How to tell when the stepper motor is done stepping

arduinostepper motor

I am working on a project that requires mildly accurate positioning of the x and y axis. It involves an airsoft gun and it is basically a motion tracking turret. Because of the requirements for movement that could be tracked I determined that a stepper motor would probably be the best option. I have ran into a problem though while picking the motor and a driver or even if I am going to stay with the stepper motor idea. My question is how do I know when my stepper motor is done moving like is there a pin that goes low on most drivers saying that the motor is done moving? Or should I just move onto using a servo. I choose stepper motors because they were powerful and relatively cheap but I don't really understand how to control them. I understand the whole signal sending idea and I will be using the accel-libary with an arduino to control it but how do I know when to give the motor a new position. Also as a side note will a motor with a torque rating of .1416 in-pd's I will be using a .5pd airsoft gun and will mount it in the middle of it's center.

Best Answer

Stepper motors are actually not very powerful compared to a geared DC motor, but they have the advantage of providing accurate positioning without needing a feedback mechanism. The whole idea of a stepper motor is that it only moves when you step it, otherwise it stays put. So the answer is, it's done stepping when you stop stepping it!

However this only works reliably if you:-

Don't step too fast, or accelerate and then try to slow down too quickly.
Supply enough holding current to stop it from slipping under heavy load.
Have some way to detect or set the 'home' position.

Some early disk drives set the home position by simply stepping in one direction enough times that the mechanism must have hit its end-stop, which would make a horrible clattering sound if the heads weren't on the innermost track!

Related Solutions

Electronic – Stepper Motor Control Timing

As Nick T mentioned, TCP/IP is unfiltered and non-deterministic. You said you want to also interface with SPI and UART devices, and previous versions used USB. These are difficult to do in real time, and probably require significant code space.

On the other hand, you want real-time control of your stepper motors, which requires deterministic execution and rapid interrupts but not a lot of program space.

While you said you wanted to avoid using a separate microcontroller because it would complicate things, this is a perfect example of when you need a co-processor, and I believe that it would make things simpler in the end.

You can develop simple stepper motor controller firmware that run on small, cheap microcontrollers. Design (or discover) a protocol that can use a communication bus available in hardware on whatever controller you choose. I'd recommend SPI for this (on a different channel than the device you mentioned in your question; your master should have two SPI peripherals), you don't want to mess with address conflicts given the small number of controllers you'll have. Don't do anything with this controller but run the stepper according to the data it receives over the protocol. You can probably buy something that does this already. The goal is to be able to treat this as a hardware peripheral.

Then, you can develop USB or Ethernet controllers that will plug into these devices. You will have flexibility in the host protocols (Need to use RS485 this time? No problem!), you can use different numbers of motors, and you have greater modularity for designing, testing, debugging, repairing, and replacing. The only reasons I'd try to implement something like this in a single controller would be extreme cost/size restrictions, and/or a lack of hardware modules (like PWM? Did I miss something?) that could do this without interrupting the host processor.

Electronic – how can i understand when a stepper motor get a complete round

Stepper motors usually have a sensible number of steps per revolution, 100, 200, 400 are popular numbers. So my guess would be that 1600 is the precise value for your motor.

The way to check it is simply this:

for (i=0; i<400; i++)
{
    pause_ms(100);

    for (k=0; k<1600; k++)
        take_one_step();
}

Watch what happens. If the number is exactly 1600, then you'll simply see the motor rotate 360º 400 times, with a 0.1s pause between each rotation.

If the number was actually 1599, then you'd see the motor pausing at a slightly different place each time. And after 400 revolutions, would end up facing 90º from where it started.

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