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From: philip@axis.fr (Philip Peake)
Newsgroups: sci.electronics
Subject: Re: NICADs
Message-ID: <284@axis.fr>
Date: Tue, 25-Aug-87 11:12:33 EDT
Article-I.D.: axis.284
Posted: Tue Aug 25 11:12:33 1987
Date-Received: Wed, 26-Aug-87 07:10:50 EDT
References: <8708040222.AA14785@ucbvax.Berkeley.EDU> <646@gec-mi-at.co.uk> <1619@sol.ARPA>
Organization: Axis Digital, Paris
Lines: 41
Summary: Two sets of nicads ?

In article <1619@sol.ARPA>, ray@cs.rochester.edu (Ray Frank) writes:
> 
> Finally, does any one know of a reliable way to determine how much charge is
> left in a nicad?  For example, I can safely fly for about 120 minutes on one
> charge before bringing it in and recharging it.  As the battery life decreases
> this 120 minute figure will decrease also.  I have measured my fully charged
> nicad pack at 5.2 volts (4 AA) and after about 2 hours they are down to around
> 4.8 volts.  But they will still read over 5 volts even after 90 minutes of 
> flying so they begin dying all at once and this can be dangerous when 500 feet
> in the air.  I bring the plane in every 45 minutes or so to check the voltage.
> By the way, I fly slope gliders and if my neck and batteries held out I could
> keep one up quite easily the entire day so you can see it is important to
> monitor the nicads and it is also nice to be able to charge the nicads from
> your car battery rather than leaving the hill for the day and waiting 14 hours
> for them to charge.

I am new to the RC aircraft game, but I must admit that the same thoughts
have occured to me - I also would be most upset to see my aircraft either
nose dive into the ground, or to fly away into the distance until its
fuel was exhausted (it would probably go a long way ...).

One Idea I did consider, having found no way to tell how much charge is left,
would be as follows:

	Put a second set of NICADS, (actually two sets, one for the
	servos, and one for the radio), together with a small voltage
	measuring circuit which would be responsible for switching in
	the second set when the first failed. It would also have to
	give some indication, since I would use much smaller capacity
	cells for the backup.

	As a warning, I thought of placing a xenon tube (small camera
	type) somewhere on the underside of the aircraft, and this
	would start to flash - it should be visible even in daylight.

I suppose that this is only possible if you have extra carrying capacity
in the aircraft - for a glider ?

Any better ideas would be welcome.

Philip