Smoke released from 2x15 roboclaw.

General discussion of using Roboclaw motor controllers
ChrisA
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Joined: Mon May 22, 2017 4:32 pm

Smoke released from 2x15 roboclaw.

Postby ChrisA » Mon Jun 11, 2018 5:36 pm

I'm wondering what I could have done to have caused this...

I think I can repair (or does warranty cover this?) it but I don't want to reconnect this until I understand the root cause of the problem.

I have a 2x15 Roboclaw. I got it running with the ROS node driver and a keyboard teleoperation node. The mobile platform was on a stand so the wheels where off the ground. This was a first test of the system (after first ruling with the windows based "studio" app to tune the PID parameters.

I powered the Roboclaw with a small 7.4 volt LiPo battery. The Robot is connected via USB to a Raspberry Pi3 and I command the wheels to turn forward and then backwards three or four times then I see smoke from under the Roboclaw heat sink and the 20A fuse on the battery blows.

This Roboclaw was just returned to me from the factory, the first one had a problem and did not work out of the box, this one worked for only a few minutes

I removed the heat sink and looked. Some plastic is missing from the base of two of the four electrolytic caps. The smoke might have been from the plastic melting. There is also a small bit of brown residue on the metal heat sink, maybe from the smoke.

The question is what if anything could I be doing wrong. I chose a 20A fuse as the smallest one that could work. Same reasoning for the battery

IMG_0007.jpg
IMG_0007.jpg (179.77 KiB) Viewed 344 times

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Basicmicro Support
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Re: Smoke released from 2x15 roboclaw.

Postby Basicmicro Support » Wed Jun 13, 2018 9:48 am

The mosfets were damaged again. The plastic melting on the caps probably happened when the mosfets were replaced originally(a rework station heat gun is used to remove/replace mosfets which can cause the plastic label on the caps to shrink melt some when replacing mosfets). The fact the plastic was melted indicates the original fix was to replace the mosfets. Since they were damaged again that would indicate the cause of the failure is external to the Roboclaw(eg the motor you used, the wiriing etc..). I doubt it is voltage related since you used a 7.4v lipo).

Based on the picture the caps had no connection to the failure. Please provide more information on what you are driving and how you have it wired. The mosfets on the 2x15 are rated to 85amps and dont just fail randomly so my guess is something you are doing(trying to drive an oversized motor would be my first guess) is causing the mosfets to fail faster than the over current/temperature detection can catch it so please be as specific with your setup as possible so we can determine the cause and prevent a repeat of this failure again.

Note on fuses:
1. A fuse does not blow at its rated current. It usually blows at a much higher current than that.
2. The current at the fuse/battery is not usually the current at the motor. The motor ussually sees much higher currents(eg a motor at 50% duty pulling 20amps is only pulling 10amps from the battery(10*100% = 20*50%).

Please send it back in along with the requested information so we can repair the board and help you to prevent this from happening again.

ChrisA
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Joined: Mon May 22, 2017 4:32 pm

Re: Smoke released from 2x15 roboclaw.

Postby ChrisA » Wed Jun 13, 2018 10:51 pm

Let's figure out what is happening BEFORE I send it back.

Perhaps I need to buy a much larger RoboClaw controller. Which do you recommend? This is the load I'm driving:
https://www.pololu.com/product/1563 It is a 6 wheel drive chassis. The unit was modified to add a pair of quadrature encoders to the center pair of wheels. These encoders are wired to the RoboClaw.

Power comes from a 7.4 volt LiPo battery (which could be charged up to 8.4 volts. The battery leads are fused at 20A with an ER301 rectifier diode (with 125A surge rating) wired "backwards" across the fuse.

There are six motors in two sets of three. Each set is wired in parallel. In typical use I see about 1 amp per side.

