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Motor identification

Discussion in 'Sensors and Actuators' started by autoq, Feb 18, 2017.

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  1. autoq

    autoq

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    Feb 18, 2017
    I am trying to identify (and then drive via an Arduino or Pi) a motor in my (Meade) telescope mount. The manufacturer "support" people refuse to send me any technical information. I was originally thinking that this is probably a stepper motor, but I am not sure now.
    I have linked 2 images. The first shows the motor with wires connected , the other is without the connector attached.
    The images show the 6 wires coming off the motor. 2 at the side (blue and orange) and 4 in the middle.
    There is 0 resistance between the Orange and Blue wires. From the pins on image2 ( Pin 1 is on the left, 4 is on the right), the resistance between the other pins is as follows :-
    1 to 4 1500 Ω
    1 to 3 6000 Ω
    1 to 2 50K Ω

    2 to 3 2500 Ω
    3 to 4 1500 Ω

    There is no connection Blue or the Orange and any of the 4 pins (which is why I now think that this is not a Stepper motor).
    Any suggestions as to what to try in order to get this motor to turn ..... ?

    Many thanks for your time !

    Rodney
     
  2. Minder

    Minder

    3,066
    657
    Apr 24, 2015
    A dual winding four lead stepper motor is a Bi-polar version but would normally have two identical but separate winding's.
    If you could drop the motor off and try turning the shaft, an indent when not powered usually indicates a stepper.
    The three on the side may be a zero or home position indicator.
    M.
     
    hevans1944 likes this.
  3. hevans1944

    hevans1944 Hop - AC8NS

    4,596
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    Jun 21, 2012
    It looks like a permanent-magnet (PM) DC motor with either an optical encoder or a tachometer attached to the end. Is there a gear-reduction box between the motor shaft and the telescope mount? Is this an alt-az mount or an equatorlial mount? You should be able to detach the blue and orange wires and apply a reversible DC voltage where they connected to the motor to get the motor to run. Do you have any idea what voltage that might be? A variable-output bench power supply capable of supplying 0 to 24 V DC at a few amperes should be sufficient to energize the motor. Does the original motor controller work? If so, you could measure the motor supply voltage on the blue and orange wires with the motor running, which may be a variable voltage depending on motor speed. A LOT more information about what you are trying to DO would be helpful.
     
  4. autoq

    autoq

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    Feb 18, 2017
    Thanks for the suggestions.- and so quick also. I didn't want to bore anyone with details of my little project, but FWIW, the telescope (It is an Alt-aAz mount.) was working very well. It has a lot of electronics in it which e.g. automatically positions/aligns and guides the telescope . However, the electronics have given up and I cannot refresh the firmware. (the SD card slot is broken and I can't find a sensible affordable replacement ) . The telescope itself is as good as built into the mount and so not useable if the electronics aren't playing. (lousy design).
    The motors/gears are in decent conditiion, so all I want to do is really apply a voltage/signal to the appropriate part of the motor in an appropirate manner, and e.g. press a button to move the mount left/right or (there are two motors which I am assuming are the same) up/down.
    The mount takes 8x1.5V batteries so implying that the motor will be a max of 12V, but I'm thinking more like 9.
    I am now thinking of applying the voltage as suggested directly to the blue/orange wires ... will let you know when I get round to it ... many thanks again ...
     
  5. hevans1944

    hevans1944 Hop - AC8NS

    4,596
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    Jun 21, 2012
    This could be a really fun project to "reverse engineer" the motor control circuits for your alt-az mount. Can you provide a model number for the Meade telescope? I am sure there are Meade blogs and forums where you can also get a lot more help.

    I have been fascinated with optics and telescopes for many years, but the "seeing" in Dayton, OH, where I had lived since 1962 before retiring to Venice, FL last year, was terrible. That didn't stop amateurs in the area from building and buying some pretty sophisticated telescopes and forming astronomy clubs, but you generally had to go pretty far out in the country away form city light pollution to do any serious work. I never felt I could afford to make the investment in a decent telescope that would be marginal at worst, and inconvenient to transport and use at best. But I am amazed at the "seeing" outside my house in South Venice. Not amazed enough to actually purchase a telescope, but I do plan to find out if there are any astronomy clubs nearby.

