this is my first post on this forum, and I am in need of some help. I'm making a project for work. I need to make a miniature mock-up of a parking gate as part of a demo rig to show customers. I have free reign on this, so I can make it as big or as small as I want. I'm thinking something fairly small, maybe a pedestal 2' tall, and a gate arm that is 1' long.
I am in need of a couple things:
I need a servo motor that rotate back and forth 90 degrees. From my research, I'm assuming I can use 2 limit switches (one on either end). I've also considered using a motor that travels the same direction, but then using linkage to actuate the arm up and down (think similar to a train wheel linkage). The gate arm needs to travel from horizontal to vertical and back. The material used can be anything, from foam to wood to metal. What kind of motor should I use, and what is the easiest way to get the arm to do what I want? I saw a video on the "I like to Make Stuff" youtube channel where he made an arduino controlled blast gate dust collection for his workshop. (Fully Automated Dust Collection powered by Arduino // How To | I Like To Make Stuff - YouTube). I would like to do something similar, but just use the motor to raise and lower the arm 90 degrees. He says that he uses the arduino to control the amount of rotation. Is this true?
The other thing I need to figure out is how to get the motor to go on command. The controller I'm using is an I/O board, so I fire the input, and the output relay closes to send voltage to the motor to raise/lower the arm. I need to motor to stay "rotated" while the input is fired, then rotate back when the input is off. Essentially supplying power to it when the input is on, but not when it's off. From looking around on Google and other sites, the arduino seems to control that function. I do not want this. If I have to use an arduino, I can and will, but I would prefer not to.
You have not said what your project is intended to demonstrate.
If all you want is a moving model in which the arm moves up or down when you operate a switch then a hobby servo would be by far the simplest thing to use. There would be no need for any limit switches and the whole thing can be controlled with simple Arduino commands such as gateServo.write(90); to make it move to the 90° position.
It's intended to demonstrate card access. Ie, the valid card is read, which then tells an input to fire. A corresponding output relay closes, and the gate arm goes vertical. After a preset amount of time (ie, 5 secs), the input turns off, opening the relay, and the arm returns to the horizontal position.
I can utilize an output relay to talk to the arduino, correct? The output is on a proprietary input/output board, and is required.
The arduino can drive a relays which run a motor to lift or lower the gate arm.
I imagine that the gate has sensors to prevent it from coming down if the vehicle is still under the arm. This feature is described as obstruction sensing on the commercial units.
Edit: If this is a demo model, then a suitably sized hobby servo will work (as Robin2 suggested).
I would add that you will likely want to add a counterweight so that the servo is not working the whole time supporting the weight of the arm.
@vinceherman: yes, that is exactly what I mean, just on a smaller scale. The arm would be, at most, a foot long, and made out of something light, like lexan or plexiglass and painted. I'm not worried about sensors or anything like that, as it's just going to be sitting on a table top, and the arm will be moving up and down. Nothing will be "driving" up to it or anything like that. I'm just showing the ID card read will make the arm go up or down. But it (the gate/arduino) has to be tied into the proprietary board on a relay output. So the out will go from NO to closed, and the arduino will start the motor, rotate it 90 degrees, pause for 5 secs, then rotate 90 back the other direction, lowering the arm.
I'm not worried about the code part, I can figure that out, I just want to make sure the arduino has an input where that relay from the proprietary board can be tied into, and that input will "turn on" the motor, then turn it off. I also need to know if I can program the motor to go in reverse as well (to lower the arm). And if anyone has another way to raise and lower the arm, I'm open to suggestions. I have to figure out how to translate the rotational motion to linear. If someone has another way to do it, maybe just linearly, I'm open to it.
Does any one know what size motor I should get? Brand? RPM? Torque? I've no clue when it comes to hobby servos and motors. There is a hobby shop that I can go to that's close, but I need to know what to tell them when I go in.
A standard RC servo should work.Maybe get 2 in case you strip the gears learning to use a servo. (try not to turn the servo arm manually)
When you get it, run the servo sweep tutorial. If you have a potentiometer, run the knob tutorial.
I was working on the edit for this very point.