pwm speed control

Discussion in 'Electrical & Radio' started by Nick Park, Aug 17, 2009.

  1. Nick Park

    Nick Park Member

    Joined:
    Jun 16, 2009
    Posts:
    97
    Ive used a simple PWM speed control circuit (this one below in fact) and found something very interesting.
    The batteries last much longer than ever and the speed is 28 (for my HMS Erin) and not 27 or 29 or decided by using different sizes of prop or by using spinners.
    The pwm switches on at a certain frequency and off at a certain frequency. thus, the motors speed is regulated. the most interesting thing is that the motor during it's ON phase is at full power, making a speed pre-regulated, which is not without its full power performance.
    Due to the moments of being "OFF" there is no usage of the battery and Ive found that 1hour with the motor directly connected used up most of a 7.2AH battery equalled 1hr with a 2.3AH battery using a pwm.
    The weight difference is important, but the best thing is the difference in space taken by a battery.
    The circuit is simple to make and with 2 500 motors never got hot, even in the french sunshine.
    [​IMG]
     
  2. jadfer

    jadfer Well-Known Member

    Joined:
    Mar 29, 2008
    Posts:
    1,576
    Location:
    Houston, TX
    Any pictures?
     
  3. Nick Park

    Nick Park Member

    Joined:
    Jun 16, 2009
    Posts:
    97
    sure, its about the size of a 2 euro coin.. 2x3 cms
    [​IMG]
     
  4. mike5334

    mike5334 Well-Known Member

    Joined:
    Aug 21, 2007
    Posts:
    1,877
    Location:
    Mississippi
    AKA an Electronic Speed Control. :)

    Good job actually making one. That takes skills and knowledge most people like me do not have.
     
  5. rarena

    rarena Well-Known Member

    Joined:
    Jan 18, 2008
    Posts:
    1,221
    Wow, very interesting. perhaps the next time I order electronics......
     
  6. Nick Park

    Nick Park Member

    Joined:
    Jun 16, 2009
    Posts:
    97
    Its true that one has to learn yet another skill, in order to build a speed controller. But... making a battleship that shoots ball bearings (as we do) uses a great number of disciplines and sklills, from cutting and forming wood and plastic and metal, understanding gas movements are just 2 examples.
    the parts cost me (here in france) 10€, about 14 dollars (about 700 dollars australian lol)
    and the time I took to solder all the bits was half an hour. but any person can build it in an evening.
    Ill take some fotos of the back of the board and make a scehatic of ther vero board so it can be even simpler to do.
     
  7. warspiteIRC

    warspiteIRC RIP

    Joined:
    Aug 17, 2008
    Posts:
    756
    Location:
    Annapolis, MD
    how much amps can the circuit handle? Fast Gun motors use more current than big guns.
     
  8. rarena

    rarena Well-Known Member

    Joined:
    Jan 18, 2008
    Posts:
    1,221
    The circuit says 2 amps max and you're running two 500's, not even hot. Fast gun does draw more amps, direct or gear drive? Mine jumped when I went direct. I look forward to the picts.
     
  9. Nick Park

    Nick Park Member

    Joined:
    Jun 16, 2009
    Posts:
    97
    2 amps max is an iteresting answer.
    in fact the motors never draw full current asd they are "ON" for some of the time and "OFF" for the rest of the time.
    I couldnt find the Transistor required and so I took an equivalent which had the same properties, but handles 5 Amps.
    In general, a PWM cct runs at 90 to 98 percent efficiency, and at the voltage required.
    I used a TIP40 transistor just to be safe and WITH a heatsink.
    theory for those who want to know more can be found here....
    http://pcbheaven.com/wikipages/PWM_Modulation/
     
  10. wrenow

    wrenow RIP

    Joined:
    Jul 30, 2007
    Posts:
    439
    Am I correct that what you have is a single sped PWM control with no reverse?

    Cheers,
     
  11. rarena

    rarena Well-Known Member

    Joined:
    Jan 18, 2008
    Posts:
    1,221
    I got the 2 amps from the drawing. Right by the motor + and - it says two amps max.
    direct drive or gears???
     
