Motor control timing circuit question

Discussion in 'Digital Circuit Design' started by ronfinlay, Oct 8, 2016.

  1. ronfinlay

    Thread Starter New Member

    Oct 8, 2016
    3
    0
    Hi AAC folks

    New to the forum tonight. Try to develop a circuit which produces a drive for a relay, using a 555. The relay drives a motor. The motor needs to rotate 1/2 turn, stop for 2 seconds and turn 1/2 turn to the rest position, then wait until triggered to start again. I have a pushbutton to start things off. Thinking of using micro switches to detect final stop/start position (like a garage door opener, which has two limits switches, upper and lower). So, the sequence of event is as follows. Push the button. In case that pulse is too short and the motor doesn't move far enough to release the micro switch (open to closed), I was thinking of a 555 one-shot to bypass the micro switch for 1/2 second, but it needs to drive a relay because the motor draws 1 amp. So, relay contacts in parallel with micro switch's NO contacts in case they don't close as fast as the push button signal lasts. OK, motor's turning and gets to 180 degrees. Need to stop for 2 seconds. Upper limit microswitch interrupts current. If I put this micro while in series with the motor on the low side, I can use the contacts to generate a 5->0V signal, triggering another 555 monostable to generate a 2 second high, and when it drops to 0V, pull another relay to bypass the upper limit microswitch to get things going again. Finally, at 360 degrees, the lower limit micro switch kicks in and cuts the current. Now, to start over, push the button, start the motor, trigger the 555 to ensure a clean start.

    All you smarter than me folks out there... does this sound right or is there a better way? All I need is the motor to turn in response to a push button, turn once, but stop half way round and wait for 2 seconds.

    I was thinking of triggering a 1 of 16 decoder chip clocking at 8 Hz, and only connecting the first 2 and last 2 outputs, so the 0's in the middle section would simply be unable to drive the relay (just time passing by). So my output would be 0,0,1,1,1,1,1,1,1,1,1,1,1,1,0,0, so the motor turns, stops, turns, and I can always adjust the number of outputs or clock to match motor speed to mechanical load. I still need the micro to ensure end of cycle is mechanically correct, and push button to start it all.

    I would appreciate any thoughts on this. I need to make this thing tomorrow, or even tonight !!! Thanks.
    Ron
     
  2. tranzz4md

    Member

    Apr 10, 2015
    139
    27
    Tell us something about the motor, and how close to those positions you need to be, and your load. (High inertia?)
     
  3. ronfinlay

    Thread Starter New Member

    Oct 8, 2016
    3
    0
    Wow. Thanks for being there. It's a small geared motor, about 360:1 from a film camera winder, and I've seen lots on robotics websites just like it. 3 mm shaft, 60 rpm at 5V (1 rev/second), although it's a 6 V DC motor. I've still got to connect to a crank disc and connecting rod to move the load, with is about 5 pounds, through 1/2" vertical movement. If the motor's too weak, I can gear it down, and put all the stop start micro switches on the final output. I was thinking of putting a tab on a block to catch the upper and lower limit micros if need be.

    Just made a cam, but in one revolution, it's got to rise 1/2" in 90 degrees, dwell for 180 and back down in 90 degrees, assuming 4:1 gearing, for a total cycle time of 4 seconds. We need this to get the 2 second dwell, which is the mechanical cam dwell version of electrically stopping the motor for 2 seconds.

    I'm still thinking electrical control is best. Thanks for your thoughts.
    Ron
     
  4. tranzz4md

    Member

    Apr 10, 2015
    139
    27
    I like the cam and dwell achieved at the load, by use of that mechanism. I'd sense that load position, or... make a cam to trigger your microswitch/prox/magnetic switch, whatever. You're best stopping and starting that cycle mid-dwell, or just before the cam lifts the load.
     
  5. ronfinlay

    Thread Starter New Member

    Oct 8, 2016
    3
    0
    Thanks. I just figured out the circuitry for the 555, two micro limit switches and one spst relay. Funny, the upper limit micro goes to the bottom of the schematic (switches ground so it can trigger the 555) and the lower limit micro goes at the top so it can switch +5 to power the relay if the 555 output is low. Gotta go through it a few times and tomorrow make a cam version as well. Thanks for your kindness.
     
  6. tranzz4md

    Member

    Apr 10, 2015
    139
    27
    Actually, a 2 or even 3 segment sliding "cam" on that camshaft can get you a very easily adjustable action and load-move delay for motor start/run stabilization. You can use the 555 triggered by that cam position if you have a substantial variation on cycle to cycle load, but since you'll stop or reset your cycle at that "load lowered" position a varying armature/mechanism stop time will be within that variable stop-to-restart time.

    Sounds like you're cruising! Tear it up man!
     
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