Stepper Focuser for 200P

[SnakeyJ]

Having a weeks holiday and bad weather, I've finally decided to unpack this shelved project!

A little work this afternoon shaping the mounting bracket, made to fit over the Lacerta 10:1 focuser upgrade on my stock synta focuser.

Looks good from this angle:

Whoops! Spot the deliberate mistake:

Pesky flanges on those gear wheels!    Measure twice, cut once and all that - though in this case I will simply move the mounting screws 5mm in and shorten the bracket.

The stepper mxl wheel is 20 tooth and I want this to drive the 10:1 reduction gear with an 168mm belt (measured length).    MotionCo, only stocked 80 and 90 teeth belts - but I managed to find 167mm and 173mm belts at BeltingOnline, which comfortably brackets and should allow me to fit with a small adjustment.

Now I need to find the SGL focuser thread and see if I can get a response on the sketch and Ascom driver - Arduino at the ready

[SnakeyJ]

I meant to add that the motor is a 28BYJ-48:

Rated voltage ： 5VDC 

Number of Phase 4 

Speed Variation Ratio 1/64 

Stride Angle 5.625° /64 

Frequency 100Hz 

DC resistance 50Ω±7%(25℃) 

Idle In-traction Frequency > 600Hz 

Idle Out-traction Frequency > 1000Hz 

In-traction Torque >34.3mN.m(120Hz) 

Self-positioning Torque >34.3mN.m 

Friction torque 600-1200 gf.cm 

Pull in torque 300 gf.cm 

Insulated resistance >10MΩ(500V) 

Insulated electricity power 600VAC/1mA/1s 

Insulation grade A 

Rise in Temperature <40K(120Hz) 

Noise <35dB(120Hz,No load,10cm) 

Model 28BYJ-48 – 5V 

 

Drver board is the ULN2003.

[Gina]

Same as I'm using on my scopes.

[tekkydave]

Same as I'm using on my scopes.

Snap!

[SnakeyJ]

It was one of Gina's threads that put me on to the motors

[Dave_D]

i'm using a 12v... i like to be the odd one out 

[Gina]

I'm using 12v ones for my CCTV cameras.  Just depends on what voltage is most readily available

[SnakeyJ]

Hmm looks like Chris's code/wiring is specific to the Easydriver, rather than ULN2003 - might have to source the preferred stepper driver!    First up I'll have a scan through the sketch and see if there's any room for manoeuvre...

[JamesF]

Looks promising, Jake.  I have to say that nothing has increased the enjoyment of the imaging process more for me than having a motorised focuser.  Making it work is time well spent.

James

[JamesF]

As a bit of a random aside, have you seen the Baader Steeltrack focusers?  I'm not suggesting anyone should rush out and buy one, but if you look at the slow-mo knob on them they have a section that is specifically machined to fit an HTD (I think) drive belt.  That's smart design

James

[SnakeyJ]

Looks promising, Jake.  I have to say that nothing has increased the enjoyment of the imaging process more for me than having a motorised focuser.  Making it work is time well spent.

James

Thanks James - I did have a prototype standalone unit, with 4 push buttons and a 16 char LCD, though never got as far as mounting this on the scope.   It sort of worked, but was rather flakey mainly as the switches were so cheap and nasty - never did get the lid closed on the project box

It will be much nicer to have direct and ascom control from the laptop, especially with direct control via APT and Firecapture.   One day I might even be able to retire to that warm room or control remotely from the conservatory for those cold clear winter nights - though after 2 years, I'm beginning to think they are a bit of a myth in these parts at least

[SnakeyJ]

As a bit of a random aside, have you seen the Baader Steeltrack focusers?  I'm not suggesting anyone should rush out and buy one, but if you look at the slow-mo knob on them they have a section that is specifically machined to fit an HTD (I think) drive belt.  That's smart design

James

Certainly have and the Baader steeldrive unit looks very nice indeed - but £ 500+ for the both looks steep.    I'm keeping an eye open for a 10" OO VX, which comes with the same focuser (unbranded steeldrive).   However, unless flush will probably keep the SGL focuser and stepper to drive.

