Rotating the focuser for stepper motor

[sulaco]

Hi Folks,

I'm just about to undertake the popular Ascom focuser project and am planning to use the Nema17 PG27 geared stepper. This is all going to focus mu 130pds but having just received the motor it is quite heavy coming in at 410gm and should i connect it with a flexible direct coupling it may protrude over the end of the scope.

Is there any thought on rotating the actual focuser 180˚ so the weight is more central over the mount, I also have a Nema 14  (thin Round version)but with only 400 steps per rev but at a fraction of the weight and size.

Thanks for any thought on this.

Campbell

[ChrisLX200]

I don't know why the NEMA17 PG27 ended up the 'recommended' motor for this job, it's way over the top both in terms of weight and power for the job it has to do. As an alternative I'm using the NEMA14 19:1 motor which also has more power than needed but at least is somewhat lighter in weight and physically smaller. If you want to use a 17 size motor I suggest you mount it remote from the focuser and use a toothed belt to connect the drive to the focus wheel. By all means rotate the focuser if you can to the most convenient position (to keep the weight on-axis as much as possible).

ChrisH

[John78]

Put it on the other side of the focuser so it doesn't protrude?  Its easier to make a bracket to mount that way round also?

https://sourceforge.net/projects/arduinofocuscontrollerpro/files/Mounting%20Bracket%20Examples/Thomas-Jaeger-Focuser-1.jpg/download

[John78]

2 minutes ago, ChrisLX200 said:

I don't know why the NEMA17 PG27 ended up the 'recommended' motor for this job, it's way over the top both in terms of weight and power for the job it has to do. As an alternative I'm using the NEMA14 19:1 motor which also has more power than needed but at least is somewhat lighter in weight and physically smaller. If you want to use a 17 size motor I suggest you mount it remote from the focuser and use a toothed belt to connect the drive to the focus wheel. By all means rotate the focuser if you can to the most convenient position (to keep the weight on-axis as much as possible).

ChrisH

I've been looking at the project this morning and I agree a NEMA17 is overkill with a PG27 is ubermegaoverkill...

[sulaco]

Just got that pg27 yesterday and was surprised at the weight before I even opened the package. I came down from an 200mm scope to make it more light and compact. With your Neva 14 Chris what driver and arduino did you go for?

27 minutes ago, John78 said:

I've been looking at the project this morning and I agree a NEMA17 is overkill with a PG27 is ubermegaoverkill...

 

[Gina]

All my focusers use the 28BYJ-48 small stepper motor with gearbox and I find that plenty strong enough for the job.  It's small, light, cheap and readily available.  It has a 5mm shaft.  I can highly recommend these for this purpose (but not for clocks!).  They come in 5v and 12v versions.

[ChrisLX200]

Just now, sulaco said:

Just got that pg27 yesterday and was surprised at the weight before I even opened the package. I came down from an 200mm scope to make it more light and compact. With your Neva 14 Chris what driver and arduino did you go for?

 

It's the same firmware for either motor, but I've been playing with a variety of drivers. The simple version is to use a UNO+293D board, and that's what is driving my scope focuser right now. A better and more compact version is the NANO+8825 and I've made one of those up for testing.

ChrisH

[ChrisLX200]

2 minutes ago, Gina said:

All my focusers use the 28BYJ-48 small stepper motor with gearbox and I find that plenty strong enough for the job.  It's small, light, cheap and readily available.  It has a 5mm shaft.  I can highly recommend these for this purpose (but not for clocks!).  They come in 5v and 12v versions.

Yes those were the first motors I played with and likely they do have enough torque for most situations. For the benefit of Campbell I should point out I'm using a more powerful motor because I'm lifting a 5kg camera+filterwheel which is an exceptional load and I figured I would make certain I have enough power!

ChrisH

[John78]

6 minutes ago, Gina said:

All my focusers use the 28BYJ-48 small stepper motor with gearbox and I find that plenty strong enough for the job.  It's small, light, cheap and readily available.  It has a 5mm shaft.  I can highly recommend these for this purpose (but not for clocks!).  They come in 5v and 12v versions.

Looks like just the ticket, 64 steps per rev, 64:1 gear box, £3.89 delivered with a ULN2003 driver!

http://www.ebay.co.uk/itm/5V-28BYJ-48-4-Phase-Stepper-Motor-with-ULN2003-Driver-Board-Arduino-Pi-Pic-AVR-/281286257686?hash=item417df7ac16:g:q0EAAOSwjVVVwpEz

[sulaco]

Just checker that Nema 14 19:1 and at 100gm less it's a much better option for me, step angle's 0.094• so still fine. Back the others go then. Thanks

[ChrisLX200]

These are the 17 and 14 compared (17 in my hand)

and my latest version using a NANO and 8825 (recommended combination, but needs more soldering!). Note these are Rob Brown's MyFocuser2 circuit design and Arduino firmware ( https://sourceforge.net/projects/arduinoascomfocuserpro2diy/?source=navbar )

ChrisH

[sulaco]

There's a massive difference, I've just ordered the 14 and hope to get the rest of the parts this week. Thanks for the advice Chris

 

[sulaco]

I like the RP holder for the assembly, that's one of the smartest brackets I've seen.

 

[Dr_Ju_ju]

Nema 14 steppers work ok, these are fitted to my Newts, both belt driven

[fozzybear]

On ‎19‎/‎03‎/‎2016 at 18:25, Dr_Ju_ju said:

Nema 14 steppers work ok, these are fitted to my Newts, both belt driven

I'm looking to add auto focuser to my 150pds do you have a parts list of what to use ie arduino uno/nano and which nema14 motors and driver board

[ejp1684]

I found the round Nema 14 works fine with my 8" SCT. Powerful enough to move the mirror when the scope is vertical. The motor is controlled using Rob Brown's excellent DIY design.

Eric.

[Dr_Ju_ju]

9 hours ago, fozzybear said:

I'm looking to add auto focuser to my 150pds do you have a parts list of what to use ie arduino uno/nano and which nema14 motors and driver board

As Eric has said, there are a number of solutions based on arduino's, Tecky Dave's, Rob Browns etc... The parts list will depend on what you want as part of the set-up e.g. Bluetooth\Temperature probe etc.