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Author Topic: Increase the size of the Pulley's  (Read 2677 times)

rvaneynd

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Increase the size of the Pulley's
« on: November 01, 2017, 13:37:29 »

Thom,

I am using on my scope this kit: http://www.beltingonline.com/heq5-telescope-belt-mod-drive-kit-12097
Which uses the 60 Tooth pulley's

The setup I use is the AstroEQ box with a motorised EQ5 mount (using NEMA14 motors and the kit from BeltingOnline). 
If I where to change these to the 72 Tooth versions, would it increase the accuracy of my guiding?

Raoul.
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TCWORLD

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Re: Increase the size of the Pulley's
« Reply #1 on: November 01, 2017, 20:25:59 »

You can increase it, but it likely will make no difference to guiding. You would get a higher positional accuracy (arcseconds/microstep), but that doesn't really affect guiding.
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Tom Carpenter (AstroEQ)

rvaneynd

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Re: Increase the size of the Pulley's
« Reply #2 on: November 01, 2017, 21:41:40 »

Thom,

Thank you.

I was just thinking about smoothing the extremes on my PHD2 guiding and thinking that increasing the pulley size will enable AstroEQ to give the mount smaller adjustments and therefor making the PHD guiding more smooth.
Are there any parameters in AstroEQ that can help in smoothing the guiding? :-)

Raoul
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Zh

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Re: Increase the size of the Pulley's
« Reply #3 on: November 02, 2017, 11:21:11 »

Of course pulley size matters, but in my opinion much better (theoreticaly 2x) is using 0.9 degree steppers. Slewing time increases but smaller full steps leads to more precise small movements - i.e. guiding.
 Also very important is right current adjustement to stepper motors and even more important is the mount itself. It needs to be adjusted and greased for smooth movement on both axis, of course better if mount have some kind of ball or roller bearings whitch greatly helps for "unsticky" little movements mostly in DEC axis.
 Also for guiding mount balancing is very important, there are multiple methods, like precise balancing and precise polar alignment or precise polar alignment and slight disbalancing or even polar misalignment on purpose for steady guiding only to one direction.
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rvaneynd

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Re: Increase the size of the Pulley's
« Reply #4 on: November 05, 2017, 12:04:06 »

Okay, I have been playing around with the Config utility to test the different values.
My current config uses 1.8 Motor Step Angle. Gear Ratio of 4 and Worm Ratio of 144. = Resolution of 0.352 asec/step when using a 32 uStep.

Changing the motor to a 0.9 step angle version will double the resolution to 0.176 asec/step. Very nice.  :)
Increasing the pulley to 72 teeth will only improve the resolution by 0.059 to 0.293 asec/step.

And changing both will bring my resolution to 0.146 asec/step which is just an additional 0.03 asec/stp. So for the increase in 0.03, I will need to buy the 72 tooth pulley and new timing belts.

So the quickest and easiest solution is, as you said Zh, to change to 0.9 step angle motors.

But it does come at cost as the IVal will be small (between 194 & 146) with the result that my non-sidereal speed will be less accurate (This is the warning the config utility gives me). This can mean less accurate tracking on solar system objects.

So the ultimate question I need to ask my self is...
"How much do I care about accurate tracking of solar system objects vs a double increase in resolution for deep space objects?"

This is a difficult one, for which I do not have an answer at the moment.

Maybe the first question needs to be for you Thom, how big is the impact of this low IVal on non-sidereal accuracy?

Raoul.

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TCWORLD

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Re: Increase the size of the Pulley's
« Reply #5 on: November 05, 2017, 13:34:38 »

What it basically means is that there are fewer integer speed values.

The speed is calculated as:

Code: [Select]
Encoded Speed = round(IVal / Required Speed)
So for example if you wanted a speed of 3x the sidereal rate, the encoded speed value would be IVal/3. However as the encoded value is an integer, this value would be rounded to the nearest integer, so if you had an IVal of 100, the ideal encoded value for 3x speed would be 33.333, however in practice this would get rounded to 33 - an error of 1%. If you instead had an IVal of 200, the ideal would be 66.666, which when rounded to 67 gives an error of only 0.5%.

