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Author Topic: REVAMP MY HD MOUNT  (Read 3667 times)

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Offline jhughe22

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Re: REVAMP MY HD MOUNT
« Reply #15 on: 09:05:22, 15 April, 2016 »
I wouldn't try running stepper motors at 600RPM. Not to say it couldn't be done, but that sounds quite fast for a stepper motor. Depends on huge number of factors.

Stepper motor torque reduces as speed increases. It depends on the motor but at that sort of speed I would expect to only have 10-20% of the torque available.
Yes I remember reading that somewhere, so if I wanted to replace just the motors they would have to be 12v or 24v DC motors and use a PWM to control the speed?? 
However I just managed to bag two PHILIPS MB01 motors (torque 380 mNm, 1.8deg, current class 1a) with Mclennan 50:1 gearboxes, hopefully I will be able to use one of these to achieve the 0.333RPM required.   :D
8" f/5 Sky-watcher 200P f=1000,  6" f/9 Ritchey-Chrétien Revelation Astro f=1370, 3.5" f/10 Meade 90 with 2" focuser mod f=900, 3.5" f/13 Maksutov-Cassergrain f=1200...  Heavy Duty EQ est-60lb payload.  iOptron Minitower v2, Skywatcher SupaTrak, and a damaged EQ-3 Mount. Latest;- EQ-5 with dual drive.
Camera's;- Nikon D5000, Sony Nex5, Samsung NX2000, Altair GPCAM AR0130C, Celestron NexImage SSI

Offline jhughe22

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Re: REVAMP MY HD MOUNT
« Reply #16 on: 09:13:30, 22 April, 2016 »
Update on my progress   :laugh:  I have experimented on the Philips MB01 steppers, and have found some useful results. I connected one motor to the RA channel of my Sky-Watcher Enhanced hand controller, and found it has a 2.875RPM  with a very high torque, also the 16x and 2x speeds run very smoothly.  I also purchased a StepperBee+ PC adapter and  after much experimenting was able to (via the laptop) continuous step at an interval time of ms750 in a closed loop, which gave me the desired 1/3RPM .  However  after a while the motor became hot :ugly: 
I am therefore inclined to use the SW Hand Controller and rig up a drive belt 3:1 gear.  However i'm having difficulty in sourcing belts gears etc  :no:  I'll keep on chipping away  :laugh:
8" f/5 Sky-watcher 200P f=1000,  6" f/9 Ritchey-Chrétien Revelation Astro f=1370, 3.5" f/10 Meade 90 with 2" focuser mod f=900, 3.5" f/13 Maksutov-Cassergrain f=1200...  Heavy Duty EQ est-60lb payload.  iOptron Minitower v2, Skywatcher SupaTrak, and a damaged EQ-3 Mount. Latest;- EQ-5 with dual drive.
Camera's;- Nikon D5000, Sony Nex5, Samsung NX2000, Altair GPCAM AR0130C, Celestron NexImage SSI

Offline chris.bailey

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Re: REVAMP MY HD MOUNT
« Reply #17 on: 10:11:54, 22 April, 2016 »
How hot is hot? Steppers can run quite warm i.e just uncomfortable to the touch. On some of the drivers there are options for stepper power on or off. When on the coils are constantly powered to provide holding torque, handy for focusers. They run a few degrees cooler with stepper power off though yours are constantly driven so that may not help.
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Offline ChrisLX200

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Re: REVAMP MY HD MOUNT
« Reply #18 on: 10:21:42, 22 April, 2016 »
It's not unusual for a stepper to get hot, most are designed to run that way and they can actually feel too hot to hold yet still be operating within spec. However, you can control heat generation to some extent by moderating driver current - though I don't know if it's possible using a 'StepperBee'. If you used a DRV8825 you can measure the current used per phase and set it (using a tiny trimmer pot on the driver board) to a lower value. If the coils are left powered up on a non-moving motor (say, the DEC motor which is only used intermittantly) then that would generate heat needlessly - well it's 'needless' if you don't need the holding torque anyway (which you actually do for a focus motor because you want it to hold position when stopped). Using an Arduino or Raspberry Pi to interface to a driver board would give you finer control I suspect, and would be a stand-alone solution that doesn't need a PC.

