home *** CD-ROM | disk | FTP | other *** search
- Path: sparky!uunet!elroy.jpl.nasa.gov!nntp-server.caltech.edu!tod
- From: tod@cco.caltech.edu (Tod Edward Kurt)
- Newsgroups: rec.models.rc
- Subject: Re: Question About Speed Controls.
- Date: 20 Nov 1992 21:57:00 GMT
- Organization: California Institute of Technology, Pasadena
- Lines: 37
- Message-ID: <1ejmvcINN85u@gap.caltech.edu>
- References: <92325.123603IO10046@MAINE.MAINE.EDU>
- NNTP-Posting-Host: sandman.caltech.edu
-
- <IO10046@MAINE.MAINE.EDU> writes:
-
- > I have a question about the operation of speed controllers.
- >What is ment by high frequency speed controls? I known that they
- >are supossed to be better for the motor and its brushes but why?
- >Does it reduce brush arching? What does the output of a controller
- >look like? Maybe:
-
- > ---- ---- ---- 7.2V
- > | | | | | |
- > | | | | | |
- > ---- ---- ---- --- 0.0V
-
- > What is the frequency? In the KHz?
-
-
- >Aaron Brasslett
- >University of Maine
-
- I can't think of why exactly it's better for the motor (execpt maybe
- that it's always being driven at the same voltage, but that's pretty
- much exactly what it looks like. Typical ESCs run around 2500Hz and
- pulse the motors with a varying duty-cyle square wave. The advantages
- of this are higher torque over entire speed range (since instantaneous
- current and voltage are constant) and cheaper power transistors can be
- used. It's also much easier to control. From talking to various
- manufacturers of these things, it sounds like most of them just take
- the brains out of your typical $11.99 servo, fix the feedback
- resistor, and add power mosfets to drive the motors differentially.
- I'm working on an ESC of my own right now, but I'm having a hard time
- finding chips that are still in production (@$&!! old spec books!)
- The ESC makers also add goodies like regeneration (recharges your
- battery and brakes at the same time!) and a torque control. These I'm
- still working on. You trying to design your own?
-
- -Tod
-
-