drawing too much power with the current setup, and will just cook the chip
in short order. I can't guarantee sufficient offtime for the chip to cool
back to ambient, so it ought to fry eventually, especially if the motor
stalls and overloads the thing.
ooPIC Tech Support wrote:
>
> I don't see any mention either - It should say if it was defaulted to
> something specific. If not I'd assume that it was where the oPWM object
> was, which was like 20KHz, WAY too high for the 754410 motor
> controller. Check out the oPWMH specs and see what it takes to move
> that down to 1 or 2KHz and see if that changes things.
>
> DLC
>
> Shaggy wrote:
>
>>Off the top of my head, I don't know. However, I would expect that would
not
>>be an issue since the LCHB is sold by RogueRobotics to go with their OOPic
>>board. I would not expect them to be including the LCHB if it won't work
>>with the board they are using. I believe it was working as expected when I
>>had it attached to the ATS motors, which are smaller than the Robotics
>>Connection motors I am currently using.
>>
>>I'm leaning towards too much power draw. I'll try to look at that this
>>evening. The motors can certainly draw too much power for the LCHB, so it
is
>>looking like I will have to replace that, regardless of whether that is my
>>specific problem. After all, the 754410 is getting a bit warm, even with a
>>heat sink, when I run the motors for 10s.
>>
>>Therefore, if anybody has a recommendation, I'll take a look at it.
>>Otherwise I might just go with the H-Bridge sold by the same company that
>>sold me the chassis and motors. I'm pretty sure that one will take enough
>>power, though I will still have to look it over some.
>>
>>
>>ooPIC Tech Support wrote:
>>
>>
>>>What is the frequency of your PWM? The 754410 is happiest at 2KHz or
>>>lower. At 20KHz I've detonated these chips!
>>>
>>>DLC
>>>
>>>ooPIC Tech Support
>>>
>>>-----Original Message-----
>>>
>>>From: Shaggy <charrington@idfg.idaho.gov>
>>>Subj: Re: [oopic] H-Bridge issue...maybe.
>>>Date: Sun Nov 25, 2007 12:38 pm
>>>Size: 4K
>>>To: oopic@yahoogroups.com
>>>
>>>
>>>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.
>>>
>>>
>>>
>>>
>>>Yahoo! Groups Links
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>>
>
> --
> ------------------------------------------------------
> Dennis Clark ooPIC Tech Support
> www.oopic.com
> ------------------------------------------------------
>
>
>
> [Non-text portions of this message have been removed]
>
>
>
--
View this message in context: http://www.nabble.com/H-Bridge-issue...maybe.-tf4867316.html#a13976913
Sent from the OOPic mailing list archive at Nabble.com.
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