Steppers for old mount question!
Posted 01 February 2011 - 11:47 PM
I have a big old Astro Optical EQ mount (Australian, could be same as US company) and between the previous owner and myself a number of embellishments have been carried out: Losmandy-style clutches, fine alt/az adjusters and a worm & wheel for the Dec axis (none in those oldies!)
I inherited older (non goto) EQ6 steppers and mainboard + handcontroller from the previous owner who had embarked on the Darren Hutchinson mods.....for the micro-stepping and ability via his software to compensate for varied gear ratios in different mounts.
This mount has a 169:1 RA worm and wheel and a 90:1 Dec w&wh.....with toothed drive belts this means I end up with the Dec panning out at 180:1 (which I believe is the ratio of both worms & wheels in an EQ6).....but the RA is 180.27:1
Hence the need to "tickle" the pulse rate of the RA stepper via Darren's software.....
My main problem has been that Darren seems extremely hard to get hold of (or get any info out of) these days - I don't hold that against him, and can understand why because of what he told me some time ago.....so I'm looking around for assistance/advice on ways of expediting me from my dilemma!
Just for the record, the previous owner made some very "untidy" work in building the DH kit.....it needs stripping and complete reconstruction/resoldering at the very least, and I could get another pcb made here (but don't want to mess around doing one myself!) so I've been looking at other options I might pursue!
One thought is cannabilising my current NEQ6 pro (approx 18 months old) for the steppers, mainboard etc and h/controller etc - and new ones are very cheap should I wish to buy another one for my other gear (especially with the $Aus at present)
This I thought would give me the high slew rate that is very handy imho: planetary imaging isn't terribly demanding on mounts as long as there's no vibration being transmitted through the gear train from the steppers.....and I'm assuming that I would have micro-stepping with these later NEQ6's, that the older ones didn't, as well - also assuming that they (Synta) still use 180:1 worms & wheels so that if the firmware can be programmed somehow, I could make up for that (small) difference between 180:1 and my mount's RA of 180.27:1
So, what do folks think - and being pretty ignorant about the whole process etc of altering firmware in general and stepping rates in particular to adjust for the (presumed) gear differences stated above, as one can with Darren's software and the older steppers.....is it practical, and how does one effect this....?
Posted 02 February 2011 - 04:55 AM
Get yourself the Orion dual-axis drive. This is stepper-based and for a 144:1 gear ratio. You can get one on ebay for $110.
I found out that on these primitive drives (I did an EQ-1M drive) the stepper driver is simply an 8051 microcontroller driven by a crystal.
In my case... the EQ-1 has a 100-tooth worm, but I put the drive on a Vixen Polaris (144-tooth). So the EQ-1M runs too slowly. I opened it up, replaced the 3.58MHz clock crystal with a (1.44 x 3.58 = 5.15MHz) 5.12MHz crystal (which was quite hard to find..) and voila.. it tracks well enough for visual purposes.
Now granted it's a bit too slow (not important for visual) but if you actually want to image, you can use a GPUSB. Even though the RA drive is ever-so-slightly slow (or fast, as the case may be) you can use PHD + GPUSB to apply guiding corrections via the directional buttons.
For visual... it should be good enough as-is.
Posted 02 February 2011 - 04:57 AM
Anyway the video capture / Registax can handle the planet drifting across the field, so long as the drift is very slow.
Posted 02 February 2011 - 06:11 AM
But I'll definitely look into the Orion dual-axis kit (just did a quick read) and yes, I think 144:1 is a bit slow and don't really wish to autoguide.....usually, because I traipse around the countryside a bit for my imaging my PA etc is such that the handcontroller is in fairly constant use (my planetary imaging is reasonably sophisticated imho! )
But I'll look at the various toothed belts I'll couple the stepper to the worm shaft with, and I may be able to close that gap considerably....!
Thanks for pointing out this option for me - I tend to be a bit myopic when it comes to net referencing.....anymore observations or ideas anyone has are still most wellcome...!!
Posted 02 February 2011 - 07:28 AM
Still haven't been able to find out what the EQ6 steppers are rated at, and I'll like to see what these Orion ones are rated at - 4 "D" cells would seem to indicate a pretty low current draw, and likely pretty low torque (the EQ6's aren't big current consumers, less than 2 amps @ 12volts for everything.....but that's a lot more "grunt" than you could expect from a 6 volt supply pulling no more than a few hundred milliamps at best.....but then again, the "Skyview Pro" mount it's made for is touted to handle 20lbs of OTA: and the steppers might handle higher voltages & currents.....
Posted 02 February 2011 - 07:53 AM
Posted 02 February 2011 - 08:55 AM
On EQMOD site they quote 180:1.. and not knowing how old that info might be I looked at the Skywatcher site and it states the same overall RA ratio of 705... so presuming that info is up to date I'd say they still use the 1:180
Hmmm.....thanks for that Russ - not sure what this "705" is meant to mean, although I think it logical their worm & wheel ratio of 180:1 is still valid.....would like to make certain though, because just buying a kit which are reasonably competively priced (about half that of a new NEQ6pro) would seem the obvious answer to my dilemma.
Looking at one (Oz) advertisement of an AA supplier reveals everything I need comes in the bundle.....and the extra money above alternatives seems pretty well spent.....