I need a programmable servo controller which would be able to rotate a small piece of sheet foam 45’ degrees (uncovering a hole) and then a minute later return to the original position (covering up the hole again). I don’t want to have to keep the thing hooked up to a PC in real-time to guide it.
I’m making a drying chamber for sausages out of an old freezer. When I kick on the power to the controller (timed to go on & off 2X/day) I need the program to uncover the vent doors (two of them - two servos), while a couple of vent fans (hooked up in parallel series to the timed power supply) also kick in and blow out the chamber.
So, the controller needs a) a programmable chip b) two motor drivers & c) I’m guessing some sort of PC interface like USB so I can code the chip.
Am I far off on these assumptions? I can usually muddle through any project with minimal guidance.
thanks in advance
I think our Micro Maestro USB servo controller will be able to do everything you want. It doesn’t have any integrated motor drivers, but it generates signals to control standard RC servos that have drivers built-in. You can control your fans by having them receive power directly from your timed power supply, or you could use a MOSFET controlled by a digital output from the Micro Maestro to deliver power to the fan motors on command. If you use this latter approach, you wouldn’t even need a timed power supply; you could just power everything with a battery and have the Micro Maestro do all the timing. Assuming your fans only need to spin in one direction, you don’t need the more complicated H-bridge circuitry found in bi-directional motor drivers.
You ROCK Ben!
I’m sure it will all make sense once it is laid out on my bench. The pieces of sheet foam I need to move around weight about 40 grams. I was going to use CPU cooling fans to move the air around. Using all your site’s gear, Could you recommend: which a) Maestro you would use? b) power pack - [transformer] c) software suite c) and servos.
I like the idea of pulling the fans’ power through a MOSFET. I see that Polou sells a lot of boards with MOSFETs capable of handling all kinds of power (although I was only going to pull CPU fan wattage) Which board would you use for this app since I can hard wire everything together?
Fans will be unidirectional
Many thanks again,
I suggest you use a Micro Maestro powered by a 5V 3A wall wart. You can download the free Maestro Control Center software utility from the Micro Maestro product page (see the resources tab), which will let you configure, test, and program the Maestro. We offer a lot of different servos, and the best one for your application will depend on desired speed and required torque along with how much space you have available. It sounds like speed and space might not be an issue, in which case you could go with a pair of basic standard servos.
You might also want a DC power adapter barrel jack so you have something to plug your wall adapter into, and some M-F servo extension cables could come in handy depending on how far apart your servos need to be. If they need to be a great distance apart, I suggest you just use two Micro Maestros (one for each servo).
You should look for a fan that uses a brushed DC motor as those are the easiest to control, or you could buy such a motor separately and put a fan blade on it. You will need additional control electronics if you use a fan with a brushless motor.
All you need to control power to your motors is a discrete MOSFET and flyback diode. Our RC switches would be overkill, but they’ll work if you want a simple solution. If your fans pull less than 3A combined, you could use our RC switch with small MOSFET to turn the fans on and off in response to a servo pulse output from the Micro Maestro. The RC switch has the necessary flyback diode built-in. If your fans draw more than 3A combined, you will need a different power source, or you should look for lower-power fans.
Just about the drop the hammer here. Awesome.
If I use two Micro Maestros ( distance between the servos will be about 8’ - 245 cm) how do I get them to sync up, because the fans need to go on/off in unison…or nearly so. A lag of a few seconds will not matter.
Any problem to split the power supply over this run? I’m used to working with line voltage.
A fan that will blow out the chamber in a minute will only pull 1/3 amp so both should not draw more than 0.75 amp.
It seems that pretty much all PC & small electronic cooling fans are brushless. It might be easier to add a circuit to the controllers than build two fans & housings. What circuitry would I need to put to run brushless?
Thanks again & I’ll send you a video when I get this set up.
You can use a single power supply to power both Maestros, but it might be easier to buy a separate wall adapter for each drying chamber (especially if you already have outlets near each one). You could synchronize the maestros by making one slave to another using a signal wire to connect a channel on one to a channel on the other. The master unit would do the timing and could toggle its slave signal line when it’s time to open the chamber. The slave would be running a program that just waits for the slave signal line to go high, at which point it starts running the same servo sequence as the master. In this scenario you would also need to run a ground wire between the two Maestros to give them a common ground.
I don’t know a lot about PC fans, so I can’t help you all that much. I think most of them are brushless, but they typically have controllers built-in so that they will run off of a DC voltage. You could use fans with built-in controllers the way I was describing using a DC motor in my previous post, and you might even be able to do something simpler by skipping the MOSFET and using one of the speed control lines to turn the fan on and off (i.e. connect the fan permanently to power and have the Maestro output a digital high to turn on the fan and low to turn off the fan). I suggest you search around for projects that involve controlling computer fans to see if you can get a feel for what it would entail and whether that’s something you can easily integrate into your system. You might just want to get a cheap $10 fan and try playing around with it. We do not sell brushless motors or brushless motor controllers.
One other issue you might run into is that it seems computer fans typically run off of 12VDC, while servo power must typically be between 4.5 and 6VDC. This means you have several options:
- You can find a fan that is designed to operate at 5VDC or get a 12VDC fan that will at least run acceptably at 5VDC.
- You can use two power supplies, 12V for the motors and Maestro board power and 5V for the Maestro servo power. We sell a 12V 3A wall wart as well.
- You can use a single 12V power supply for the motors and Maestro board power and a step-down switching voltage regulator to get a servo power voltage that is in the acceptable range. We should have such a regulator available in the next few days.
All I can give you are suggestions for things that might work for you. You’re ultimately going to need to figure out what is easiest, try it, and see if it works. Don’t be surprised if the first thing you try reveals a better way and leads to a second revision with slightly different parts!
Its a single chamber w/ one fan to blow in fresh air a 2nd fan to blow the old air out.
So, if I’m running two DC-5V brushless motors with controllers built-in, (so that I do not need to worry about rotor position or Hall sensors…just add DC power… and leave the power hot…I can turn them on & of via the two maestros and power it from the same source as the servo controllers?.
So, project parts list:
Two maestros, (one slave, one master), controller software, two fans (DC-5V brushless), one common ground & one control wire, A to mini-B USB cable and two power sources (for simplicity) correct?
I’ve made inquiries about the (just add power) DC-5V brushless fans. I think they are available on Ebay for a few dollars each.
That list looks correct, although you forgot the two servos you need to open and close the chamber. Hopefully the fans you get will have a third wire for controlling the speed. Otherwise, you will need to use the Maestros to turn on and off MOSFETS that control power to the fans. You might still consider getting some servo extension cables so you have more flexility in where you place things.
Ben, good idea about the servo cables.
I’m not sure about the 3 wired fans. The two wired ones can run flat out I don’t need to control their speed, only their running time. I think with the 3 wired ones we get into having to monitor the Hall sensor.
If I’m using single wall wart (just running power over to the 2nd fan) do I need a MOSFET on each maestro, or only one on the Master?
You can get by with one MOSFET controlled by a single Maestro (the MOSFET input would come from one wall wart and the output would go to both fans), or you could use two MOSFETs (one for each fan). It all depends on which is easier for you to lay out in your system.
I’m pretty sure you can find some three-wire brushless fans with controllers built in that let you turn them on and off with a signal wire and supply DC power via the other two wires.