And if it doesn't have a heat sink, put one on it, a BIG one. The rated
current is only under idea circumstances which pretty much mandates a
heat sink to cool the chip.
DLC
Shaggy wrote:
>I should try that before getting a different H-Bridge, but I suspect that I'm
>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]
>>
>>
>>
>>
>>
>
>
>
--
------------------------------------------------------
Dennis Clark ooPIC Tech Support
www.oopic.com
------------------------------------------------------
[Non-text portions of this message have been removed]
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