Because the RoboClaw stopped working I am now using the driver linked below paired with an Arduino Uno and the same 7.2 volt LiPo battery
https://www.ebay.com/itm/1pcs-Dual-VNH2SP30-Stepper-Motor-Driver-Module-Monster-Moto-Shield-Replace-L298N/141976891751
I'm using a simple PID loop. The VNH2SP30 chip seems to be able to drive the 6 wheel chassis without getting warm. The VNH2SP30 data sheet claims hardware current limiting that is safe for a short circuit although I've not tested it.

So THAT is my use case. The Pololu web page is very detailed.

The RoboClaw failed (with some smoke) when on a test stand with the wheels about the ground. It might have been during a forward to reverse direction. It was being controlled via the USB cable from a Raspberry Pi running the ROS Node software from your web site.

I figured the I could set the current limit on the RoboClaw and it would be a hard limit so I keep it at 6 amps per channel.

Let me know what you think. If this is the wrong application I will use the 2x15 RoboClaw for something else.

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Basicmicro Support
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Re: Smoke released from 2x15 roboclaw.

Postby Basicmicro Support » Thu Jun 14, 2018 8:59 am

Yes, we prefer to determine what caused a failure before a controller is sent back as well but that isn't always possible.

I've driven a similar 6 wheel robot with a 2x15 with no problems. In fact the motors we used on our 6 wheel where more powerful than the dagu and ran at a higher voltage. Your failure happened when it wasnt under load as well.

Based on that I don't see why it failed either time. My suspition is some other component in the control loop id faulty and wasnt caught when we ran our tests on the repaired controller. I suggest we swap the controller out entirely.

Send the controller back and email support@basicmicro.com and we will ship you a replacement.

When you get the new one I recommend you test the robot with the 2x15 without the encoders connected first using ion studio. Then test with encoders using ion studio. And then finally with ros.

ChrisA
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Joined: Mon May 22, 2017 4:32 pm

Re: Smoke released from 2x15 roboclaw.

Postby ChrisA » Thu Jun 14, 2018 12:47 pm

Tanks for you help.

Yes I always test in that order, run motors open loop to verify basic operation and the direction s correct. Tun PID parameters in "Studio" then very simple tests using ROS. I was dong that last step when the failure occurred.

I was worried the 2x15 might be under sized what I re-read that motor stall current is about 7 amps. If all three wheels stalled the current would be 21 amps, More then the 15A rating of the controller. So 15 is a maximum continuous current not maximum peak?

The test that cause the smoke was running forward then reverse using ROS_Node and ROS teleoperation on a test stand. Possibly the forward to reverse transition caused a stall current on all wheels.

One more possible factor. I found I was using a "DC extension cable" I use it so the battery can be remotely located. For indoor testing I keep battery in a fireproof container. This extension cable had a fuse with no diode. I bet THIS was the fuse that blew All fuses were 20A. The on-robot fuse has the diode paralleled to it.

Let's say the direction reverse pulled 7 x 6 = 42 amps from the battery, fuse blew and could the motors de-energizing have created and over voltage? Yes I know placing fuses in series is pointless but I had a fire a couple years ago with high current DC -- prototype robots can sometimes eat cables causing short

I need to scrub the heat sink grease off the MOSFETs, read the part numbers and get a data sheet.

Thanks again, I will send the unit back after I hear from support@basicmicro.com

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Basicmicro Support
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Re: Smoke released from 2x15 roboclaw.

Postby Basicmicro Support » Mon Jun 18, 2018 5:04 pm

Correct. We rate the 2x15 to 30amps per channel peak and 15amps continuous. Temperature of the board dictates the allowed maximum current. Even if you were running motors totaling more than 30 amps at stall it should not have smoked. We test all the controllers on motors much higher than rated to make sure they wont fail like that. With the latest firmware we've tested even our 2x7A controllers running a 500+ amp stall motor. It doesnt run it well but it survives it just fine.

About the only thing that can kill our boards now(besides some random bad part not caught by testing) would be a dead short on the motor channels.


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