    I agree with your assessment of the motor voltage. If those eight cells are "D"-sized alkaline cells, they should be able to drive a DC motor for several hours if PWM is used to control the slewing and tracking speed of the two motors. When I first became interested in astronomy, all telescopes were fitted with awkward equatorial mounts and required only a single motor drive, usually a synchronous AC clock motor running from either the power-line frequency or a crystal-controlled oscillator. Depending on a star's altitude, that was good enough for several hours of long-exposure photography or spectroscopy on an integrating image array. The advent of inexpensive microprocessors spurred a revolution in compact alt-az mounts, and go-to programming capability for casual visual star gazing or terrestrial spying.

    Not sure if your alt-az drives are good enough for long-exposure astro-photography of deep space objects, but that would depend on the mechanics and whether using film or an imaging array. Assuming those are optical encoders mounted on the motors, you should be able to program an Arduino or a RPi to accurately track at least planets and other solar system objects bright enough to capture with a few minutes of exposure. It will require pulse-width modulation of the motor current to control the tracking speed independently on each axis, even if all you want to do is push a button for alt-az telescope position changes. For astronomy you will need some spiffy software, but there is probably plenty of that in the public domain and free to download. It all depends on what you want to DO as to where you go from here. Please elaborate with all the details. Those who are bored reading them will just move on. At the most, a few zillion electrons will be inconvenienced, but there is plenty more where they came from.
     
    autoq likes this.
  6. autoq

    autoq

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    Feb 18, 2017
    So the telescope is a Meade ETX LS (6") . You're right that an Equitorial mount only needs 1 motor as it tracks the rotation of the earth - which also makes it better for long exposure astrophotography, however the Alt-Az is easier to setup (you don't need to align it with the North star).
    I only have some time at weekends to look at this and so it may take a wee while to make progress... I will check back when I am in a position to connect up the motor ....
     
  7. hevans1944

    hevans1944 Hop - AC8NS

    4,596
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    Jun 21, 2012
    Wow! That's a pretty nice telescope, although the supporting hardware has had some mixed reviews. Meade seems not at all inclined to help the amateur with repairs or modifications. So, assuming the electronics is toast or beyond cost-effective (or affordable) repair, your only hope is to drive the two motors from an external controller. Should be a "piece of cake" for the advanced electronics hobbiest.

    I am going to guess that the low resistance you measured is for what appears to be the motor commutator. You do NOT want to apply steady-state DC to the motor. It will probably run waaay too fast and draw waaay to much current if you apply nine to twelve volts DC directly to the motor. And much lower voltages may not provide enough torque to reliably run the motor. You can purchase PWM controllers on eBay for about five bux or so to let you find out how the motor responds to PWM control. Eventually you probably want to do the PWM control yourself with any of a variety of microprocessors, some with the capability "built in" because it is so popular for small PM DC motor controllers.

    Meanwhile, you and others here on EP can try to find out whether those are optical encoders attached to the motor. An alt-az mount is pretty much useless without position feedback to let you know how to get from where you are to where you want to go. If I am not mistaken, they require you to initialize their position information by aiming the telescope at one or two known guide stars visible above the horizon. Once that position is "memorized" by the software, it is easy to slew or "go to" any other position provided you don't move the telescope support... tripod, orange crate, cinder blocks or whatever.
     
  8. autoq

    autoq

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    Feb 18, 2017
    So , I just hard wired a 9v power source to the motor and it turned. Then I switched the connections and it turned back. Yay .
    I have now a well over-engineered raspberry Pi /breadboard(with leds and buttons)/motor driver/setup with wires/resistors everwhere. .. along with some hand cranked Python code, and can now turn the motor back and forward , according to the button which I press, etc. However its a bit/(very) unweildy and so I need to tidy the engineering and get down with some soldering.... it will be another few weeks .......
     
  9. Walter Hynson

    Walter Hynson

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    Apr 10, 2021
    The motors are DC powered 9 VDC with a encoder wheel which tells the computer the telescope Alti/Az location,I have a EXT 80 and am testing a arduino with PWM controller and a IMU 9Dof to tell the arduino and user via LCD the user entered target via 12 key keypad and the output from the IMU the arduino will send either wide or narrow pulses to drive the motors until the entered target data and the output from the IMU matches within 5-8 degrees ,I want Stellarium to update the target location every 15 sec or so to keep the scope on target,one thing i really want to do is replace those cheap DC motors with steppers and get rid of all the Meade crap.
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    @Walter Hynson : Did you recognize that this is a Zombie thread from 2017?
     
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