anti-phase" mode which means that full on one direction is 0 and full on
the other direction is 127 I think that you said. Somewhere around 64
it isn't turning at all. It is no surprise that the two motors have
slightly different speeds at the same PWM setting, most cheap motors
will be like that - You'll spend a lot to a matched set, or you might
get lucky. you can always simply disable the chip when you want the
motors to stop and that takes care of the "wandering" null point.
Locked anti-phase works great for servos, but I don't like it much for
robot motors. They will respond very quickly because the current is
already flowing, but you suck the battery dry because you are pretty
much always pulling the same current, no matter what the speed is. Does
it have the signed-phase operating mode? That will be more power efficient.
DLC
Shaggy wrote:
> I have a Sabertooth. We discussed that months back, but once I got it, and
> began playing around with it, I found that the speed value that corresponded
> to off was a fairly vague point in the middle of the range from 0-127. In
> fact, the point seemed slightly different for the two motors, and even when
> the tracks weren't turning, the motors were humming, which I took to mean
> that plenty of current was flowing (I didn't test how much, but if there's
> noise, there's power), even at the point that the motors should have been
> stopped. This was while the Sabertooth was set in analog operating mode,
> which I believe is the right setting for use with PWM control.
>
> To get around this, I would need to use a relay to shut off power to the
> motors when they were not in use. Since they will not be in use for maybe
> half the time, I certainly don't want to be running their batteries down
> during that time.
>
> I actually need almost the same circuit with the Low-Cost H-Bridge, since I
> will need to disable the motors while the battery is charging, so the
> circuit isn't that big an issue. It is also possible that there is a
> different setting for the Sabertooth that would work other than the analog
> mode, but I haven't really gone looking very far. The Sabertooth is
> primarily targeted at the RC world.
>
>
>
> rtstofer wrote:
>
>> --- In oopic@yahoogroups.com, Shaggy <charrington@...> wrote:
>>
>>> There are so many posts, replies, and whatnot to this thread at this
>>>
>> point
>>
>>> (spread over several months, too), that I am getting lost in them.
>>>
>> Frankly,
>>
>>> I'm wondering whether I even quoted the correct piece in my original
>>>
>> post,
>>
>>> earlier today.
>>>
>> So, why don't we start over with a link to the H-Bridge and motor that
>> you actually have?
>>
>> Off hand, it seems close and you can't do anything about stall current,
>> that's what the motor will draw when it first starts rotating before
>> the motor starts generating back-emf.
>>
>> Overheating from long term running at 1A is likely but can be solved
>> with a heatsink. Stall current and the 2A limit is not usually
>> negotiable.
>>
>> Were it mine, I would opt for a much larger H-Bridge. Maybe the
>> Sabertooth 5A dual motor device.
>>
>> Richard
>>
>>
>>
>>
>>
>
>
--
------------------------------------------------------
Dennis Clark ooPIC Tech Support
www.oopic.com
------------------------------------------------------
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