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[StuartLittle]

Hi Tom
Am very interested in your project, but have a few questions as I am working on a large custom mount:-
Do you do a self build kit?
Can I get the programme information for the programmed devices (where is it)?
I need to use different stepper drivers due to current required (I will be using Nema 23 steppers going upto 3 amps), do you have an alternative?
Can it support position senders/transducers?
Can it be made to support 64 microsteps?
Can it support the Synta handset?

I suspect the answer to a lot of these is to work it out for myself, but would appreciate any guidance you can give.
Cheers
Stuart

[TCWORLD]

Hi Stuart,

I don't offer kits, but all of the hardware designs, schematics, and parts list can be found here:
http://www.astroeq.co.uk/tutorials.php?link=/doku/doku.php?id=buildown

You can use higher power stepper motor drivers, you just need to find ones which have a "step", "direction" and "enable" interface which seems quite common, and also make sure it has the ability to set the microstepping mode via selection pins. You can also use higher voltage drivers if you want, but if you are going to do that, use a different 5V regulator for the rest of the controller (or even have an external 5V supply, only needs to be ~50mA).
In terms of microstepping, 32 is the maximum supported but I could change that in the config utility. One thing to be aware of is that there is a limit to the resolution you can achieve with AstroEQ - typically ~0.5arcsec/ustep. Using a higher microstepping mode like 64 may push you past that at which point the config utility will start indicating errors that the ratios are not possible. If you let me know what gear ratios you are planning on using and motor step angles I can have a look to see if 64 is possible.

The synta handset is untested. Theoretically if you add a port to connect it and logic level translation to ensure the signals are 5V TTL levels, it should be possible to connect the handset up as AstroEQ uses the same protocol. There are resistors in line with the TX/RX lines of USB-Serial IC in the schematic (The PIC IC could be replaced with an FTDI or other USB to serial circuit if you choose), you would connect the handset up on the ATMega side of those resistors which would mean that if a hand controller was plugged in it would take priority over USB. But again, this is not tested as I don't have one!

The protocol doesn't support position sensors and all of the positioning is done in software in the AstroEQ firmware. Unless you could ensure that your positioning system had the same resolution as one microstep it would be very difficult to rewrite the AstroEQ firmware to suit external encoders. So basically I have no plans to support external positioning.

If you have other questions or want to know if a specific motor driver will work etc. feel free to ask.


Regards,
Tom.




In terms of microsteps,

[StuartLittle]

Thank you very much for that Tom
My gear ratios are:-
RA 2880:1
DEC 1126:1
Both are running large (very large) worm and wheels (720 and 563 respectively) then through gears (4:1 and 2:1).  OTA is of the order of 300kgs.

I had looked at your tutorials wiki, but couldn't find any reference to the firmware for the programmed devices.

Thanks for your time.
Stuart

[pterodyne]

I was looking for the firmware myself..

It appears to be here:

 https://github.com/TCWORLD/AstroEQ

[StuartLittle]

Great!
Thanks Peter

[TCWORLD]

Hi Stuart,

Sorry for the delay getting back to you. With those gear ratios, you would be able to use 1/8th Microstepping at the largest. But even with that you would still get 0.28 arcsec resolution on the RA axis and 0.79 arcsec on the DEC axis.

So you would basically need a motor driver board for your motors which can support full stepping (for high speed) and 1/8th uStepping for low speed with some interface for AstroEQ to be able to select the mode.