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'(Semi-)[OT]:h-bridge'
1999\10\18@204116 by Christoph Klein

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Hi!

I'd like to control 2 class-600 motors in a track vehicle that are
driven at 6V. To enable a pic to do that I've built an h-bridge
using an L298, keeping close to a project by the DPRG:
http://www.dprg.org/hbridge.html
When I connect the motors to the battery directly they purr away
happily but connecting just ONE motor to the hbridge thing it will
run very slowly and the torque is all gone. The L298 on the other
hand doesn't get just warm, it'll sure heat up my cold winter
nights AND I can boil my eggs on it too.

All I changed was adding a +5v power supply with an L7805 which is
fed by the battery too (for the "logic supply voltage" of the L298
and the PIC that'll hopefully control all this). And I'm driving the
whole stuff with 6V instead of 12V as the DPRGsters do.
The current sensing inputs are connected to gnd directly. is THAT
a problem?

Any ideas? I'm nearly back to doing it with relays again ;)
Hey, that wouldn't be all THAT bad ... ;)

Christoph

p.s.: when is Tjaart expected back? we've all been real good,
honest ;)

1999\10\18@205151 by Sean H. Breheny

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Hi Christoph,

I'm afraid I'm not familiar with what "class 600" motors are. How much
current are you expecting them to draw? What is the stall current?

As it says in the DPRG page, the L298 can only handle about 1 amp. If your
motor needs more than that, then you need to go to something else (sorry if
I'm telling you something you already know, it's just that the project on
that page you sent us too involves EMULATING an L298 using discrete FETs.
The L298 itself cannot handle the 15 amps that they are talking about).

I'm not familiar with the current sense inputs (actually, I have never used
an L298 by itself). BUT, if they are intended to be floating (which they
very well might be, considering that an H-bridge creates voltages that
aren't meant to be GND referenced), then there could be a problem with
that,too.

Sean

BTW, I second what you said about Tjaart. I'm going to forward it to him...


At 02:39 AM 10/19/99 +0200, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
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1999\10\18@205404 by Sean H. Breheny

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>Christoph
>
>p.s.: when is Tjaart expected back? we've all been real good,
>honest ;)
>

Yeah, we have been good. Ever since Jory laid down the law and said that
the discussion better swing back to tech subjects. Tjaart?


|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
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1999\10\19@064821 by Christoph Klein

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Sean, You wrote:

Hi Christoph,

> I'm afraid I'm not familiar with what "class 600" motors are. How
> much current are you expecting them to draw? What is the stall
> current?

oops. quite a lot, really ;) it says here:
- operating voltage 3,6 to 8,4V (I've got 6V)
- No-Load value 2A (I was having NO LOAD ;) )
- well. okay, at max. efficiency it says something about 12A here ;)
- and "stalled" the current is a mere 85A ;)

anyway, under testconditions it should work as the specs for the
L298 talk about a peak current of 2.5A per channel "Non repetitive"
and 2A under DC operation.

> As it says in the DPRG page, the L298 can only handle about 1 amp.
> If your motor needs more than that, (...)

Under real operating conditions it does, I agree.
So back to relays, as I said ;). At least, with a little modi-
fication I have got myself a real sophisticated way of driving
the relays using my L298 device ;)


> something else (sorry if I'm telling you something you already
> know, it's just that the project on that page you sent us too
> involves EMULATING an L298 using discrete FETs.

> The L298 itself cannot handle the 15 amps that they are talking
> about).

I'm sorry, I posted the wrong URL. I meant:
http://www.dprg.org/l298.html (which does use real L298's but what
You said about the current is still true, of course).

> BTW, I second what you said about Tjaart. I'm going to forward it
> to him...

we could have a little campaign like "Save the whales":

"SAVE THE WALTS"

How 'bout that?

Christoph

1999\10\19@100344 by Andy Kunz

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>I'm afraid I'm not familiar with what "class 600" motors are. How much
>current are you expecting them to draw? What is the stall current?

Graupner (http://www.graupner.com) rates its motors this way.

A standard R/C car motor is a 540.

A lengthened 540 (about 1cm longer) is a 550.

Then comes the 600.

The 700 motors are about 50mm dia (I forget exact dimensions and I'm
working from memory).

I use a stock 700 in my models on 12 cells for sport use.  See
http://www.rc-hydros.com for how they are used.

Andy

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1999\10\19@135518 by Don Hyde

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I have another dumb question: Who makes the L298 and how much does it cost?

{Quote hidden}

1999\10\19@141009 by Sean Breheny

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Hi Andy,

Thanks for the info! I went to their site,but it seems to be only about
their models, not motors.

I do love how they have that little graphic "hear the fantastic Wankel
sound!" <G>

Sean


On Tue, 19 Oct 1999, Andy Kunz wrote:

{Quote hidden}

1999\10\19@150234 by John Mitchell

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On Tue, 19 Oct 1999, Don Hyde wrote:

> I have another dumb question: Who makes the L298 and how much does it cost?

ST Microelectronics http://www.st.com (used to be SGS-Thompson I think).

http://www.bgmicro.com/ has them for $3.49 (surplus)

http://www.questlink.com/ has *tons* of info, 3 different variations in
the $2-$3 range.  woo!


(I've been looking at the SN754410NE, which is used in the Rug Warrior,
and is a replacment for the L293; which is a lower-power version of the
L298.)


- j

1999\10\19@150451 by Andy Kunz

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>Thanks for the info! I went to their site,but it seems to be only about
>their models, not motors.

I haven't been there in a while.

hobby-lobby.com is the US importer.
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