hzhang
Registered: 10/08/08
Posts: 6
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Reply with quote | #1 |
We are trying to limit the motor power (current) to keep our robot safe...
We have linked the AX3500 controller to the Roborun software, and set the Amps limit to 8, (the lowest possible setting). After puting load on the motor, the current can go up to 18A, shown from the run status tab. Is this a known issue? Any fix or workaround for it?
Thanks.
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cosma
Moderator
Registered: 04/10/04
Posts: 533
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Reply with quote | #2 |
There was an issue with amps reporting on Roborun version prior 1.9d. It may be that this is what is causing what you observe.
Try installing the latest revision of Roborun and firmware http://www.roboteq.com/doclink.html
Also, try setting different values of amps limits.
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hzhang
Registered: 10/08/08
Posts: 6
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Reply with quote | #3 |
Yes, we are using the latest firmware / roborun. But the current limit seems make no effect. |
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cosma
Moderator
Registered: 04/10/04
Posts: 533
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cosma
Moderator
Registered: 04/10/04
Posts: 533
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Reply with quote | #5 |
We cannot replicate your problem.
Make sure that after setting the new amp limit you save it to the controller.
Insert an amp meter between the battery ground and the controller and measure verify that the current measured by the amp meter is around the same as the one reported by roborun (within 10%)
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hzhang
Registered: 10/08/08
Posts: 6
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Reply with quote | #6 |
We have tried to use a multimeter to measure the current going to the motors. We have compared actual current reading from multimeter v.s. the reading from roborun software in two cases -- 1) Amp limit set to 8A, Volt limit: None. The actual current readings matched the roborun reading. But, it can go well above set amp limit. 2) Amp limit set to 8A, Volt limit: 50%. The actual current readings were 2 times of the roborun reading. And, the current still goes beyond set amp limit.
Does this mean the controller board is defective?
Thanks for your attention!
- Haiyang
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cosma
Moderator
Registered: 04/10/04
Posts: 533
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Reply with quote | #7 |
The controller measures the current going from the battery.
The current going through the motor can be higher. Theoretically, the I Motor = I Bat / Power Level. So at 50% you would see twice as much current in the motor than what comes out of the battery.
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hzhang
Registered: 10/08/08
Posts: 6
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Reply with quote | #8 |
Ok.
But, our question is really about the "Amp limit" doesn't work -- The current goes beyond the set limit (8A), no matter you look at from the battery or motor side.
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tonysantoni
Registered: 04/16/04
Posts: 28
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Reply with quote | #9 |
Hello
This is Tony Santoni, with Roboteq.
I have just tested a AX3500 with amp limit set to 8 Amp.
I have connected a 12 Volt power supply and two 1 ohm resistors, one per channel,
The controller limits the current at 8 Amp PER CHANNEL, total being 16 Amp.
Are you by chance working in same conditions, that is two loads ?
Current limiting is per channel, not per controller.
Otherwise if you can describe your setup, I will try to replicate and see if I can duplicate your findings.
You can also reach me at tony@roboteq.com
Tks
Tony
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Robotony |
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hzhang
Registered: 10/08/08
Posts: 6
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Reply with quote | #10 |
Hi Tony,
Our setting is similar to yours. We have 24V battery set, two motors connected -- one motor on each channel. The current limit is set to 8A. The multimeter is connected to one motor.
I run this motor from the roborun software panel. The current reading from roborun matches that of the multimeter, but both current readings exceed 8A a lot.
Thanks for your help.
- Haiyang
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tonysantoni
Registered: 04/16/04
Posts: 28
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Reply with quote | #11 |
You should measure the battery current, not the motor current.
Can you pls do this putting the current meter on the battry wire and tell me what do you read ?
Also pls tell me the series resistance of the motor.
with these datas I can probably make sense of what you see.
Tks
tony
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tonysantoni
Registered: 04/16/04
Posts: 28
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Reply with quote | #12 |
I forgot; also the series inductance of the motor would help.
normally it is published in the motor data sheet.
tks
tony
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hzhang
Registered: 10/08/08
Posts: 6
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Reply with quote | #13 |
Hi, we measured again on the battery side, with one motor plugged into controller. Current limit set to 8A. But the current can goes to 14-16A when the motor is loaded.
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