  12. wrenow

    wrenow RIP

    Joined:
    Jul 30, 2007
    Posts:
    439
    Another question. You say 2 500 motors. Are you talking, say 500TB (small motors marketed by Tamiya as the Solar Motor 02) that dray one amp or less, even at full stall?

    Or something more like a 540, 545, 550, or 555? A 550, in particular, can draw between 80-90A at full stall even though they may only draw 1-2A on the bench.

    The stall draw for some common 6v+ motors in the 5XX series other than the 500TB
    540RH, 20.4-37A depending on model
    545SH, 45A
    550PC, 70A
    550VC, 85A yes, 85A, not 8.5A
    555PC, 9.9A
    555PX, 7A

    Are you planning on waterproofing the circuit?

    What happens when the variable resister (potentiometer) gets wet and the resistance changes?

    And, while this PWM unit is adjustable, only on the bench, correct? Not from the radio like a regular ESC?

    Cheers,
     
  13. warspiteIRC

    warspiteIRC RIP

    Joined:
    Aug 17, 2008
    Posts:
    756
    Location:
    Annapolis, MD
    If you put it before a MAG speed control, you can control the top speed and let the Mag do the reversing. The pot is set for full speed (for the ship).

    Marty
     
  14. warspiteIRC

    warspiteIRC RIP

    Joined:
    Aug 17, 2008
    Posts:
    756
    Location:
    Annapolis, MD
    if you want just forward then attach the pot to a servo. Some clubs used to not allow reverse, don't know if that is still true.

    Marty
     
  15. crzyhawk

    crzyhawk Well-Known Member

    Joined:
    Feb 25, 2007
    Posts:
    2,306
    Location:
    Alexandria, VA
    That's brilliant Marty. I can't believe I didnt think of that with the 50% reverse speed controls I have. I just might have to throw a MAG into the Belleau Wood!
     
  16. wrenow

    wrenow RIP

    Joined:
    Jul 30, 2007
    Posts:
    439
    Both excellent points, Marty, but then either option introduces mechanical (the servo) failure points, not to mention taking up more space/weight, etc.. Still have the issue with moisture in the control pot, of course.

    A waterproof ESC eliminates all the mechanical and servo issues, of course, and many are even more compact than the circuit shown here. And, if the motors only draw a max of 1A each, the Vex Robotics Motor Controller (ESC) is only $10 for a fully reversable ES that runs directly off the RX servo bus (no separate wiring for the motor power).

    Cheers,
     
  17. warspiteIRC

    warspiteIRC RIP

    Joined:
    Aug 17, 2008
    Posts:
    756
    Location:
    Annapolis, MD
    not necesarily, Wreno. Mag switch with a team delta board (rce220) does not use a servo. ;^}

    Marty
     
  18. rarena

    rarena Well-Known Member

    Joined:
    Jan 18, 2008
    Posts:
    1,221
    I love it when the minds meet and talk electronics!!!
     
  19. Kotori87

    Kotori87 Well-Known Member

    Joined:
    Nov 8, 2006
    Posts:
    3,522
    As long as you can keep up with the "tech talk". I'm doing good so far, but not sure for how much longer...
     
  20. wrenow

    wrenow RIP

    Joined:
    Jul 30, 2007
    Posts:
    439
    True, Marty but you mentioned a MAG switch (which uses a servo as originally designed and usually implemented from what I have seen).:) Personally, I have never seen a reversing MAG switch made from a Team Delta. Is it done?
    And using s servo to control the pot is still using a servo....... Can't do that with a Team Delta (OK you could use a passle of them with resistor bridges to get the effect, I guess).

    BTW, as for the reverse, it is important to look at local club rules. The club I bleong to, NTXBG, does not allow combat reverse. You can use reverse throttle to stop, or to back off of a grounding, or some other obvious problems (trying to demoss), and in port. If it is not obvious, you usually announce and see fif there are any objections.
    But, you do not reverse direction in battle to better your position or get out of a tough spot. Makes you plan a bit further ahead, and makes a lack of situational awareness a bit more fatal.
    It is so ingrained in us, in fact, that some have been known to feel funny using reverse and avoid it in the Texas Cage Match, where all the ships are trapped in port for the battle, with little maneuvering room, and reverse is allowed at will.
    Some clubs have no such restrictions.