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Question about the new Wild Thumper Bot — Parallax Forums

Question about the new Wild Thumper Bot

NWCCTVNWCCTV Posts: 3,629
edited 2013-04-27 18:47 in General Discussion
If there are 6 motors for this Bot, how are they all being controlled using only 2 HB-25 motor controllers?

Comments

  • SRLMSRLM Posts: 5,045
    edited 2013-04-26 00:55
    You can wire them in parallel: each side gets one HB-25.
  • NWCCTVNWCCTV Posts: 3,629
    edited 2013-04-26 02:26
    Cool. I was unaware you could do that with DC motors.
  • ercoerco Posts: 20,261
    edited 2013-04-26 10:56
    Heck, you could wire three DC motors in series or parallel and run them through one speed controller, provided it can handle the voltage & current. Stalling one motor (of three in series) might actualy be kinder (current-wise) than a single motor.
  • Heater.Heater. Posts: 21,230
    edited 2013-04-26 11:18
    Wait a minute. How does that work?

    Let's say I have three motors, driven in parallel, all facing the same mechanical load, driven by a single DC supply. Current gets shared between the three, they all do their part and life is good.

    But now, I stall one motor with an extreme load. It's stall current goes through the roof. The others have no drive anymore.

    Does not sound good. Like thermal runaway in parallel transistor circuits.
  • SRLMSRLM Posts: 5,045
    edited 2013-04-26 11:26
    Heater. wrote: »
    Wait a minute. How does that work?

    Let's say I have three motors, driven in parallel, all facing the same mechanical load, driven by a single DC supply. Current gets shared between the three, they all do their part and life is good.

    But now, I stall one motor with an extreme load. It's stall current goes through the roof. The others have no drive anymore.

    Does not sound good. Like thermal runaway in parallel transistor circuits.

    I guess that implies that the stalled motor takes all the available current, which may or may not be the case. For example, say a DC motor has a stall current of 500mA at 12volts. In that case, with an HB25 (and an adequate supply), stalled motor would be getting 500mA at 12volts. The other (non-stalled) motors would have 12volts on their terminals, and draw whatever current they need.

    The problem comes when a motor draws more current than the supply can give. In that case, the supply would turn to constant current (instead of constant voltage) and the voltage would drop until the system is in equilibrium. Even in that case, the other motors would have some voltage across their terminals.
  • NWCCTVNWCCTV Posts: 3,629
    edited 2013-04-27 18:47
    I think I need a way of convincing the wife that this is a "Must have in order to" item!!! Looks preety sweet for the price. Has anyone on the forum bought one and if so, what are you thoughts on it?
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