics for the losmandy titan:

motor angle 1.8
worm gear ration 270:1
motor gear ratio 4:1 (40T pulley on worm and 10T on stepper output shaft) 
microstepping 16

My recollection is that if I try to choose 32, I get an error in the configuration program, possibly about Ival 

at stepping of 16 I get around .375 arcsec per step.  I though that would be sufficient as it matches what an EQ6 does.  I don't want to install this if tracking or gotos are going to be a problem.

Tom, your thoughts?

71
DIY AstroEQ / Re: Losmandy Titan stepper conversion
« on: January 15, 2015, 14:54:51 »
This is more of a mechanical question, but I received my XL timing belts yesterday.  All seems good, except now that I can actually spin the worm and the large pulley, I see that one of them has a bore hole that is slightly off center.  The whole assembly spins just fine, but it's creating a slight vibration in the entire worm block.

Anyone on here know if the tolerances will matter?  It's still a 10T xl pulley on the motor and a 40T pulley on the worm. 

72
Ok.. I see what you are saying..

73
I think I understand what you are saying about the math.  What I don't fully understand is why would that be necessary?

74
thanks for the reply, so yes, just a stepper driving a 160:1 harmonic gear head.  This would be inline like a chronos mount but instead of a Harmonic drive/AC servo/encoder, use a high count stepper.  No worm wheel or gear.  So in the configuration interface, either the worm or the gear ratio will be 160:1, as in one 160 rotations of the stepper = 1 rotation of the axis. This is why the number of steps has to be higher, even with microstepping. 


75
Hi Tom,

Still thinking of (possibly crazy) uses for astroEQ.  One idea I had was a high ratio harmonic gear head on a .9 degree stepper (or higher if there is a bipolar one available.  All the 1000 step steppers I've seen require a custom driver (which obviously could be interfaced with astroEQ with the right changes)

there are a wealth of harmonic drives on ebay.  Recently I saw this one which had a 260:1 reduction ratio.  Mechanical parts aside, it appears as if one could use a 400 step stepper at 32 microsteps and get over 5 degrees a second at .38 arcsec per step.

I have been putting in as follows:

stepper degrees:  .9
microsteps 32
gearbox ratio 260:1
worm ratio 1:1

Is this making sense?  I didn't use your configuration program because I have to have an astroeq or arduino connected (any way to make it have a dummy board attached for this spec-ing out purpose?) but rather I put the variables into onstep.xls which I found at stellarjourney.com (a very similar project but without eqmod compatiblity).  I've in the past put in these variables into your configuration program before though and gotten similar results.

So the questions are:


1. Am I crazy?
2. Is there a way to use the config program without an astroEQ attached just to use the calculations?
3. Can the worm ratio be 1:1 or does this break something?  I'm assuming in the end your software looks at a total reduction.
4. is a way for the layman to tell how fast it will go (*sidereal) without stalling the motor or missing steps? (the onstep.xls file does provide a maximum slew rate as part of the calculation, but it is based on interrupt rate and I have no idea what that means in this context.
5. Trying to get up to 1000 steps to improve resolution requires different drivers.  Oriental motor sells 1000 step steppers and these controllers:
http://www.orientalmotor.com/products/pdfs/2012-2013/A/usa_st_crk.pdf

interfacing with a controller like this would allow for higher spec motors.  Just wondering if you would ever consider (even for hire) to swap out the driver components/firmware that would allow this type of controller? Or will this project always stay with the easystep type drivers.

Refer back to question 1 if need be.


Thanks!  just thinking outside the box. In my mind the directly drive harmonic drive would be most interesting way to go on a custom designed mount.  Minimum of machining to be done..

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