Re: Motor shield

Measuring between two terminals of M1, M2, M3 and M4, the voltage is zero. When I measure either one of the terminals of M1 W.R.T. GND, the voltage swings between +12V and -12V. The same results are true for M2, but not for M3 and M4. There is no voltage measured at all for M3 and M4 using any measurement points.
wzchang

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Joined: Sun Feb 24, 2013 7:16 pm

Re: Motor shield

Corrections The voltage swings between +12V and 0, when measured between the GND and either one of the terminals of M1 or M2.
wzchang

Posts: 18
Joined: Sun Feb 24, 2013 7:16 pm

Re: Motor shield

Corrections The voltage swings between +12V and 0

Good. Because a negative swich WRT GND is impossible. The H-bridge can only switch between 0 and +12v. They way it reverses the motor is to switch which pin it is sending the 12v to.
Measuring between two terminals of M1, M2, M3 and M4, the voltage is zero

That is not a good sign.
When I measure either one of the terminals of M1 W.R.T. GND, the voltage swings between +12V and -12V.

That is curious. If the voltages on the terminals are ramping up and down, but the voltage between the two terminals is 0, then the two terminals must be ramping up and down together. But based on the code, they should be 180 degrees out of phase. I can understand how half of an H-bridge might be damaged and not respond. I'm not sure I understand how it would do what these measurements indicate.
There is no voltage measured at all for M3 and M4 using any measurement points.

I guess we can assume that the second L293D chip is dead.

I believe you mentioned that you had two of these boards. How does the other one perform?

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Re: Motor shield

I have the 2nd set of motor shield but not assembled.
wzchang

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Joined: Sun Feb 24, 2013 7:16 pm

Re: Motor shield

OK then. Lets first swap the L293D chips on the board. Exchange the M1/M2 chip with the M3/M4 chip. Then run that sketch again and see if the measured voltage behavior follows the chips.

If it does, then there is most likely some damage to the chips. If not, then the problem is in the assembly of the board.

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Re: Motor shield

I just swapped the chip, and the results of M1 and M2 measurements are identical yesterday's. M3 and M4 are not quite the same, for a couple of times the voltage swings between one of the terminal and the GND, but not consistent.
wzchang

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Joined: Sun Feb 24, 2013 7:16 pm

Re: Motor shield

Then it is likely that we are dealing with some assembly issues. Is it possible to get some closer photos of the board so I can examine the components and solder joints in detail?

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Re: Motor shield

I just attached several closeup shots, hopefully they are complete, and useful. Please let me know which part of the board you would like me to retake them. Thanks.
Attachments
closeup_solder22.JPG (96.52 KiB) Viewed 453 times
closeup_solder.JPG (175.04 KiB) Viewed 453 times
wzchang

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Joined: Sun Feb 24, 2013 7:16 pm

Re: Motor shield

Some are a bit out of focus. I circled the ones that look most suspect, but I recommend going over the whole board and re-touching any that are not smooth and shiny, or have not flowed well onto both the pin and the surrounding solder pad. The ideal joint should have a cross-section like the diagram below. Our soldering guide has some tips on fixing common soldering problems: http://learn.adafruit.com/adafruit-guid ... n-problems

Attachments
closeup_solder22.JPG (166.9 KiB) Viewed 443 times
closeup_solder.JPG (328.55 KiB) Viewed 443 times

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Re: Motor shield

Hi
I did touch up the solder spots, and ran the code you sent me. The only difference I observed from the last time was that the voltage I measured between Gnd and one of Motor's terminal had the same behavior, namely, the voltage swung between 0 and 12 V for all M1-Gnd, M2-Gnd, M3-Gnd and M4-Gnd. The last time I saw the inconsistency in M3-Gnd and M4-Gnd. Still, there is no voltage can be measured between terminals and this is also consistent among all four Motor terminals.

In addition, I replaced two L293 chips with my brand new chips from the other package just opened, and the same behavior is observed. Then I switched them back to the original chips.

Is there anyway you can help me to figure out why there is no terminal voltage measured for all Motor terminals? Thank you very much!
wzchang

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Joined: Sun Feb 24, 2013 7:16 pm

Re: Motor shield

So there was some change there. Let's get some more photos. Both the back and the front of the board this time.

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Joined: Sat Feb 07, 2009 9:11 am

Re: Motor shield

Thank you for your support on Sunday! Please see attached photos with one of front and two of back.
Attachments
back_img2.JPG (146.94 KiB) Viewed 398 times
back_img1.JPG (132.08 KiB) Viewed 398 times
front_img.JPG (130.61 KiB) Viewed 398 times
wzchang

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Joined: Sun Feb 24, 2013 7:16 pm

Re: Motor shield

There are still a few solders that look suspicious to me. They don't seem to have flowed onto the pads:
suspicious_solders.png (412.25 KiB) Viewed 393 times

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Location: Buffalo, NY

Re: Motor shield

That's a big improvement on the bottom side. Still a couple spots that need work as Driverblock pointed out. The top-side needs some work too. In particular the digital I/O pins 8-13.

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Re: Motor shield

I re-soldered the points you pointed out and please see attached. Then I made the run using the same script, and the results were the same as the ones obtained the day before yesterday. No voltage between the terminals for all four Motor terminals, but they all have voltage measured across their GND and one of the their terminals.
Thank you.
Attachments
back_3_18_13.JPG (160.38 KiB) Viewed 352 times
wzchang

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Joined: Sun Feb 24, 2013 7:16 pm