Driver for microstepping

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schneiderj

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Hello,

I will developpe a motorisation for my telescope mount (I know that a lot of system are already existing as commercial or free product) to personnalise it a little bit more.

There is two key points : the mecanical part and the command of the motor.

I would command the motor with a PIC 32 (to be able to compute cosine and sinus). As driver I found three products which same interresting :
Which comments can you tell me about these drivers (facility to use, efficiency, ...) ?

And a second questions : did you know a good book on stepper motor (and not too old) ?

Thanks you for your help,
Jean-Marie
 
Different circuits can drive different loads. You haven't provided any info about the stepper you're gonna use so you can't expect anybody to pick the "right" ic for you.
Ie - how big is your telescope and how fast will the motor run, and do the stepper need do be strong?
 
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Hello,

you are write !

So I upload the reduction worm I am working on. Reduction will be 34 for 1. And the second reduction will be 8 for 1. And finally a picture of the mount as it is actually :
**broken link removed**.

Motor will be a Nanotech : ST5709S1208 with the following data's :

**broken link removed**

I will it in parallel mode.
During normal motion (360 ° per days) I need very slow motion with the best accuracy possible : let says 0.5".

With this reduction and the 400 steps per revolution of the stepper motor that gives 108800 step for 1 rotation of the hourly axe (or 1296000 ").

By the way I need at least 24 microsteps per step or 1 revolution of the stepper motor for a little bit more than 5 minutes.

For fast motion I am expecting to have one to two revolutions of the motor per second.

I thinks that all informations I have.

Jean-Marie
 

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I am just getting into steppers myself. Do you really want to build the stepper driver board? Buying one would be less problematic.

The L6470 from ST microelectronic look interesting but I am not quite sure how to work out if it can provide the current you need.
 
For microstepping a bipolar stepper motor you can't go past this circuit **broken link removed**
and a pic 32 is way overkill for a simple project of this nature. The above circuit uses a 16f628a chip and any other low pin count 16f chip would do the job of interfacing the circuit. I have designed a double sided board for that circuit in sprint layout and I'll be happy to post it here if you want.

Regards Bryan
 

Thanks for your answers and comments.

But I will need this PIC32 for the next steps of this project : for the moment the mount is an equatorial one, but I will transform it to an azimuthal when equatorial axe will be correctly managed. At this time I will have to calculate sinus and cosine with a precision of 10^(-15) and this many times per second.

And I would like to have a system completely open to be able to drive the two motors together with high precision optical encoder.

Jean-Marie

EDIT : the L6470 look very interesting, but I am unable to find it. I found only the eval board. Did you know why ?
 
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I would build the stepper controller as Brian suggested and then have your PIC32 talk to it. The code for that controller is in ASM. That will allow you to code the rest of the application in the language of your choice.
 
Have a look at the Linistepper stepper motor driver. It contains a PIC and microstepping circuitry that can be "tuned" to be very smooth at a particular speed. Also as it has the on-board PIC (with open-source .asm code) you can set the one PCB up to turn your telescope to match earth's rotation.

I recently built a 6-hour rotation stepper motor clock, the same code can be used for telescope rotation;
**broken link removed**

Some of the guys use Linisteppers for telescopes because they can use the on-board PIC and xtal for accurate rotation, and for a fixed speed there are 2 caps that can be used to completely smooth the stepper microsteps making it the smoothest stepper motor driver available.
 
Thanks for your answers.

I have a question : what will be the advantage of these LiniStepper or PicStep over the drv8824 or L6470 ?

And cost saving same not obvious : the TI chips cost less than 10 $ (I did not find a price for the ST one).

What did you thinks ?

Jean-Marie
 
I would go with the LinStepper for the reasons RB stated. People are already using it for your application and it is smooth.
 
OK, I have ordered one kit to test this linistepper.

Did some of you test the accuracy of the motor with an encoder for example ?

Jean-Marie
 
Hi Jean-Marie,
I had a good read of the linistepper and it does look great but it is only for unipolar motors and the stepper you said you were going to use is Bipolar. Hopefully you haven't already bought that bipolar stepper as it won't work with the linistepper. The reason I suggested the pic step was based on that post where the bipolar stepper spec's were shown.

Regards Bryan
 
His motor has 8 wires, and can be wired in unipolar OR in a couple of bipolar version; series parallel etc depending how he connects the wires. It should be ok.
 
I put together a really simple design for a telescope system. An AC timing motor where the frequency is varied. A square wave was used to drive the motor. He only need 60 Hz and wanted it battery powered, so you just drive a center-tapped transformer in reverse putting the 12 V on the CT and pulse the ends.

This is much smoother than a stepper could ever do.

I do understand steppers, but I lost all of my material. First, there is the understanding of Bipolar and Unipolar, voltages used and nameplate voltages.

Then add overcurrent protection for the drivers.

Now try to add microstepping to the mix. Microstepping is basically holding the current somewhere between two values.
 
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