Re: [oopic] H-Bridge issue...maybe.

That's good to hear. Just having something hooked up wrong is a much better
problem than faulty hardware. Now how to go about figuring out what it is.

I have gone back to the manual for the Rogue Robotics ATS, and confirmed
that my code is exactly the code they have: IOLineP is 17 for one, and 18
for the other. IOLine1 is 26 and 24 respectively, and IOLine2 is 27 and 25
respectively. There really isn't any more code other than that for setting
up the oDCMotor2. To run the motors, there is a countdown timer which is set
to a value in seconds. As long as it is greater than 0, the operate property
for each motor is set to true. When the countdown reaches 0, the operate
property for each motor is set to false. That's the extent of the code,
though it is not all in one place.

As far as hooking things up, I've also reviewed that. There is a ribbon
cable running from the OOPic to the Low-Cost H-Bridge (LCHB). This ribbon
cable is designed so that there is only one way it can be plugged in on each
end, and the ends are plugged in as required. If the cable is wrong....well,
I haven't looked at that.

There are two pads for external power, which are labeled + and -. I soldered
the red lead from the battery to + and the black to -. Simple enough. The
documentation then states that if external power is supplied, the jumper
should be moved closer to a named capacitor. I have confirmed that that is
set correctly.

The only other connection I have made is between the motors and the LCHB.
The documentation mentions color coded wires, which I can't actually do,
since these motors have different colors, but I followed the intention after
figuring out what the colors actually meant on the ATS motors.

If this is a ground issue, where does it lie? The LCHB is designed to be
hooked up a certain way, and it is. If the connections that are actually
needed are not the ones in the documentation, it's going to be a pain to
figure out what's wrong.

A couple things I'd have to look at are these:

1) Do the connections on the ribbon cable actually lead to where they should
lead? I think I don't necessarily need to test this, because it was working
(I think) with the ATS. I'm pretty sure I tried it with lower speeds, though
I was not using external power.

2) What does the jumper actually do? The documentation states where the
jumper should be, without explaining anything about what it does. Should be
simple enough to trace, though not so easy to get to the board anymore.

Is there anything else I should be checking out?

rtstofer wrote:
>
> --- In oopic@yahoogroups.com, Shaggy <charrington@...> wrote:
>>
>>
>> Ok, this morning I set up the bot so that I could measure the
> voltage to the
>> motors. When I set the motor speed at 127, the voltage across the
> motor pins
>> was 8.7, which is pretty reasonable. When I changed the motor speed
> to 120,
>> the voltage across the pins was just below 1. It held steady around
> 0.6V.
>> That's certainly a bit low for those motors.
>>
>> The second time I tested this, I got the same voltage at 127, the
> same at
>> 120, about 0.4V at 100, then I tried 126. The voltage first showed
> about 2V,
>> at which the wheels bumped forward some, but the voltage dropped rapidly
>> down to 0.8V.
>>
>> That's not a very smooth curve. Can you point me towards a solution?
>>
>
>
> What did you get at the OOPic pin?
>
> This sounds like the kind of thing that happens when the motor power
> supply ground wire is not connected to the logic ground.
>
> As discussed in another thread a couple of days ago, you need to
> create a STAR ground at the motor controller chip. The logic ground
> and the motor ground tie individually to that point. The objective is
> to keep motor ground current off of the logic ground wire.
>
> There is a wiring diagram for the L293D (a predecessor to the 754410)
> at the bottom of the oDCMotor2 object reference.
>
> Richard
>
>
>
>
>
>

--
View this message in context: http://www.nabble.com/H-Bridge-issue...maybe.-tf4867316.html#a13939029
Sent from the OOPic mailing list archive at Nabble.com.

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