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Offline jhughe22

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Re: REVAMP MY HD MOUNT
« Reply #19 on: 12:21:31, 22 April, 2016 »
Thanks Chris and Chris, the DRV8825 driver looks interesting.  When I ran the stepper using  StepperBee it got hot but not unbearable to touch and I was able to run at 1/3RPM.  But like I said the SW Hand controller gives me the desired control if not the correct RPM, solution is to gear down 2.87 RPM to 0.333RPM required. I've been unable to find any cogs with the same pitch as the 12mmDia 23tooth cog attached to the spindle of the stepper. So it's either make my own pulley timing belt setup or try buy some already made ones !  :D
John..
8" f/5 Sky-watcher 200P f=1000,  6" f/9 Ritchey-Chrétien Revelation Astro f=1370, 3.5" f/10 Meade 90 with 2" focuser mod f=900, 3.5" f/13 Maksutov-Cassergrain f=1200...  Heavy Duty EQ est-60lb payload.  iOptron Minitower v2, Skywatcher SupaTrak, and a damaged EQ-3 Mount. Latest;- EQ-5 with dual drive.
Camera's;- Nikon D5000, Sony Nex5, Samsung NX2000, Altair GPCAM AR0130C, Celestron NexImage SSI

Offline tomhow

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Re: REVAMP MY HD MOUNT
« Reply #20 on: 19:12:49, 26 April, 2016 »
I've used a stepperbee. They are great devices for learning the basics, but they are not very sophisticated and don't offer any current limiting.

Moving up to the DRV8825 is a great option. Although you will need something to generate the step pulses -  e.g. a microcontroller/arduino. You can't just plug it into a usb port.

The idea with stepper motors is to use quite high voltage, e.g. 12v or 24v and the controller uses PWM to limit the current to the coils.

These days, unless it is a small motor (when I use a DRV8825) I tend to use one of the driver boxes designed for DIY CNC. e.g. https://www.cnc4you.co.uk/Stepper-Motor-Driver-4.5A,-50V-CNC-Microstepping-CW5045?search=stepper%20motor%20driver these sort of devices do excellent microstepping and current control. Nice self contained box with terminals.. No phaffing about. Again, you need a microcontroller to generate the step pulses.



e.g. the stepper motor I use to drive my dome uses

https://www.cnc4you.co.uk/Stepper-Motor-Driver-6.0A-20~60VAC-or-24~80V-CNC-Microstepping-CW6060AC?search=stepper%20motor%20driver
https://www.cnc4you.co.uk/Stepper-Motor/Nema34/Stepper-Motor-8.7Nm-86HS115-4208-Nema34
plus an arduino to generate the step/dir pulses.
....along with a 36v power supply.

...note that the "rated" voltage on a stepper motor means nothing if the controller does current limiting. Higher voltages are used to step faster (the coil current decays faster, or something).

Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

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Offline jhughe22

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Re: REVAMP MY HD MOUNT
« Reply #21 on: 08:34:36, 27 April, 2016 »
Tom i've found a 555 with 4013 flipflop circuit which I believe which will generate a variable pulse frequency which I will pass onto a L298N Dual H Bridge Stepper Driver.  With a few changes I should be able to add a 2x and 5x and use the 100K pot to trim the sidereal speed.  The Philips MB01 motors with 50:1 Mclennan gearbox should be able to handle 16.6RPM at a decent torque to achieve the 0.333RPM required for the worm drive of the mount.
PS; I removed the stepper motor from the drawing.
http://www.ebay.co.uk/itm/111460019764?_trksid=p2060353.m2749.l2648&ssPageName=STRK%3AMEBIDX%3AIT
8" f/5 Sky-watcher 200P f=1000,  6" f/9 Ritchey-Chrétien Revelation Astro f=1370, 3.5" f/10 Meade 90 with 2" focuser mod f=900, 3.5" f/13 Maksutov-Cassergrain f=1200...  Heavy Duty EQ est-60lb payload.  iOptron Minitower v2, Skywatcher SupaTrak, and a damaged EQ-3 Mount. Latest;- EQ-5 with dual drive.
Camera's;- Nikon D5000, Sony Nex5, Samsung NX2000, Altair GPCAM AR0130C, Celestron NexImage SSI

Offline jhughe22

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Re: REVAMP MY HD MOUNT
« Reply #22 on: 23:38:22, 15 May, 2016 »
EQ Mount Drive from ready made units found on Ebay.
I wanted to replace the 240v motors on my HD EQ Mount but also wanted to have a stand alone system like the EQ5 Dual Driver Kit.
After several experimental attempts to build a stepper motor driver controlfrom 555 timer and 4013 flip-flop chip circuits, which was partially functional, I had foreward and reverse control but poor speed control.
My main failure was being able to produce a decent signal to drive the stepper at the correct speeds I required (16.6RPM).  The first impulse was to use a 5 Axis CNC Breakout Board For Stepper Driver Controller, but this would require using a laptop/pc.
Another alternative was the Stepper-Bee+ which is a great little unit to use and does not require a big learning curve. Again a laptop is required.

After much searching I found the L298N Dual H Bridge Stepper Motor Driver Controller Board Arduino PIC 2A, this little unit will accept 5-12v to drive your stepper motor and if your input voltage is over 7v you can then use the onboard 5v output for other devices.  I also found a DIY Adjustable Speed Stepper Motor Driver Controller Board with Remote Control, it has a 4-6v input, 8 speeds and foreward/ reverse via button or ir remote control. I decided to use these units for the DEC side of the control unit, as the speed was not refined enough for sidereal control.
The DIY Adjustable board can generate the encoded signal which will be passed to the 12v L298N H-Bridge driver to drive my Philips MB01 (with 50:1 McLennan GBox) stepper. 