[JamesF]

I quite understand.  There are a whole load of astronomy-related things that I think "That's nice, but if I want one it will only ever be second-hand"

James

[Gina]

As a bit of a random aside, have you seen the Baader Steeltrack focusers?  I'm not suggesting anyone should rush out and buy one, but if you look at the slow-mo knob on them they have a section that is specifically machined to fit an HTD (I think) drive belt.  That's smart design

James

Yes, I'm using a Baader Steeltrack focuser on one of my Evostar 80EDs and am using an HTD drive belt from the my Ardiuno controlled stepper motor.

[SnakeyJ]

I took the easy route and ordered a couple of Easydrivers today.

I did take a quick look in Maplins today - hopeless!

[SnakeyJ]

C'mon postie........

[SnakeyJ]

Top marks to Belting Online (and the Royal Mail), both belts received this morning.   The 167mm was too small, but the 173 looks comfortable with minor adjustment to tension or even a sprung tensioner - this might be handy for clutching should I need to manually adjust.

Hopefully the Easydriver boards will arrive tomorrow

[SnakeyJ]

Rats!

The Easydriver board arrived today and I made a special journey in to work to pick up my solder station.    Just got set up ready to roll and the darn thing (Weller WD1) has gone and died on me - no LCD display and no heat at all at the wand.

A quick check with the multi meter shows that the obvious fuses and internal transformer are working, but otherwise like the proverbial Dodo

Too good to throw away, but can I get it sensibly repaired in UK?    £ 165 for a replacement PSU on ebay, or marginally higher at Farnell's.....

[szymon]

Since you're handy with a soldering iron, ask for some help on eevblog and get cracking ;-).  Alternatively take it to a local radio ham (be careful to find one that actually knows how to solder and undertands electronics, there are quite a few new ones in the hobby now who just passed a 'foundation' license where you basically just prove you can talk on a radio, but old school amateurs are experienced and and will help).

-simon

[SnakeyJ]

Since you're handy with a soldering iron, ask for some help on eevblog and get cracking ;-).  Alternatively take it to a local radio ham (be careful to find one that actually knows how to solder and undertands electronics, there are quite a few new ones in the hobby now who just passed a 'foundation' license where you basically just prove you can talk on a radio, but old school amateurs are experienced and and will help).

-simon

Thanks Simon - quite a useful thread over on the eevblog site, http://www.eevblog.com/forum/repair/weller-wd1-discussion-and-repair/msg209609/#msg209609 

These guys know a world more than I ever will about the electronics!   I'm going to follow your second suggestion about the local radio ham - there's a chap just down the lane who's part of RAYNET and may be able to help or point me in the right direction.

[tekkydave]

Since you're handy with a soldering iron, ask for some help on eevblog and get cracking ;-).  Alternatively take it to a local radio ham (be careful to find one that actually knows how to solder and undertands electronics, there are quite a few new ones in the hobby now who just passed a 'foundation' license where you basically just prove you can talk on a radio, but old school amateurs are experienced and and will help).

-simon

Thanks for the heads-up on eevblog. I didn't know it existed. Very useful to know.

[szymon]

Yes it's a great site with a lot of very helpful people :-)

Sent from my iPhone using Tapatalk

[tekkydave]

Yes it's a great site with a lot of very helpful people :-)

Sent from my iPhone using Tapatalk

Ive registered as tekkydave.

[SnakeyJ]

Bit hung up without the soldering iron - but it did force me to rethink the connectors between the stepper and control box.   Originally I was going to use conventional 9 pin d subs, but I found some old Cannon ITT jacks which make quite a nice solderless alternative and keep the weight down.    The jack was epoxied down to the aluminium plate after crimping.

Looks neat and I can easily knock up a patch lead to suit.

[leelee970]

Very interesting, you've made me think about mine now.

More money going to be spent, oh well, you can't take it with you when you die I guess.

Lee