Programmable fine grain motor control

Discussion in 'The Projects Forum' started by Greg_R, Mar 30, 2010.

  1. Greg_R

    Thread Starter Member

    May 5, 2009
    11
    0
    Hi everyone,
    I have a fairly complex project in mind but I want to start small and slowly add features to my system. The project is to design and build a 4-way screen masking system for a home theater. Right now one of these systems costs about $10k (not counting the screen!) so I figure I can build something for much less and publish the design for other DIYers to use. My general idea is to have a PLC or microcontroller actuate a motor so it will spin a rod (opening/closing a curtain) until a certain point is reached. The curtain/masking mechanicals are already thought out... I just need a control system for the motors. Limit switches would be employed to prevent over-excursion of the curtain. However, the curtain would need to be stopped in various positions, based on the aspect ratio of the program that's being watched. This would consist of a table in a EEPROM (aspect ratio of 16:9 go to position W,X,Y,Z; 4:3 have each curtain go to a different position). User control would be done via RF or IR remote control and would also be capable of storing settings into the EEPROM.

    Inputs:
    - Remote control, sends a memory lookup location -or- "bump" commands for each motor for fine adjustment
    - limit switches on each curtain to prevent over extension
    - Motor feedback?

    Outputs:
    - Control signals to control a motor or commands send to stepper motor


    Questions:
    - Are there 1/4HP or below stepper motors? I am having trouble finding a motor solution that is relatively inexpensive (<$100 per unit). Are there cheaper options (not necessarily a stepper motor) that will provide the functionality I need? The motor will need to 'hold' its position after a move is completed.
    - I had been looking at the 'Click' PLC which seemed fairly attractive from a cost and functionality standpoint. However, I am more comfortable with PIC programming (vs 'ladder' programs) and I think a PIC + EEPROM may be more suitable (in terms of voltages being used & intended applications). Thoughts?

    Once I determine my controller and motor solution I'll ask more questions about recommended sensors, etc. My plan is to breadboard a simple circuit with the controller & motor and get that working. Once that's done I'll add additional motors and the remote capability.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    There most certainly are. What is being moved that might take that kind of power? Can you quantify the size of the thing being moved, how far it must be moved, and how fast it must move from one position to the next?
     
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    A small geared motor should be OK, or even a large radio control servo motor modified for continuous operation.

    For positional feedback, use a multi-turn potentiometer. 10 & 15 turn are standard parts.
     
  4. Greg_R

    Thread Starter Member

    May 5, 2009
    11
    0
    The masking system is essentially 4 sets of motorized blinds (one for each edge: left, right, top & bottom). The rod that rolls the blind on & off will be between 1" and 1.5" in diameter and will be mounted on bearings on each end. I envision the motor directly driving the end of this pipe/rod. If I were to do that, I would need ~50 turns from the motor (to get 50 x pi x 1 effective travel on each screen). Accuracy would need to be a linear 1/16" to 1/32" on the screen, so ~100 steps per complete rotation. If I were to use gearing then the number of turns could be less but the torque requirements would go up.

    In terms of power, the worst case scenario would be for the top mask which has to fight gravity (weight of the extended screen), a light tensioning mechanism, & the inertia of getting the roller rolling. Some DIY versions have used modified antenna mast rotators but slightly more power would be preferred.

    In terms of speed, it would be nice to achieve 1000-2000 RPM, 600 RPM or below would start to get slow. The goal is to fully open the masking in < 5 seconds, anything beyond that would be slow and anything under 1.5 seconds may stress the mechanical rolling mechanism (bounce, spring back, etc.).
     
  5. Greg_R

    Thread Starter Member

    May 5, 2009
    11
    0
    Oh yes, the rod could be as long as 15'+ wide and fairly heavy but the motor is only trying to spin the rod on bearings. It is easy to spin using finger pressure.

    This link shows the mechanical solution and may visually explain what I'm trying to do. The system on the 1st page works very well manually. My goal is to automate the thing via motors & controller.
     
  6. Greg_R

    Thread Starter Member

    May 5, 2009
    11
    0
    Some people are using this antenna mast rotator by modifying the internal gear ratio and using a large pulley (thus getting the correct RPM on the rod). Unfortunately this is IR-only and I would like to design a solution with various input methods (RS-232, IR, RF, etc.).
     
  7. Greg_R

    Thread Starter Member

    May 5, 2009
    11
    0
    Does each motor require it's own motor controller (or are there controllers capable of controlling multiple motors at once)? There will be a central board and then some wiring to each motor. At what point in the circuit should I place the 'long' (10') wires? Between the motor controller and motor or between the microcontroller and motor control?
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    I might suggest that small (3 - 4") speakers mounted close to the aperture of the projector could effectively crop the presentation on the screen.

    You have to fix a post to the center of the cone to carry the shutter. It looks as if a movement of a fraction of an inch could do the trick.

    Even a few hobby servos carrying a shutter that turns in and out of the edge of the projection could work.
     
  9. Greg_R

    Thread Starter Member

    May 5, 2009
    11
    0
    The image is automatically cropped & scaled by the projector or scaler. An auto-masker is used to place black cloth right up against the edge of the image. A common issue with digital projectors is that 'black' is not really black (full off / no light hitting the screen). Masking covers up the edges and gives the human eye a reference to a darker black. This has the effect of making the image on the screen appear brighter (trick of the eye).

    This link talks about the benefits of masking in a little more detail. I am essentially trying to copy the functionality of this system (but with $10k+ less cost).
     
  10. Greg_R

    Thread Starter Member

    May 5, 2009
    11
    0
    This is exactly what I'm trying to do except the shutters are 'large' (full width of a 10'+ wide screen) and there is a shutter for each screen edge. The shutter rollers, tracks, and material are a custom DIY design (see post #5 for a link describing that setup)... I am just trying to create a very flexible automation solution for driving the shutters.

    Thanks for the help so far, I really appreciate the feedback.
     
  11. Greg_R

    Thread Starter Member

    May 5, 2009
    11
    0
    Last edited: Mar 31, 2010
  12. Greg_R

    Thread Starter Member

    May 5, 2009
    11
    0
    Alberto, are you saying I should have 10N-m at the roller or at the motor output. In other words, should I be looking for 10N-m or a ~3.3N-m motor? 10N-m sounds pretty big (compared to window shade motors, etc.).
     
  13. master2000

    New Member

    Apr 1, 2010
    1
    0
    i looking to make the 2 motor mask
    http://www.smxscreen.com/pro-mask-curv-masking.html

    i don't much electronic but i see you work is great i lookin to this site http://www.01mech.com/ they make the servo detect the info of the rotation and you cand connect direct to the controller not need interface for the motor that is great an is precise look this videos.

    http://www.youtube.com/user/antona99#p/u/2/1fUwPSn32T8
    http://www.youtube.com/user/antona99#p/u/1/-z0Giro4R7M
    http://www.youtube.com/user/antona99#p/u/0/8jajnIBX2cU

    and this is the servo there i buy is powerful i can't stooped
    http://cgi.ebay.com/2-x-MG995-Hi-Sp...Control_Parts_Accessories?hash=item230646a257

    if you make it work you can make the board available for diy like me well be great :) keep looking to make it work.

    And i make the curved screen i recomed you make it you no believe after you see yourself is like you are inside of the movie i post in avs the making of the screen is make of wood 2.35 8' diagonal 30' radius curved.
     
    Last edited: Apr 1, 2010
Loading...