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Message-ID:	<4EF2343D.10601@ecosensory.com>
Date:	Wed, 21 Dec 2011 13:32:13 -0600
From:	John Griessen <john AT ecosensory DOT com>
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To:	geda-user AT delorie DOT com
Subject:	Re: [geda-user] Design suggestions...
References:	<CALSZ9godJsJDhBd_PaCiWPx9M8GyKz8PW1wVUs6NxVgtrOS-Fw AT mail DOT gmail DOT com> <201112211816 DOT pBLIGsaf016475 AT envy DOT delorie DOT com> <4EF229B4 DOT 8050008 AT ecosensory DOT com> <201112211909 DOT pBLJ9GKo018193 AT envy DOT delorie DOT com>
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Reply-To:	geda-user AT delorie DOT com

On 12/21/2011 01:09 PM, DJ Delorie wrote:
> I'd assumed rotor inertia would be sufficient, but I suppose "that
> depends" as usual.

I'm sure the inertia is plenty to keep it going.  The smoothing can be good if the motor
inductive response of the bare motor makes big volt spikes between
times it is driven by transistors.  A series wound brush DC motor with some added
capacitance at the motor, downstream of the FET switches will be less noisy,
less likely to have a big volt spike if run hard then cut off.

On 12/21/2011 01:16 PM, John Doty wrote:
 > The problem with added capacitance is that it increases the dissipation of the driver, since it then has to charge/discharge 
the capacitors when it switches. With enough capacitance to smooth the waveform, this will be a big effect.

I'm suggesting capacitance enough to make the PWM square wave disappear, not round its edges.
and it's at the motor.  When the FETs cut on they just have to top up the voltage the cap stored since
last time.

This probably needs a sketch to help more.

John

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