Hi all.
How would i go about sending a quick signal to move a dc motor at full speed for 1second? Basicly. I have a stepper motor that slowly pulls cinefilm through a flatbed scanner. But after a while i have an excess of film just bunching up. I need the dc motor to pulse slowly as to wind the film back on to a reel without pulling the film and breaking it.
Dave
Do you have this DC motor? If so, what are the specs?
If you need to run the motor both forward and reverse, you will need an H-bridge motor driver shield. If you only need one direction, a MOSFET will do the job. You can still you an H-bridge, but not really necessary. It depends on your skill/comfort level.
Or a slipping clutch?
I would suggest trying a PWM signal with a very low mark-to-space ratio, in other words, analogWrite(pin, 1); or some other low value. Increase the value slowly until the motor takes up the slack film. If you run the motor at full speed for one second, it will build up momentum that could damage the film.
Pulsing may not produce the wanted results, but a mechanical gearing will always do the job!
Thank you all for your reply's.
I can't really afford to buy anymore stuff for this project. Was hoping that there would be a software solution. The DC Motor is
200:1 Plastic Gearmotor
and this is the driver
l298n motor driver
if i move the dc motor slowly via PWM i need to set it to 35 just to get it 2 move but boy does it make a horrible high pitch whine (Like my wife lol).
thank you all again for replying.
Dave
That can probably be fixed. What Arduino are you using? And which PWM pin?
For Uno/Nano pin 9 or 10, try adding this to setup():
TCCR1B = 0x01;
You might have to adjust analogWrite() value again.
Wow, that did the trick. What does it do? Frequency change of the PWM?
Uno yes.
Analogue multi track recorders have a similar problem if you allowed them to just use one motor.
The answer is to have a the second motor that has a weak current pulling the motor back in the opposite direction, to maintain tape tension. This works for normal play and fast forward/rewind, without having to utilise mechanical slipping clutches, which wear out and vary over time.
Other methods used on cheaper machines has a band of felt on a spring loaded metal band, to create tension.
Now thats a smart idea. Wouldnt work with a 200:1 geared motor tho im guessing.
Which is whats currently running the takeup real
Also. Wouldnt have the motor constantly powered but not moving burn out the motor?
Yes. It's still making a horrible high pitch whine. Your dog/cat may still be able to hear it.
Haha.
Yes well a 200:1 take up reel motor is one thing, but a tension motor would of course be required and no it wouldn't burn out the motor, given the holding current is very weak.
Think of it as a device for generating a weak magnetic field rather than it trying to be a motor being pulled backward. The current to do this is very low.
Analogue recorders however do work differently, given the take up spool also has a weak current to keep the tension between the drive roller and the take up spool and the tape is pulled by a pinch(drive) roller at a constant speed.
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