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[pterodyne]

Hmmm... Ok

Do you have any thoughts on how much torque reduction?  I'm going from the 76 Oz In NEMA 17 to the 270 Oz In NEMA 23.  Any chance at 1.5 amps Ill get double the torque as the NEMA 17? 150 Oz In or more? If so my problem with the Titan mount may be  resolved with the motors I have, it's worth a try.  It's 100$ of motors after all.

[pterodyne]

Tom, any thoughts on this?  I'm proceeding anyway, but am trying to guess.  Do you think that the Nema 23 - 270 Oz-in motor current limited will still be a lot more powerful than the Nema 17 - 76 Oz-in? I also have some tiny heat sinks that I can thermal epoxy on to the driver chips.

[TCWORLD]

I can't say for sure. The only thing is if the current is too limited, the voltage across the motor coils will never reach its rated level (because of inductance), so you may find they perform worse! Or they may perform better. But either way it will be less than 270 oz-in.

[pterodyne]

Tom,

You mention earlier in this thread that the max Vref*2 for setting the current is .72V which puts us at 1.44A.  The reason you cite is the reverse polarity diode on the AstroEq board.  Assuming I never plug in the power supply reversed, can I just short across (or remove and solder a jumper) it's pins and up the Vref to 1.1V?  Pololu's spec shows 2.2A max (with additional cooling).  Id put some small heatsinks on the drivers, and a fan in the housing.

Pasted below for reference:

"The DRV8825 driver IC has a maximum current rating of 2.5 A per coil, but the current sense resistors further limit the maximum current to 2.2 A, and the actual current you can deliver depends on how well you can keep the IC cool. The carrier’s printed circuit board is designed to draw heat out of the IC, but to supply more than approximately 1.5 A per coil, a heat sink or other cooling method is required."

[TCWORLD]

You can remove the diode, yes, as long as you ensure you never connect the power up in reverse as it would completely destroy the entire controller.

However you can't go to 2.2A without significant cooling - in fact active fan cooling. I've tried with these drivers before to drive a high current NEMA17 motor (2.1A/phase), and if I went any more than around 1.8A/phase through the driver chips with a small heatsink, they would simply overheat and engage their thermal protection (switch off for half an hour or so before finally starting to work again).
I designed a circuit board for that motor which had a very carefully laid out thermal management, the thermal pad on the back of the IC was attached to the PCB and then routed through very thick vias to the back of the board where there was about 2 square inches of copper fill on the PCB attached to a 2"x2"x8" aluminium block with thermal paste. Even in that situation, I can't get the current to more than 2A/phase reliably (without tripping the thermal protection).

You can try bypassing the diode and using 1.8A/phase with a heatsink which would give you a bit more power, but nowhere near the rated 2.8A.

[pterodyne]

It's been a long time, but after several years of having a sitech servo 2 on the titan,(which started having problems), I decided to finish my titan conversion to astroeq.  Originally I was using onstep, but a little late night in observatory soldering fried my board.  Anyhow, I now have a Losmandy Titan with NEMA 23 1.5A motors running astroEQ.

See attached pictures. The overall pic still has the Sitech on it.  Nice to see AstroEQ can be used on a mount this size.  I have to limit my speeds to around 300x, but since it's all automated , that doesn't matter much. The stepper mounting brackets were designed using emachineshop.com CAD software and machined by them.  Perfect!

Stats

Losmandy Titan
270:1 Worm wheel
3:1 GT2 pulley reduction
Stepper Online NEMA 23 1.5A Bipolar steppers
AstroEQ with DRV8825 (fast decay hack)