AX2850: 0.2 second response delay!?

13 years 5 months ago #18302117 by sbrennan
AX2850: 0.2 second response delay!? was created by sbrennan
Please help us with a show-stopper problem!<BR><BR>We recently purchased three of the AX2850 speed controllers, and we are observing some very significant delays in the speed controller response. These are so large that they are destabalizing our control loop for our robot. <BR><BR>We just finished testing the closed-loop latency for the 2850 in BOTH analog and RS232 modes, and in the analog mode, we confirmed that our speed command had less than 0.01 sec delay going to the speed controller, e.g. we read our own analog output command using an analog input and observed only 0.01 seconds latency.<BR><BR>But we are seeing roughly 200 to 250 msec delay in motor response!<BR><BR>We've played with deadband settings, etc. but to no avail. Is there any possible way to eliminate or at least reduce this loop delay?!<BR><BR><BR><BR><BR><BR>

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13 years 5 months ago #18302691 by cosma
Replied by cosma on topic Re:AX2850: 0.2 second response delay!?
The loop delay should be 16 ms.

However, every command change will be limited by the acceleration parameter.

Make sure you set the acceleration to minimum. Is the controller operating in closed loop or open loop?

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13 years 5 months ago #18314025 by sbrennan
Replied by sbrennan on topic Re:AX2850: 0.2 second response delay!?
It is operating in open loop (we are closing the loop using an external real-time system).

We thought acceleration should be set to maximum (for maximum responsiveness). We'll try minimum and see if that helps. Will repost with results later today...

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13 years 2 months ago #20570131 by gary
Replied by gary on topic Re:AX2850: 0.2 second response delay!?
Is the loop delay in the specs somewhere? I've been looking for it without success. Is it the same for all the controllers?<BR><BR>And why do you set the acceleration to minimum?<BR><BR><BR>

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12 years 10 months ago #23220565 by scrubscrout
Replied by scrubscrout on topic Re:AX2850: 0.2 second response delay!?
Using a real-time PC-104 computer with a sample time of 1 millisecond and an optical encoder I measured the delay to be over 1 second!!

I tested the the delay in the serial command and in the response of the optical encoder and both are negligible--on the order of milliseconds.

Why does the motor controller take over 1 second to respond? Can it be sped up?

I've tried using the maximum and minimum acceleration, also with and without the watchdog and nothing helps. Changing the acceleration only changes time to reach the commanded velocity (as expected) but does not change the delay time between the serial command and the actual response of the motors.

I also tested to see if part of the delay was due to the play in my drive chain, however, when accelerating from a forward velocity to a greater forward velocity was only 10 milliseconds less than accelerating from a reverse velocity to a forward velocity. Thus the slack in my chain is only about 10 milliseconds of the 1 second delay.

How is this improved???

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