Hi, I want to drive a dc motor (pulled from a cordless hand vacuum) and be able to turn it on and off using the pololu mini maestro 18 servo controller (I already have one). I am using the pololu mini maestro 18 servo controller because there are several hobby servos I am also controlling (all part of one big project). The whole project will be connected to my laptop computer and controlled from there (USB connection).
The specs for the DC motor are as follows:
Operating Range: 9-15V
Nominal Voltage: 14.4V
No Load Current: 1.8A
Maximum Efficiency Current: 9.16A
Stall Current: 46.6A
My question is - do I need to buy the pololu motor driver or pololu motor controller to be able to do this? I guess I am supposed to connect the pololu motor driver or pololu motor controller to the channel I want to use on my pololu mini maestro 18 servo controller. Is that how it works?
Also, do I need to use a capacitor? If so, what size capacitor do I need? Do you think Radio Shack will have them?
Lastly, about power supply. I don’t want to spend too much money and I don’t know if I want to buy a professional power supply that is like many many amps because it looks scary and I would be scared if someone in my house touches it by accident and gets shocked to death. But, if you don’t think like say a 15V 50A power supply will kill people, then let me know and maybe I can reconsider. I say 50A because the stall current for the DC motor is listed as 46.6A, so I assume I have to buy a power supply that can supply at least 46.6A? I have a laptop ac adapter power supply that is 16V 7.5A - and I think I can get another laptop ac adapter power supply that is 15V 10A. Can either of these work? Can use a little underpowered power supply if I make sure to use it with a capacitor? If this is not correct, can you recommend what would be the smallest power supply I could use (and let me know if I need a capacitor or not - and what size)?
That’s a fairly high-power motor, and yes, you will need a motor controller for it. As long as it won’t be near stall for prolonged periods of time (which would probably be bad for the motor anyway), our Simple Motor Controller 18v25 should be able to handle the load. The SMC includes a power capacitor that you definitely should install as indicated in the user’s guide; you should consider adding extra capacitance if you experience power issues or have power leads longer than a few inches. The SMC can be configured to run in RC mode, which would let you control motor speed with the servo output from one of your Maestro’s channels. The SMC can also be directly controlled from a computer via USB, just like the Maestro, so you might not need to use the Maestro for motor control.
If you have a power supply capable of 50 A, you probably won’t have to worry about the effect of current surges that can occur when your motor is starting from rest or rapidly changing direction. A 10 A power supply will be underpowered for your motor, but you might be able to make it work if you use the SMC’s acceleration limiting features to minimize acceleration-related current spikes and keep the motor load low. Note that using underpowered power supplies is a good way to introduce all kinds of weird problems into the system, so we strongly discourage it. In general, PC power supplies are a cheap way to get 12V, but you have to screw around some to get it to turn on without a motherboard attached. 12-15V is not going to be dangerous–just don’t stick anything in the power supply.
Ben, thanks for the response. I have been able to successfully use a 750Watt computer power supply at 12volts for my motor. My power supply is able to provide up to 60A at 12volts, so, for now, my power issues seem to be OK.
Thanks for the recommendation about the Pololu motor controller. I would be interested in buying a Pololu motor controller, but I would really like an already assembled controller. It is not convenient for me to solder anything where I currently live. Thus, do you think I could use the Pololu Simple High-Power Motor Controller 18v15 (Fully Assembled) instead?
According to the specs I listed above, the motor should be running at 9.16A most of the time (am I reading that right?). I only expect it to go up to 46.6A (stall current) when the motor starts up each time - and that should not be very long each time. I don’t predict any kind of load during normal operation that would cause the motor to stall - or to go anywhere near stalling.
So, with that in mind, do you think that the 18v15 (Fully Assembled) would be acceptable? Thanks.
9.16 A is just the current at which your motor will be the most efficient; how much current your motor actually draws will depend on your load. The SMC 18v15 controller should work for you if you really are able to keep the continuous current at a level that the controller can handle (i.e. below 15 A) and limit the magnitude of your current spikes (e.g. by using the controller’s built-in acceleration-limiting feature). These are pretty big “ifs”, though, so I really can’t guarantee that it will work for you, and for a motor that size, our highest power controller would be more appropriate. If I may ask, why is soldering impractical for you?
You should also note that the terminal blocks on the assembled SMC 18v15 are only rated for 15 A, so I can’t guarantee they will tolerate your motor’s start-up current well. It’s not like they will melt the instant you try to draw more than 15 A, but I want to make sure you’re aware that your application will probably be periodically using them out of spec.
