What should I use for blocking and unblocking a video beam coming out of a video projector?
I have this in my mind right now:
Rotate 90 degrees to block the beam, rotate -90 degrees to unblock.
I have bought both a 5v BYJ48 Stepper Motor and a hobby servo motor from eBay.
Is using a motor for this a good idea?
Maybe there is something readily available which will do this job better?
One issue I can think of is the "blocker" slowly falling out of place and letting some of the video beam pass through, because the motor rotating 90.4 one time and then say 90.3 the other time, after 100 operations it will really fall out of place.
Yes, I'm not very experienced in electronics.
Maybe a simple RC servo will do the job, depends on how fast it needs to move. Be aware the shutter may get warm/hot very quickly if shuttering for a long time.
Why don't you have a mechanical stop positioned where you want the blocking vane to stop.
Put a switch on it so you know when it is in position, also use a stop and switch for the open position.
Stepper would work well.
With a stepper you can program a brake/hold mode if you like , but a physical stop would be better.
I second this. A standard RC servo should swing enough to close/open a shutter and you will need no extra stepper driver hardware. The problem will probably be isolating the motor shaft from the shutter to reduce heat transfer or cooling it when closed.
snklvl100:
Any particular reason to go with servo instead of stepper? I don't mind both, just curious.
Servo only needs the servo, power for it (don't power it directly from the Arduino 5V power pin) and one extra pin to control it. All the positioning and repeatability is built into the servo.
Stepper motor also needs a power source, a stepper driver and a switch to determine home position.
Okay.
Should I rely on the servo angle not changing slightly over time and just rotating 90 degrees and -90 degrees, or should I still use two switches on each ''end'' to prevent over and undershooting, if thats the correct term?
Alo, if power is suddenly shut down, how can you make a servo return (rotate) to 'home' position? Or you can't and will need switches for that?
snklvl100:
Should I rely on the servo angle not changing slightly over time and just rotating 90 degrees and -90 degrees, or should I still use two switches on each ''end'' to prevent over and undershooting, if thats the correct term?
Alo, if power is suddenly shut down, how can you make a servo return (rotate) to 'home' position? Or you can't and will need switches for that?
No need for switches. The servo contains it's own feedback to know what angle it is at (even after power down). Look at Servo library and you will see you move the servo by specifying the angle needed.
One last thing I'm worried about which I mentioned before:
Is there some ''overshoot'' or ''undershoot'' when rotating these rc servos? I mean for example rotating 90.4 degrees one time, then 89.4 another time instead of 90. I'm asking because if this is the case, after "prolonged" use the angle might be so off that the blocker won't be bloking all the beam anymore.
If the electronics inside the servo motor housing takes care of this and even if tiny overshooting /undershooting exists but they won't build up, then I'm good to go.
snklvl100:
Is there some ''overshoot'' or ''undershoot'' when rotating these rc servos? I mean for example rotating 90.4 degrees one time, then 89.4 another time instead of 90. I'm asking because if this is the case, after "prolonged" use the angle might be so off that the blocker won't be blocking all the beam anymore.
If the electronics inside the servo motor housing takes care of this and even if tiny overshooting /undershooting exists but they won't build up, then I'm good to go.
The whole purpose of a servo design is that it goes to a certain position every time according to a given signal.
AWOL:
Why not make it fail-safe, by weighting the shutter so that it will automatically return to the blocking position in case of power-failure?
Which would of course, not be consistent with using a servo.
The projector may however have 5V available on a USB connector, which would cover the power-failure situation.
Is there some ''overshoot'' or ''undershoot'' when rotating these rc servos? I mean for example rotating 90.4 degrees one time, then 89.4 another time instead of 90. I'm asking because if this is the case, after "prolonged" use the angle might be so off that the blocker won't be bloking all the beam anymore.
So how much $$$ you have to spend on this project? From what I've seen typical hobby servos generally can be positioned within 1 deg. If your shutter setup is where it can be bumped or come in contact with other objects.equipment, you may need a stronger setup.
Paul__B:
The whole purpose of a servo design is that it goes to a certain position every time according to a given signal.
Yeah, but how is it in reality vs expectation?
I saw some videos of jittery movement for some rc servos.
The projector may however have 5V available on a USB connector, which would cover the power-failure situation.
During a power failure the projector will shut down too, so I dont know how that helps.
What will happen during power failure? I'm thinking of having code to quickly rotate to 0 degrees when powered on, in case it was powered off unexpectedly the previous time.
If the servo has some way to know at what angle it is when powered, this shouldn't be a problem right?
snklvl100:
Yeah, but how is it in reality vs expectation?
I saw some videos of jittery movement for some rc servos.
So you saw some videos of crappy constructions.
snklvl100:
During a power failure the projector will shut down too, so I don’t know how that helps.
Precisely. If the projector is powered off, the shutter position does not matter!
snklvl100:
What will happen during power failure? I'm thinking of having code to quickly rotate to 0 degrees when powered on, in case it was powered off unexpectedly the previous time.
If the servo has some way to know at what angle it is when powered, this shouldn't be a problem right?
Assuming you intend to use an Arduino to control this (which is arguable, as a NE555 can control a servo perfectly well), the Arduino - even using the bootloader which delays it a couple of seconds - will reboot far faster than the projector lamp!
And incidentally, the servo retains its last position when powered off (unless you use AWOL's idea which I obviously do not advise). The difference between that and a stepper, is that the servo knows where it is.
