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Question: Off Delay Timer

Discussion in 'General Electronics Discussion' started by sowjoe, Oct 7, 2012.

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  1. sowjoe


    Oct 7, 2012
    Hello everyone,

    I know nothing when it comes to electronics, please be patient with me.

    I'm looking for an adjustable off delay timer that can delay multiple (2 or 3) small dc motors (cordless drill motors).

    Here is what I want to do....

    Motor A & B - both motors turn on (run) when a button is pressed.

    Motor A runs for 5 seconds then shuts off

    Motor B runs for 5 seconds at 60 rpm's then powers up to 100 rpm's after 5 seconds and runs for a total of 10 seconds then shuts off.

    I'm looking for something simple and inexpensive.


    I've seen some traffic light off delay timers on Youtube that may work, for example....

    Green light turns on = Motor A & B turn on (run for 5 seconds)

    Green light turns off = Motor A & B turn off

    Yellow light turns on = Motor B turns on (runs at a higher speed), runs for 5 seconds then shuts off

    Can you point me in the right direction on where I can purchase the above or maybe build it myself?.... again, I know nothing about electronics but I am willing to learn. The motors are 2 - 14.4 dc Dewalt drill motors.

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The timing is pretty simple, the speed control decidedly less so.

    Are they under constant load?
  3. sowjoe


    Oct 7, 2012
    constant load? I don't understand your question. If you're asking "are the motor's under constant load when they are turned on" then the answer would be, "yes."

    I was thinking on the speed control.... cordless drill motors have 2 speeds (at least the 14.4v dewalt drill I have does). So when both A & B motors shut off the first time and B motor starts up again, I could somehow switch the 2nd start-up of motor B to a higher voltage.... does that make sense?

    The switch on the Dewalt drill motor has 2 settings. If the switch is pressed a little way the motor runs at a slower speed. When the switch is pressed further, the motor will kick in to a higher speed. I'm assuming the first position of the switch engages lets say 4 of the 8 batteries (I don't know how many batteries are in a 14.4 dewalt drill, I just guessing) and when the switch is pressed further it engages the remaining 4 for a total of 8.

    Again, I don't know much about this stuff but I am a quick learner. Does that answer your question?

    Thanks Steve
  4. Merlin3189


    Aug 4, 2011
    So your 3 states are:
    1:Motor A on and Motor B on at 60rpm
    2:Motor B on at 100rpm
    with the 2 on states lasting 5 sec each and the off state being the quiescent state.
    So two timers with the first triggered by the start event and the second triggered by the end of the first timer.
    First output switches power to motor A and switches, say, 6V to motor B controller.
    Second output switches 10V to motor B controller.

    To an old timer like me, that's a PB switch, two 555's, two change over relays (one 2-pole) and a motor contoller, but I expect you'd replace relays with solid state these days.
    As for the motor controller, Steve sums that up nicely. I think the general idea would be to have a small resistor (maybe just the supply cable) in series with the motor, sense the Voltage across it and add a multiple of it (motor resistance / sense resistor) to the applied Voltage. I guess that would work ok with this motor having lots of friction and not much inertia, but you can get into complicated issues of damping and response times with motor controls. If the speeds are purely nominal, then maybe just applying two fixed Voltages is ok and you don't need to regulate at all.
  5. sowjoe


    Oct 7, 2012
    Hey Merlin,

    The 3 states could be...

    1) Motor A & B on (motor B running at a slow speed... 60 rpm's or so for 5 seconds)
    2) Motor A turns off and Motor B turns off
    3) Motor B turns on again at a higher rpm and runs for 5 seconds then shuts off

    Here's an idea I had....

    My idea of controlling the speeds of the motor is by using different battery packs. I'm thinking if the motor turns at 500 rpm's using a full pack of 12 batteries (14.4v), I can slow down the motor to 250 rpm's by using 6 batteries. To switch between the 7.2v and the 14.4v I can insert some kind of relay. If 7.2v is too much (rpm too high) I can split that in half and use 3 batteries..... what do you think?

    I think I might have to modify my design by use only one motor instead of 2 to make things easier.

  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Presumably if the existing motors are sufficiently controlled already, it would be a case of applying power to the motors the same way the drill does. This may mean using a control board that is inside the drill, or perhaps there are multiple windings, but it doesn't mater, you just have to figure out what the switch does and duplicate it.

    Since you're duplicating switched, and because the speed is so slow, relays are a good simple option.

    As suggested, a couple of 555 timers set up as monostables would work, however there are several people who have suggested in similar threads that time delay relays could be used.

    It really depends on how mush effort you want to put into this as opposed to the $$$ you're prepared to pay.
  7. sowjoe


    Oct 7, 2012
    I was thinking....

    I could run an off delay timer through a pot to get the slow speed for 5 seconds. Then install an "on delay timer" that turns on after a 5 second delay, runs wide open for 5 seconds then turns off. That might work.

    Now all I have to do is figure out where to get the parts and build the thing.

    What do you think?
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