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| Actuator Project ( Was MRotate4) |
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| DaOld Man:
Here is a diagram of the relay and transistor I used for this project: |
| Le Chuck:
Your documentation is awesome as usual. Keep it up! |
| DaOld Man:
Thanks LeChuck, I hope it is useful. Here is the schematic diagram of my simple drive. (Any suggestions for a name for this drive? (be nice!)). I found that it is not necessary to use both contacts on the limit switches. I just wired both the terminals on the strip for each switch to just the NC contact of the switch. So I adjusted this drawing to show that, no need to use extra terminals if you dont need them. Edit: I left out one very important thing on this drawing, and that is a fuse on the power from the power supply. The fuse can be an auto type fuse, and it should be rated in amps high enough to not blow during normal operation, but low enough to blow if the motor hangs up. With the actuator Im using, I found that while the motor is running it draws around a half amp, and when it stalls it draws right at 5 amps. Why would it stall? If something happened to a limit switch and the circuit wasnt turned off when it should be, the actuator would travel until it hit a mechanical stop. This is when the motor would stall, or cant turn. Current jumps high during this time and if power isnt removed pretty quick, the motor will get hot, possible damaging the motor or the power supply. So this is where the fuse comes into play. The fuse blows (or opens up), turning off power to the circuit and the motor. I feel this is very important. Im thinking about trying a 1.5 amp fuse on this circuit. If it blows too soon, I will up the amps by .5. (The fuse must be large enough to handle the startup current of the motor, which can be much higher than the running current for a split second). The power supply must also be rated to supply enough current to blow the fuse, should the motor stall. Say for instance I use a power supply rated for 1 amp, it would probably be enough to run the motor normally, but If I use a 2 amp fuse and the motor stalls, the power supply may not be able to pump 2 amps into the circuit long enough for the fuse to blow quickly. This could damage the power supply. A good test would be to move the limit switch out of the way and let the motor stall while supervising it. Fuse should blow before anything heats up. And by supervising, I mean hand on the power cord, ready to pull the power. |
| DaOld Man:
Ok, so maybe you dont want to use relays, cause let's face it relays are old school, and they are mechanical, which means eventually they will wear out and fail, even though it may be many many years down the road, there is a point which they will give up the ghost. But in defense of relays, they are much simpler and much more forgivable about current surges and short circuits than solid state devices are. One big disadvantage for some folks would be that you cannot control the speed of the motor by pulsing the relays on and off, like you can with a solid state device. (Such as a transistor). So you are planning on using a solid state drive AKA as "H Drive", but you like the idea of using the comport to control it? Well here is a circuit that basically cuts out the relays and two of the diodes of the previous circuit, but adds two resistors, to offer an interface between the comport and the H Drive. I plan to offer PWM speed control in MRotate4 as an option. (Cant use it on the relay drive though). I havent tested this circuit, but I am pretty sure it will work, but as with all of the circuits and software I offer, use at your own risk. Connecting anything to your computer can be a risky thing. You can fry your computer if not wired properly. I have tested the relay drive on my main desktop PC with no problems at all, but keep in mind you are doing this at your own risk. |
| DaOld Man:
This might be a better circuit for the H drive. Notice that in this circuit, when a limit switch opens, the input on the H drive will turn off immediately, and not rely on the software turning it off. Let me add also the same speech I made above about the fuse. |
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