Subject:
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Re: design alternatives: servo control and power source
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 16 Apr 1999 16:56:54 GMT
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Original-From:
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William Sitch <wsitch@engsoc.carleton.ca/ihatespam/>
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Viewed:
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1237 times
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Hi Doug:
I built a 12-servomotor walking robot using two SSCs - their interface
with the HandyBoard is well documented, and ICB drivers are available on the
webpage. I communicate with two SSCs (www.seetron.com) via one serial line
connected to PA7 - a digital input port - as documented.
The SSCs require a 9-volt supply, so I share the HandyBoard battery. I use
a rechargable NiCd battery, and to this point it hasn't required intentional
recharging. The SSCs also take in a 4.8-volt to 6-volt supply that is
pulse-width-modulated to drive the servomotors. In my experience, the
twelve standard motors (50oz-in) can draw 3A at 5V at stall - which is a
large amount of current.
If you have a large 9-volt supply to power the boards and the motors, the
servomotor current draw will spike and probably reset your control boards.
You could try to isolate the supply leading to your boards, but that would
be complicated and not completely effective. You'd also have to voltage
divide the large 9-volt supply, and this gets tricky - you'd have a
considerable loss over the voltage divider that would make this
unattractive. The number 15% comes to mind, but I can't back that up.
I used the one 9-volt NiCd for the HandyBoard and the SSCs, and a 4x1.2-volt
NiCd battery pack for the servomotors. As I mentioned, the motors peaked at
3A of current draw. In retrospect, I would have designed for double the
weight in batteries, and put four more NiCds in parallel for extended
operating life.
I hope that helps!
--
William Sitch, http://www.engsoc.carleton.ca/~wsitch
4th Year Electrical Engineering at Carleton University
----- Original Message -----
From: <doug@los-gatos.net>
To: <handyboard@media.mit.edu>
Sent: Friday, April 16, 1999 11:59 AM
Subject: design alternatives: servo control and power source
> Hello,
>
> I am planning to build a robot based on the Lynxmotion Hexapod II
> and Big Grip kits. There will be 12 servos for lego control, 2
> servos for the manipulator, and 2 more for a camera pan/tilt
> unit. Everything appears fairly straightforward, but:
>
> 1) I am trying to decide on whether to use two mini SSCs or the
> Ferrettronics chips to control the servos. Does anyone have
> any info/experience that might sway me one way or the other?
> Is anyone aware of documentation or tips for using either
> of these with the handy board?
>
> 2) I am wondering if I can run the servos from the handy board
> batteries or if I need to have a separate battery pack for
> the servos. Obviously the HB batteries won't last very long
> if they are also running 16 servos, but would this work?
>
> TIA,
> Doug
>
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