openDrive <-> Ethersex <-> SkySafari

[rmike]

Hi,

here's a small video of our openDrive project:
http://www.youtube.com/watch?v=PWyo-2PWCHA (https://service.gmx.net/de/cgi/derefer?TYPE=3&DEST=http%3A%2F%2Fwww.youtube.com%2 Fwatch%3Fv%3DPWyo-2PWCHA)

That's just a demo with hard coded motor and mount parameters etc.

openDrive is a open source / open hardware project for a scalable, freely available telescope drive system for equatorial and alt-azimuth mounts.

The modular design is based on stackable PCBs. See here for details: https://github.com/selste/openDrive/wiki/Hardware (https://service.gmx.net/de/cgi/derefer?TYPE=3&DEST=https%3A%2F%2Fgithub.com%2Fsel ste%2FopenDrive%2Fwiki%2FHardware)

Some facts about our current stepper motor driver board:

- capable of delivering 2.5Aeff/coil (=5Amax/motor)
- 64 microstep resolution
- up to 30V operation (it's spinning up to 20rps with a Escap P530 in the above video with 24V)
- based on TMC428/429 and TMC249 from Trinamic


CPU board:

There will be a cpu board based on ATmega1284p and the great ethersex project (https://github.com/ethersex/ethersex (https://service.gmx.net/de/cgi/derefer?TYPE=3&DEST=https%3A%2F%2Fgithub.com%2Feth ersex%2Fethersex) and www.ethersex.de (https://service.gmx.net/de/cgi/derefer?TYPE=3&DEST=http%3A%2F%2Fwww.ethersex.de)) . And an optional linux add on, probably based on the raspi (raspberrypi.org) for more complex things like pointing models, large catalogs, webcam based auto guiding etc.


Maybe some of you folks like to join the development?


Regards,
Michael

[bojan]

Hi Michael,
This is very impressive :-)
I had a look at trinamic data sheet, and tried to opn sch file (with altium) but obviously, it is not in altium format (it is Eagle, right? I will have to download the demo to have a look.. do you have pdf version?).
The reason is, I already use Mel Bartels software, and I was hoping that your motor control board can be controlled with step-dir pulses. 64microsteps sounds like exactly what I need for my timing-belt modified EQ6.
All in all, very interesting project :-)

[rmike]

Hi bojan (http://www.iceinspace.com.au/forum/member.php?u=1131),

these are eagle files (www.cadsoftusa.com (http://www.cadsoftusa.com)).
The boards are designed within the limits of eagle light edition (max. 80mm x 100mm, dual layer).

You could get rid of the TMC428 and drive the TMC249 directly with step-dir pulses but you would loose 64 micro stepping and most of the other advantages of the board.
The TMC428 calculates the acceleration and decelerations ramps on its own.
This is great because you don't need to deal with timing critical things in the rest of your firmware...

Michael

[bojan]

How do you communicate with the motor driver board? SPI ?

[rmike]

Hi,
yes.
There is an additional chip select demultiplexer.
So you have to set up CS_A,CS_B and CS_C to the right board address first.
Max motor current is set through PWM.

The board is my first shot with these circuits, but runs quite well.
There are some small changes described here: http://opendrive.gizmor.org/forum/viewtopic.php?f=6&t=17
You could use http://translate.google.com/ for a translation.

Michael

[alistairsam]

Hi Mike,

very interesting. I've been looking at the trinamic chips for a while and the 429 features are very impressive, especially the automatic ramp calculation, stall detection and coolstep.

is there documentation for the set of commands you send to the trinamic chips so other mcu's could be used? are there details of these commands? how is the output from skysafari interpreted by the mcu?

from what I understood, you can give absolute or relative positions to the 429 and it calculates velocity, acceleration and deceleration.
so can these commands be sent via serial or I2C from a different mcu?

how does the feedback work? how does the 429 know the position of the mount? reason is because I don't have an eq6 but have built my own drive and interface is with picaxe mcu's that work well with serial input and output as well as I2C.
I've programmed them to emulate the LX200 protocol so it understands LX200 commands and will respond in the correct format.

do you have a flowchart of how the different components integrate including feedback?
The trinamic chips have dropped in price now and are available through element14, but the evaluation boards are quite expensive. is your board similar to the trinamic evaluation boards?
I tried opening the .sch file with designspark but couldn't.

Thanks

[rmike]

Hi,

i there is also a thread on CN about this and i don't want to repeat myself:
http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Number=4942046

Regarding TMC428/429:
Please take a look at the Trinamic web page. There is plenty of info about the chip with code examples etc. As already written above it talks SPI and no I2C.

Michael

[rmike]

Hi alistairsam,

parts for our motor driver board cost around 65 EUR in single quantities in Germany.
I have no clue about component prices in Australia.

Last week an alternative board from Trinamic appeared on the market:
http://www.trinamic.com/tmc/render.php?sess_pid=493
It is even more powerful than our design with a cortex mcu already build in.

My code talks LX200 with the ipad.
I'll publish my code on github soon after cleaning it up.

Michael

[alistairsam]

The steprocker is pretty cool. not sure when we'll be able to get it here though.
When possible, it would be good to see the LX200 interface logic and how the feedback works.
I've been through the tmc math on your page, thanks.

I presume your project was to develop an interface for any generic scope, not just the eq6 as the eq6 can be interfaced with sky-fi and ipad/ipod quite easily.

do you specify the gear ratios in your mcu firmware so it can calculate relative target position values for the trinamic 429?
eg. to move 10 degrees, the mcu would know the gear ratio and ask the 429 to move from position x to y and the 429 does the rest?

have you thought about automated focusers as well as the stallguard feature would be ideal for focuser applications to detect home position.
I think one user in this forum has been trialling this.

[hikerbob]

Alistairsam, I've tried to experiment with the TMC223.
Not much success so far, my surface mount soldering needs some work as does my understanding of I2C. Had a little bit of success then it stopped.

One of those things I plan to revisit when I'm less tired in the evening (very busy at work at the moment).

Bob