RE: (ET) motors

["Elie, Larry \(L.D.\)" <lelie ford com>]

My earlier stuff may have been missed.  Use a 12 or 14 V regulator (less 
than 
a buck) on each motor.  It won't go high, ever.  It has to be able to 
handle 
the current, so it isn't exactly trivial, but it isn't that hard either.

Larry Elie


-----Original Message-----
From: Christopher Zach [mailto:czach computer org]
Sent: Monday, June 14, 2004 11:56 AM
To: Elie, Larry (L.D.)
Cc: neil; elec-trak cosmos phy tufts edu
Subject: Re: (ET) motors


*Nod* Except for the fact that the other two motors are now spinning at 
4/3rd their RPM or faster. At a certain point the bearings will be 
overstressed, or even worse the blade will rip apart.

If you stall two motors for even the most innocent of reasons (say 
cutting grass in a strip) motor 3 will go to 9,000 or so RPM. That will 
be bad. Also I am not sure how three motors would brake down when 
shorted; remember that is an important feature in the Elec-Trak, the 
blade really has to stop spinning within a second or two.

I think the design of some DC-DC converters is the way to go here. I'm 
going to work on a 24 volt one, I see no reason why we can't just build 
a module to convert 36 volts down to 12 volts for the deck motors. Only 
problem is the current requirements go up by a factor of three. Braking 
could be addressed with a crowbar relay attached to a capacitor and a 
low voltage detection sensor.

Chris
> You are right, but that is a SAFETY FEATURE.  Most cutting involves the 
> inertia of the motor.  
> It is turning 3,000 RPM.  If the resistance is brief, a fraction of a 
> second, the change in 
> speed is small.  If you hit something, you WANT IT TO STOP.
> 
> Larry Elie