Very little output power

11 years 5 months ago #29524962 by jrrice
Very little output power was created by jrrice
I\'m using an Ax1500 with two brushed 24 volt motors. One motor in open loop speed control and the second in closed loop position control with a 1k feedback pot. Running in RS232 Mode on either motor I get extremely little current draw. Just running motor 1 in speed mode with a 24 volt battery supply, current limit set for maximum current, and speed command set to maximum, the motor runs as expected with the change of speed command. Except that the measured maximum current I see using a amp meter at the battery is 140mA. The current is so small that it won\'t even register on the roborun plot, and the maximum recorded power on the plot is 39. Looking at the PWM signal at the motor with an Oscilloscope, I am only getting a 0% - 30% duty cycle change for an input command range of -127:127.

With the second motor running in position feed back at the same time, I can get a maximum current draw of 670mA from the battery. The power on the second motor is to small to even turn the motor through its gearbox.

Any help would be appreciated, thanks.

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11 years 5 months ago #29524963 by cosma
Replied by cosma on topic Re:Very little output power
Low current shouldnt be a problem by itself. If you have no load on the motor and the motor, is efficient, it is normal that you would see very little current even at full speed. It is when you try to load it that you would see the current increase.

The AX1500 amps reading resolution is 250mA increments. So 150mA may not be readable.

The 30% PWM is more abnormal. Run the motors in open loop. Verify that the Power box in the Roborun Run tab equals the command value you put in with the slider.

If you are using v1.9d or 1.9e of the firmware, make sure you did not limit the power output in the Power tab.

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11 years 5 months ago #29524964 by jrrice
Replied by jrrice on topic Re:Very little output power
I aggree that low output power in itself is not a bad thing especially under a no load situation. But, for my first motor which is being run in open loop speed control mode, its maximum rpm is much lowwer than I would expect. For the second motor running in position control mode, its not getting enough power to turn. The other thing I have noticed is that when adjusting the PID gains for the second motor, if I turn Diff and Integral gains to zero while turning Proportional gain to its maximum, I get a power output of about 8 on my plots. If I adjust Integral gain to any amount, it will ramp up to a power output of 39. Now I understand why the output power ramps up when the integral gain is introduced because the motor is never moving into position, but why does it stop at 39. What does 39 mean as far as power goes? 39 Watts? 39% duty Cycle? Also, there is no indication of errors or of the power transistors getting hot. The temperature on the transistors never gets above 36c.

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11 years 5 months ago #29524968 by cosma
Replied by cosma on topic Re:Very little output power
39 would be 39/127th, or about 20%.

There is no reason that power should cap at 39. The integrator in the PID normally keeps increasing power as long as the error is <> 0.

Check in open loop that you can get 127 (100% PWM) power level in Roborun.

If not, report which version of the controller and the firmware you are using. Try reload the firmware so that the default configuration is loaded in the controller.

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11 years 5 months ago #29524969 by jrrice
Replied by jrrice on topic Re:Very little output power
I am running motor 1 in open loop speed control and I am getting the same result of power read is max at 39 for a command input of 127.

I am using software rev: v1.9e 01/14/09. Hardware Code: 1-3-3 1 FET per Leg Dual Channel. Controller Configuration Utility v1.9d 02/15/08. I will try to reload both software and firmware and if it helps.

In your previous response you asked me to check that I did not limit the power output in the power tab on Roborun. I am assumming you meant the current limit, and I set this in the middle of the slide to make sure that I was not confusing which setting was the minimizing setting. No matter where I move the slide, I get the same results.

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11 years 5 months ago #29524972 by cosma
Replied by cosma on topic Re:Very little output power
With 1.9e firmware (must use 1.9e roborun), you can cap the output level.

Make sure you have 1.9e roborun, and reload the firmware to start with clean default parameters.

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11 years 5 months ago #29524973 by jrrice
Replied by jrrice on topic Re:Very little output power
Using the new Roborun 1.9e fixed the problem. Thanks.

Now the issue is, for the position control loop, using roborun I cannot set the proportional gain high enough to move the motor and gearbox. Even adding in the max derivative gain, the motor will not move with out the addition of integral gain. With the integral gain set, proportional and derivative gains have little to no effect. Is there anyway to increase the P and D coefficients beyond what the slider provides? Running the motor with just an Integral controller causes it to be jerky, as you can imagine.

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11 years 5 months ago #29524975 by cosma
Replied by cosma on topic Re:Very little output power
Unfortunately, this can\'t be changed. See if you can wire your pot, or use values that would create a larger error.

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11 years 5 months ago #29524979 by jrrice
Replied by jrrice on topic Re:Very little output power
I tried setting my I and D gains to zero and using the equation given in the manual for calcuating applied power:
Applied Power = (command - actual Position) * P Gain
My calculation come out larger then what the controller is using.

Next, I tried reading the the gains from the board. On page 141 of the AX1500 Manual the address for the gain are:
^82 - P1
^83 - P2
^84 - I1
^85 - I2
^86 - D1
^87 - D2

In Section: Reading and Changing Operating Parameters at Runtime, It gives the addresses as:
^82 - P1
^83 - I1
^84 - D1
^85 - P2
^86 - I2
^87 - D2

Setting the PID parameters with Roborun, saving them to the board, recycling power, and reading the address gave me the following results:

P,I, and D all set to 1:
^82=03, ^83=03, ^84=01, ^85=01, ^86=02, ^87=02

P,I, and D all set to 0:
^82=02, ^83=02, ^84=00, ^85=00, ^86=01, ^87=01

P,I, and D all set to 63:
^82=41, ^83=41, ^84=3F, ^85=3F, ^86=40, ^87=40

With all gains set to zero, I was still able to get command outputs. I reset the board to its default settings and repeated this exercise with the same confusing results.

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11 years 5 months ago #29524981 by cosma
Replied by cosma on topic Re:Very little output power
We\'ll investigate but keep in mind that the PID parameter that you change with the ^82... commands, change the values in RAM. These do not get saved in Flash.

At power up, the values that are in the Flash configuration are copied in these RAM location.

The correct order is P1,P2,I1,I2,D1,D2

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