You can see from this that the larger the IVal, the lower the error. The error will also get larger the higher the speed - this is why the "Go-To" speed value changes when you update the configuration - it gets rounded to the nearest speed representable by an exact encoded value.

The reason for saying "non-sidereal", is that clear that regardless of the IVal, the encoded speed value will always be ideal (IVal/1 = IVal).

IVal > 300 should give a reasonable low-speed tracking performance. IVal < 50 are not possible because at that point the firmware can't produce a step rate which is fast enough. Hence the warnings in place.

In practice if you are guiding, this will be less on an issue as the guiding process will dither the speed. But there comes a point when the guide rate for the RA axis ends up achieving nothing - e.g. if you are trying to follow a satellite at say 10x speed, and your pulse guiding is 0.25x - you might find that speeds of 10x and 10.25x end up with the same encoded value and so the RA+ pulses do nothing.


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Tom Carpenter (AstroEQ)

rvaneynd

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Re: Increase the size of the Pulley's
« Reply #6 on: November 05, 2017, 19:02:17 »

Thom,

Thank you for the detailed and quick response.
At the moment I am not in to Satellites yet, but am aiming to image the ISS one day.
But not sure if for that one day I should hold off the upgrade.

Do you have any recommendations for NEMA14 0.9 Step Angle that work great with the AstroEQ?

Raoul
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Vic Thornley

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Re: Increase the size of the Pulley's
« Reply #8 on: January 26, 2018, 11:43:14 »

Hi Raoul and Tom. Have just got the stepper motors,  NEMA14 motors and the kit from BeltingOnline. Will be going to make the brackets, have the Skywatcher EQ5 mount with the dual axis kit. Can I ask if you have any photographs of it all set up on your mounts, so I can visualise what it should look like. Very much looking forward to this as I am currently stuck with with the slow slew rate of the dual axis kit. A photo would be a tremendous help. I have already made up the control box, only difference I did was to use red, yellow and green LEDs

Out of interest, I tried altering the voltages on the stepper motor drivers, I think i set them to around 2.5v and the dual axis kit motors got really hot - what voltage should I set them for the new steppers.

Cheers and thanks very much
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TCWORLD

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Re: Increase the size of the Pulley's
« Reply #9 on: January 26, 2018, 14:07:24 »

Do you mean altering the VRef voltage? That is changing the current limit not the voltage to the motors.

The Vref voltage should be equal or less than half the rated motor current (e.g. a 0.8A motor would be 0.4V Vref). Setting Vref to 2.5V would equate to basically no limiting at all (up to 5A), hence the motors get hot.
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Tom Carpenter (AstroEQ)

Vic Thornley

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Re: Increase the size of the Pulley's
« Reply #10 on: January 26, 2018, 15:29:19 »

Ah, cool - i understand it now. Is it possible of the photos of the custom pulley set up. I have an EQ5 mount (not the HEQ), so have gone for the same kit as Raoul, the teeth and belt specs are different to your sketchup plans. would i have to account for the differences.

Cheers, and thanks for the speedy reply.

Vic
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Victor_M

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Re: Increase the size of the Pulley's
« Reply #11 on: January 27, 2018, 13:10:01 »

Vi Vic,

you can read this post:
https://www.astroeq.co.uk/forum/index.php/topic,195.msg1200.html#msg1200

where you can find some pictures from some people (included myself - Skywatcher EQ5 mount) about the gears and motors attached to the mount
cheers
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Vic Thornley

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Re: Increase the size of the Pulley's
« Reply #12 on: January 28, 2018, 13:12:05 »

Hi Vic

Great stuff. However, i have the HEQ5 mod kit from belting online, I had to bore the 9mm holes up to 12 mm. I am now in the process of sizing up the brackets. This thread will be a  great help to me. Thanks very much.
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