Pololu motor controller buyer beware

Well I'm not thinking in any "particular" timescale. As mentioned in my other post and as others have also mentioned and as the technical support
person has told me given the motor specs, the transient occurs for a very short period of time and is not likely to cause the problem.
I also tried ramping up slowly from low speed to high. It has 127 speeds. Same problem, starts out spinning fine but as speed comes up it shuts off. Two different motors, (not same model) but similiar electrical specs. Tried heatsink and fan, runs a little longer but still shuts off. I'm beginning to think they probably just sent me back the first one that I was having problems with since I agree with Gordon that two bad boards are unlikely. I even hooked up the H bridge output to a scope amd can view the pulses shutting off and on repeatedly. I'm just going to design my own at this point and I already have an AVR programmed and ready to provide the PWM for a suitable driver so if you'd like to buy this one for a small project, let me know.
-Dave

drawing
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From the picture on Pololu's website, it appears that this board uses the TI driver SN754410 http://www.acroname.com/robotics/parts/R6-754410.pdf which is rated (max) for continuous output current of 1.1A.
One point to note is that this driver has both a Data supply (4.5 - 5.5V) and a motor supply (4.5-36V). If the data supply exceeds 5.5V my guess is that the driver logic will overheat and send the chip into thermal shutdown - but I'm sure you didn't make that mistake.
Kevin
"Rylos" <unknown> wrote in message

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Try www.acroname.com
Go to their "Drivers" section.
3A Low Voltage H-Bridge 3A Back EMF H-Bridge
They are more expensive than what you were spending, but at least they work as specified.
These can be used with your own controller, or with Acroname's MOTO board.
--Jay
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On Tue, 14 Sep 2004 17:43:39 -0400, "Rylos" <unknown> wrote:

There is one other possibility that I haven't seen anyone else mention. The issue is, the device may be working fine, doing a thermal shutdown when it gets hot, but if you don't have a heat sink, then the chip can't get rid of the heat that it's generating fast enough.
Many packages can generate more heat than they're able to dissipate without a heat sink and since you're using somewhat near the upper limit of its capabilities, it may require a heat sink to work properly. One way to see is to check the specs for the chip and see if they suggest using a heat sink. Sometimes, they'll tell you the maximum heat dissipation for a particular package and you may be exceeding it.
I don't know whether this is the case, I'm just offering a possible explanation.
Cheers, Ed L
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Thanks Ed, but I tried that to. Using both a heatsing and a fan. It's runs a little longer, but still shuts down.
-Dave

it
The
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On Thu, 16 Sep 2004 12:42:48 -0400, "Rylos" <unknown> wrote:

What voltage and current, precisely, were you using? Looking quickly at your earlier posts, it looks like:
    Average         Voltage: 5 Volts         Current: 250 milliamps     Peak         Voltage: 5 Volts         Current: 2 Amps
First, I would say that Polulu's documentation is lacking because they neither state the maximum power dissipation or the chip they're using (so you could look up the power dissipation).
However, guessing that the chip is an L293-class chip (which includes the SN754410), then the maximum continuous dissipation is 2075 milliwatts. Based on the figures above, this gives:
    Average Power = 5 * .250 = 1250 milliwatts     Peak Power = 5 * 2 = 10 watts
My view is that Polulu needs to enhance their documentation to state either the maximum power dissipation or the chip they're using. If one went merely off their current specifications, one might think that one could use up to 9 volts at 2 amps (for 18 watts); this would far exceed the specification for these kinds of chips. Maximum power dissipation is a requirement for properly using the chips.
Cheers, Ed L
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Hi Ed,
The 5V and 250mA are the precise values. The current was the steady state, no load current draw. I completely agree with you about their documentation being very lacking. The device, at least mine appears to do everything it's supposed to as far as the control and PWM goes, it just can't drive nearly as much amperage as they claim and that's been my whole gripe, maybe I just got a bad one. A motor controller that could handle 1A continuous per channel would be more than adequate for my next robot but my board doesn't come anywhere close to the rated specs. Either de-rate it, or be more explicit in the datasheets about device performance characteristics. Maybe, just maybe this thing could drive a pager motor.
-Dave

runs a

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One other thing that I haven't seen mentioned yet. Do you have noise suppression capacitors on your motor. Normally this is important for proper H-bridge operation. You should have a 0.1 uF cap between the motor leads and a 0.1 uF cap between each of the leads and the motor's case.
BRW
On Tue, 14 Sep 2004 17:43:39 -0400, "Rylos" <unknown> wrote:

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On Thu, 16 Sep 2004 21:06:24 -0400, Bennet Williams <> wrote:

One other thing that might be required is back-EMF diodes. L293's (at least the variant whose documentation I examined) don't have back-EMF diodes built into them. If Polulu didn't add them (assuming they used L293's), then back EMF could have caused a problem as well.
Cheers, Ed L
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Hi Bennet,
Good advice and yes I did that too but it had no effect on performance.
-Dave
<Bennet Williams> wrote in message

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