Motorshield, Stacked SN754410, and Steppers, Oh My!

Adafruit Ethernet, Motor, Proto, Wave, Datalogger, GPS Shields - etc!

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adafruit_support_bill
 
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Re: Motorshield, Stacked SN754410, and Steppers, Oh My!

Post by adafruit_support_bill »

At this point I would suspect either a problem with your piggyback assemblies, or the motors themselves are pulling too much current. Plug the chips back in, but disconnect the motors. Does the problem come back?

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tessierashpool86
 
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Re: Motorshield, Stacked SN754410, and Steppers, Oh My!

Post by tessierashpool86 »

adafruit_support_bill wrote:At this point I would suspect either a problem with your piggyback assemblies, or the motors themselves are pulling too much current. Plug the chips back in, but disconnect the motors. Does the problem come back?
I will try this tonight.

Since we know the power supply, the chips and the resistance of the motors, can you tell me which of these is not correctly matched? I believe I should have enough headroom with two sets of stacked SN754410s.

DC (5V @ 2000 mAh) -> 2x2 H-bridges (4A) -> 2 Steppers (4.1 ohm ea @ 5V = 2.44 A)

Am I off in my math for the power draw of the motors because I'm not taking into account the second phase? If anything, it seems like the power supply should be getting overloaded, but I don't see how that would cause connectivity issues with the arduino (which is using USB).

Bottom line, even if something is out of whack here, why is it causing the USB port to shutdown?

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Re: Motorshield, Stacked SN754410, and Steppers, Oh My!

Post by adafruit_support_bill »

No. Remember I've got the motor shield powered by a 5v 2000mah dc adapter. The jumper is definitely out.
If you are powering the motors via an external supply with no VIN jumper, there is no reason that the USB should be overloaded.
Since we know the power supply, the chips and the resistance of the motors, can you tell me which of these is not correctly matched? I believe I should have enough headroom with two sets of stacked SN754410s.
So far, we are assuming that the motors are 4.1 ohms/phase. Have you measured to confirm?
Doing the math, 5v - 1.2v drop through the bridge = 3.8v to the motor. @4.1 ohms/phase, that would be .93 amps/phase. Times 4 phases, that is 3.7A. Based on those assumptions, your power supply is too small. But that doesn't explain the USB problem.

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tessierashpool86
 
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Re: Motorshield, Stacked SN754410, and Steppers, Oh My!

Post by tessierashpool86 »

adafruit_support_bill wrote: So far, we are assuming that the motors are 4.1 ohms/phase. Have you measured to confirm?
Doing the math, 5v - 1.2v drop through the bridge = 3.8v to the motor. @4.1 ohms/phase, that would be .93 amps/phase. Times 4 phases, that is 3.7A. Based on those assumptions, your power supply is too small. But that doesn't explain the USB problem.
No, I haven't measured. I will do that tonight.

I also don't know that it is 4.1 ohm/phase. It just has a sticker on the side with 4.1 ohm. See below:
img_2007-1.jpg
img_2007-1.jpg (56.76 KiB) Viewed 854 times
Given that the power supply might be too small, that would just make it run hot and potentially burn out, right?

Are there any weird side effects from using different h-bridge chips that could cause flakiness with the arduino? Any known issues with the v1 motor shield where it can cause issues with the arduino?

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Re: Motorshield, Stacked SN754410, and Steppers, Oh My!

Post by adafruit_support_bill »

Given that the power supply might be too small, that would just make it run hot and potentially burn out, right?
Depends on the power supply. On some, the voltage output will drop. Others will shut themselves down to prevent damage. And there are those that will either burn up or burn out.
Are there any weird side effects from using different h-bridge chips that could cause flakiness with the arduino? Any known issues with the v1 motor shield where it can cause issues with the arduino?
I've been running SN754410s, both piggybacked and plain, on a couple of my boards for several years now. I have never had a problem with them, or heard of one here on the forums.

USB overload conditions can be caused by trying to power motors from Arduino. But you are using an external supply. If there is no USB overload condition, there is likely a problem in your piggyback assemblies. Make sure that all pins are cleanly soldered with no bridges. And make sure that the heat-sinks are not shorting out against any of the pins.

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Re: Motorshield, Stacked SN754410, and Steppers, Oh My!

Post by tessierashpool86 »

adafruit_support_bill wrote: USB overload conditions can be caused by trying to power motors from Arduino. But you are using an external supply. If there is no USB overload condition, there is likely a problem in your piggyback assemblies. Make sure that all pins are cleanly soldered with no bridges. And make sure that the heat-sinks are not shorting out against any of the pins.
That's a good point. I'll double check the soldering and might pull off the heat sinks since I can replicate the issue fairly quickly.

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Re: Motorshield, Stacked SN754410, and Steppers, Oh My!

Post by tessierashpool86 »

adafruit_support_bill wrote: And make sure that the heat-sinks are not shorting out against any of the pins.
I'm pretty confident that this is the problem. I took off the heat sinks and could not replicate the error.

Any advice for the best way to keep those heat sinks centered? I'm thinking about stuffing the some thinly folded paper stents in between the leads and the metal of the heat sink to keep it from shorting the pins. Those heat sinks have a tendency to slide around a little when you press on them to get the chips in place.

Thanks for the help, Bill. I'm super excited to get this working.

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Re: Motorshield, Stacked SN754410, and Steppers, Oh My!

Post by adafruit_support_bill »

You can use something like this: https://www.adafruit.com/product/1467
or a two-part thermal adhesive instead of thermal grease to hold them in place.

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