Alt-BEAM Archive
Message #10664
To: beam@sgiblab.sgi.com
From: Ben Hitchcock beh01@uow.edu.au
Date: Wed, 23 Feb 2000 07:53:10 +1100 (EST)
Subject: [alt-beam] Re: Walker problems
Hi,
> Well, I finally bought the RC servos for the walker the other day and for
> some reason, they are just don't work....once in a while, they might turn a
> couple of times, then the gait becomes fully saturated and the motors stop.
Sounds like you need a 0.1 uF cap across the power leads of the chip.
This should stop the saturation.
> The next thing that happens is that they just barely 'click' when they are
> suppose to be on, with not actual movement. I even stacked up to 4 of the
> 74HCT245's, but that didn't work either. (I couldn't get my hands on the
> 74HC245's...which might be the cause of the problem.)
This problem sounds like the servos are at the limits of their travel.
Once you gibve the bot legs, the servos should 'auto center', providing
you don't stack too many chips. Try centering the servos and seeing what
happens.
> Without the motor's,
> the circuit works great. With the cheap motors that I got surplus (just for
> the sake of trying the circuit out), they work well with two of the
> 74HCT245's stacked. Now when I stick on the servo's, they just either don't
> work, or they go into fully saturation and then they don't work. The
> servo's drink about 150 mA's, which should mean I could stack 3 or 4 of the
> 245's and be in the clear by far. I am going to try to get some of the
> 74HC245's, (which I think have a wider range of input voltages.) The 7805
> didn't change anything, so I didn't try that for long. Any ideas on what I
> can do? Is it common for servos to use that much power? How many of the
> 245's can I stack? Is there something I can use that's not the 245, that
> can handle higher load? Is the H-bridge something I should be looking at?
> Take care and thanks in advance!
> Bernie
hth,
Ben
10665 Mon, 21 Feb 2000 16:01:46 -0800 [alt-beam] Re: Ic chips "Dennison Bertram" Oh you definitly have to use a 74hc245. You can use other varients of the
74xx245 series, but they have to be the same type of chip. There are
thousands of varieties of ten pin chips, all of them do something very
different.
dennison
> I am working on a walker but can't find the 74HC245's
> that I need for the master-slave setup. I was woundering,
> Could I use any ten pin DIP IC chip for the setup or does it to be
> a 74HC245 for it to work?
>
> thanks
> Mark
>
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