Alt-BEAM Archive
Message #00747
To: beam beam@corp.sgi.com, Steven Bolt sbolt@xs4all.nl
From: Sean Rigter rigter@cafe.net
Date: Sun, 21 Feb 1999 17:17:17 -0800
Subject: [alt-beam] stepper motors & MAN/WALKER
Hi Steven,
Yup, always add diodes. There are a number of other details missing.
Anyone actualy building one of these?
When using another FET make sure you select a "logic" FET that saturates
(ie Rds < .1 ohm) at MicroCore output voltage levels (~3V)
Cost?
There's a small selection of "workhorse" high current N channel
POWERFETs from IR, Motorola and others costing around $1. P FETS are a
little more. A 10 Amp POWERFET bridge can probably be put together for
$5-6.
Just what I need for my "hobby horse" walker 8^).
Actually I have a couple of 1/5 HP motors running off my 24V 4Nv
RELAYCORE which will do the job for the MAN/WALKER prototype. (you
should have seen the faces when I pulled out my relaycore and the 4 inch
diameter/ 6 inch long motor at the local BEAM group meeting).
Still have to use a manual PNC to get it out of saturation but the
single process is rock steady clicking away around the loop. I use 5K
8^) potentiometers for tuning each pair of Nv relays. I will be using
pulleys and v-belts for the "gearbox". Has anyone done a 2 or 3 speed
(or infinitely variable) transmission for BEAM motors? You switch gears
going up or down hill.
In case you are woried about a "foaming at the mouth" big walker on the
loose, my MAN/WALKER will be a study in fail-safety devices.
later
wilf
Steven Bolt wrote:
>
> On Sun, 21 Feb 1999, Sean Rigter wrote:
>
> > I suggest using 2N7000 N channel Power MOSFETs ($0.50 ea)
>
> Nice price... Somewhat difficult to obtain here, pity.
>
> ---8<---
> > since you can then use a high voltage (12V)
>
> I notice you left out Richard's diode. The 2N7000 might protest,
> depending on the coil.
>
> ----------------------------------------------------------------------
> # sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
> ----------------------------------------------------------------------
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