Next the RA side, and yes there was another speed controller, this unit can remember the setting you had it on, the board is cotrolled by 3 buttons and 2 jumpers(mode setting)
so by increasing or decreasing the speed to what you desire and by moving the jumper2 the board will remember the speed even after powering off the board.(yet to arrive from China)

PS: just fitted one of my Philips MB01 with 50:1 McLennan GBox to the DEC side of my mount and ran it with the L298N and variable speed remote contoller. I was able to achieve 8x speed so I should be able to get on target pretty quickly. :thumbup:  However I did not take into account the weight of this large motor and i'll need to make a couple of counter weights for the SW200P and Revelation RC6 scopes.  :duh:

John..
8" f/5 Sky-watcher 200P f=1000,  6" f/9 Ritchey-Chrétien Revelation Astro f=1370, 3.5" f/10 Meade 90 with 2" focuser mod f=900, 3.5" f/13 Maksutov-Cassergrain f=1200...  Heavy Duty EQ est-60lb payload.  iOptron Minitower v2, Skywatcher SupaTrak, and a damaged EQ-3 Mount. Latest;- EQ-5 with dual drive.
Camera's;- Nikon D5000, Sony Nex5, Samsung NX2000, Altair GPCAM AR0130C, Celestron NexImage SSI

Offline jhughe22

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Re: REVAMP MY HD MOUNT
« Reply #23 on: 13:50:19, 07 June, 2016 »
Well i've mounted the motors and built my control box (12v input with two speed controllers,).  Inside the box are two L298N Dual H Bridge Stepper Motor Driver Controller Board Arduino PIC 2A boards(ebay), mounted on the lid are the speed controllers,  One 5 volt DIY Adjustable Speed Stepper Motor Driver Controller Board with Remote Control (ebay) the other came all the way from India, with a four digit display you can pre-set your speed then press start.  This unit has a very smooth ramp up and fine control for the RA motor.  The DEC controller is a bit more basic and cheap (£2.99).  It's not a pretty build but all the parts are cheaply available and readily built, you just need to wire them together.

The RA tracking speed is great, and the DEC can be adjusted very quickly, no more waiting for the object to slowly creep up the view finder.  I was able to slowdown the DEC error by using the slowest speed in the opposite direction, it's a pity it doesn't have a 1/2 speed setting.

8" f/5 Sky-watcher 200P f=1000,  6" f/9 Ritchey-Chrétien Revelation Astro f=1370, 3.5" f/10 Meade 90 with 2" focuser mod f=900, 3.5" f/13 Maksutov-Cassergrain f=1200...  Heavy Duty EQ est-60lb payload.  iOptron Minitower v2, Skywatcher SupaTrak, and a damaged EQ-3 Mount. Latest;- EQ-5 with dual drive.
Camera's;- Nikon D5000, Sony Nex5, Samsung NX2000, Altair GPCAM AR0130C, Celestron NexImage SSI

Offline tomhow

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Re: REVAMP MY HD MOUNT
« Reply #24 on: 19:02:54, 10 June, 2016 »
Looks superb to me! You have put some life back into what looks like a good mount.  What is the maximum speed you can get out of it for slewing?

I've always liked the idea of putting the dec worm on "that side" as it works as a counterweight itself.

Looks a lot like my homemade mount.... the design of which I conspicuously pinched from Chris Heapy :)

...complete with Atitude Adjuster, before anybody takes the michael :)



Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

The Curdridge Observatory

Offline jhughe22

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Re: REVAMP MY HD MOUNT
« Reply #25 on: 09:23:57, 11 June, 2016 »
Wow, that looks like a very handsome mount Tom :urock:.  As for the speed of my mount it won't break any records and would not be a candidate for goto :no:.  Though I must figure a way to  add an altitude and azimuth adjusters.   I noticed that when I turn up the speed of the RA or DEC motors it starts missing steps, though the RA has enough humph to pull the DEC motor and 10 pound weight at sidereal speed.  God knows what kind of strain that would put on the worm drive  :ugly:.

John..
8" f/5 Sky-watcher 200P f=1000,  6" f/9 Ritchey-Chrétien Revelation Astro f=1370, 3.5" f/10 Meade 90 with 2" focuser mod f=900, 3.5" f/13 Maksutov-Cassergrain f=1200...  Heavy Duty EQ est-60lb payload.  iOptron Minitower v2, Skywatcher SupaTrak, and a damaged EQ-3 Mount. Latest;- EQ-5 with dual drive.
Camera's;- Nikon D5000, Sony Nex5, Samsung NX2000, Altair GPCAM AR0130C, Celestron NexImage SSI

 

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