Driver for microstepping

[schneiderj]

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 :

• L6470 from ST microelectronic
• A3959 from Allegro
• drv8824 from TI

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

[vger]

The L6470 is programable and has motion control built in.. it would probably be the most difficult to use.

The A3959 is a PWM driver for servo motors....

The DRV8824 will probably be the easiest for you to use and interface to the PIC.

Some of the DIY telescope drives I have seen use very large worm wheel drives. A 360 tooth wheel with a 200 step/rev stepper running at 1/32 step would give you 0.5625 arc second steps, or 0.000015625 Degree steps.

Steve

[schneiderj]

Thanks Steve for you explanation. So I will focus on the TI technology.

For the reduction, I will use a worm wheel, but with a lower reduction than those we can found on a lot of mount. You will found in the pdf file What I am working on. And here a picture of the mount at its actual state :

http://static.electro-tech-online.co...resize_110.jpg

By this way I am expecting to lower the periodic error which is the nightmare of telescope mount. And the final touch will be the use of an encoder put on the wheel and to control the motor with it.

Jean-Marie

[vger]

Jean-Marie,

Are you planning to belt drive the wheel? And perhaps belt drive back to the encoder?

Steve

[schneiderj]

Originally Posted by vger Jean-Marie, Are you planning to belt drive the wheel? And perhaps belt drive back to the encoder? Steve

This is one option, but in this case I will drive the encoder directly from the wheel.

But my first trial will be done with a bell sticks on the big wheel (bell will be reversed : inside will be outside and vis versa, not such that explanation is understandable). The small wheel (the second one on the same axe as the one of the worm gear) will be directly in contact with this in contact with the past bell. A second wheel will be in contact with the bell with the same principle and will drive encoder.

I am expecting you can understand what I means...

Jean-Marie

[schneiderj]

Hello,

some of you have been tested LiniStepper ?

Jean-Marie

[tommylight]

Yes i did try linisteppers and they work like a charm, i also have geckos and some other drivers, but for the money you won't find anything better than lini's .

[James Newton]

Thanks for the kind mention tommylight. Roman and I were just talking the other day about telescope mounts. Because the Linistepper supports /very/ smooth analog microstepping, we have long thought it would be ideal for driving equatorial mounts.

I'm interested in investing in development of a driver for ASCOM or other PC software to talk to standard stepper drivers like the Linistepper (or gecko for larger motors). I'm amazed at what people are paying for these systems. The mechanical parts and electronics just aren't that complex, the only thing stopping the wide use of stepper motors and drivers is the lack of an interface to ASCOM.

Open source drivers ARE available for EQ mounts, but not for standard parallel stepper interfaces; for example, EQMOD supports only a specific set of drivers and does so through a serial interface.
EQMOD

These guys are trying to write one, and have published some code:
Ascom-Telescope

I'm interested to hear what people think about this...