Author Topic: Accuracy of Spartan 6 FPGA PWM  (Read 15340 times)

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Offline Rufus

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Re: Accuracy of Spartan 6 FPGA PWM
« Reply #25 on: March 05, 2013, 11:33:28 pm »
Taking advantage of true FOC with stepper motor one could achieve something like this:

If you are going to have the complexity of a full positional feedback servo loop why would you choose a stepper motor?

 

Offline Hypernova

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Re: Accuracy of Spartan 6 FPGA PWM
« Reply #26 on: March 06, 2013, 08:40:18 am »
Taking advantage of true FOC with stepper motor one could achieve something like this:

If you are going to have the complexity of a full positional feedback servo loop why would you choose a stepper motor?



^This, the whole point of steppers is so that you don't need encoders.
 

Offline nctnico

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Re: Accuracy of Spartan 6 FPGA PWM
« Reply #27 on: March 06, 2013, 04:32:11 pm »
Actually you do need encoders. At least at the end and the beginning of a track or something similar. The problem with a stepper motor is that it is very tempting to skip the encoder but in the end you'll pay the price. An advantage is that you can use an encoder with lesser resolution but you can still detect you missed a step. Depending on the application it may be too late though.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Hypernova

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Re: Accuracy of Spartan 6 FPGA PWM
« Reply #28 on: March 06, 2013, 04:52:19 pm »
Actually you do need encoders. At least at the end and the beginning of a track or something similar. The problem with a stepper motor is that it is very tempting to skip the encoder but in the end you'll pay the price. An advantage is that you can use an encoder with lesser resolution but you can still detect you missed a step. Depending on the application it may be too late though.

That's the job of indexing and limit switches, the point is with steppers you get commutation and incremental positioning for next to nothing which the the usual reason people go for them.
 

Offline ciikucliTopic starter

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Re: Accuracy of Spartan 6 FPGA PWM
« Reply #29 on: March 06, 2013, 07:01:01 pm »
I'm going with stepper motors because they are cheap with pretty good rotations and have a good torque. Virtually all hobbyist 3d printers use these for this reason. If I go with foc, I'll need them for control, otherwise I'll use them to ensure that the micro steps are being completed accurately. It's a combo 3d printer/light CNC machine/ multitool, so there may or may not be resistance to motion.
 

Offline nctnico

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Re: Accuracy of Spartan 6 FPGA PWM
« Reply #30 on: March 06, 2013, 10:15:42 pm »
Actually you do need encoders. At least at the end and the beginning of a track or something similar. The problem with a stepper motor is that it is very tempting to skip the encoder but in the end you'll pay the price. An advantage is that you can use an encoder with lesser resolution but you can still detect you missed a step. Depending on the application it may be too late though.

That's the job of indexing and limit switches, the point is with steppers you get commutation and incremental positioning for next to nothing which the the usual reason people go for them.
That is true but if the load varies or can get stuck (like in a CNC machine) then you might be looking at missing steps. In such a system a stepper is not the best choice.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Hypernova

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Re: Accuracy of Spartan 6 FPGA PWM
« Reply #31 on: March 07, 2013, 01:06:33 am »
Actually you do need encoders. At least at the end and the beginning of a track or something similar. The problem with a stepper motor is that it is very tempting to skip the encoder but in the end you'll pay the price. An advantage is that you can use an encoder with lesser resolution but you can still detect you missed a step. Depending on the application it may be too late though.

That's the job of indexing and limit switches, the point is with steppers you get commutation and incremental positioning for next to nothing which the the usual reason people go for them.
That is true but if the load varies or can get stuck (like in a CNC machine) then you might be looking at missing steps. In such a system a stepper is not the best choice.

IMO if you use budget tools expect budget results, besides by the time you use encoders there's really little advantage for steppers, you even get less wiring with PMSM (3 wires only), and with free FOC software libraries on the net it's not that hard to write code for.
 


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