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Radio - JR & Spektrum DSM > Some thoughts on regulators and nicads....
 
 
nivlek
rrProfessor
Location: Norfolk England

Climax , OK .
One farad is good for 1 amp at one volt for 1 second .
You can easily place a large load on the servos in a heli for that period of time . Why do you think that the capacitor available from Spektrum is only recommended for cars ? Is it not because cars only have one servo under high load and that they are unlikely to sustain that load for more than just extremely short periods ?
Five farads was just a figure off the top of my head , but the point is still valid .

At the end of the day , it gets dark .
06-14-2008 12:04 AM
 
 
Climax
Veteran
Location: West London, United Kingdom

I do tend to go on a bit about the nano phosphate A123 cells! They are just so good...

On the subject of super capacitors, these are the basis of the Fromeco DCUP. This has a capacitance of 1.66F, for details see:

http://www.fromeco.org/Products/05FRCDCUP/Default.aspx

I've got one for my Trex-500 as I don't trust the Align built-in BEC. I hoping that it will help to smooth out any BEC generated noise, and also deal with any momentary drop outs.
06-14-2008 07:51 AM
HOMEPAGE  
 
 
pchristy
Senior Heliman
Location: Nr London, England

Rexxigpilot
Quote 
pchristy, you ever hear of a capacitor? .....

To work effectively as a smoothing device, a capacitor needs an associated resistor - this provides a time constant - and resistance is precisely what we DON'T want here!. A capacitor big enough to be effective on its own at the kind of voltages and current draws we are talking about would have to be HUGE! It simply isn't practical!

A choke is effective at suppressing the high frequency garbage coming down the supply lines. However, a choke capable of handling the current of up to 5 digital servos would again be quite a monstrosity! It would also prevent the servos from drawing current suddenly, which I'm not sure would be a good thing!!!

The only place the choke/capacitor solution will work is if they are placed AFTER the supply to the servos, but BEFORE the supply to the receiver. This means building it in as an integral part of the receiver - not an external, add-on goody!

Re: your comments about old fashioned batteries.

There is something in what you say. Unfortunately many of the servos currently in use are unsuitable for use on the higher voltages provided by lipos. When manufacturers start designing ALL their equipment for use at these voltages, things will get a lot simpler! In the meantime, we have to work with what we have. My experience - and that of others as well - indicates that regulator/lipo set-ups are as likely to be the source of the problem as the cure!

--
Pete
06-14-2008 02:40 PM
 
 
pchristy
Senior Heliman
Location: Nr London, England

Maveric4:
Quote 
currently use 2000mah sub C sanyo cells but I am finding because of the high draw from as you said digital servos I am only able two manage 2 flights with the third being questionable before a recharge as I am using 480ma per 20 min flight.

I am considering buying some Tornado 4300mah sub C NiMi packs.


As a general rule, NiMH cells can't handle such high currents as NiCADs, however, cell technology is fast moving, and modern NiMHs are much more capable than those of only a year or two ago. With the high capcities you are suggesting, I would expect them to be able to handle the current, but I don't have any first hand experience of these particular cells.

NiMHs do tend to self-discharge a lot more than NiCADs, so don't charge them and then leave them a week before flying! Either slow charge overnight before flying, or fast charge in the morning before you go to the field!

The general rule for NiCADS is to discharge them to 1.1 volts per cell before storing them.

The memory effect is not as serious as many make out and is easily reversible! What happens is that thin whiskers of crystals form in the electrolyte and grow across from one electrode to the other. When they go right across, the cell shorts out, and you get zero volts! Upto that point you get reduced capacity!

The cure is to charge briefly at very high current to melt the whiskers! NOTE: ONLY DO THIS WITH VENTED CELLS, NOT SEALED ONES! If you overdo it, the cell can burst quite violently, so only do this AT YOUR OWN RISK!

I've unstuck pen-cells before now by very briefly flashing them across a 12 volt battery whilst monitoring the voltage. It will suddenly ping up to its nominal 1.2 volts, and you can then charge it normally!

Nicads seem to last better if they are subjected to heavy current draw and charging - provided you don't let them get too hot (which dries them out)! Its always packs that are treated gently that seem to fail first....!

--
Pete
06-14-2008 03:02 PM
 
 
nivlek
rrProfessor
Location: Norfolk England

These are the nimh cells that I now have in my helis .

http://www.gpbatteries.com/pic/300schR%20rev1.pdf

They have a low impeadance so their volt drop under load isn't bad . It's nice to know that they can deliver 30A , even although I hope that I never draw that much !

Here is their range of cells .

http://www.gpbatteries.com/html/techinfo/nimh.asp

At the end of the day , it gets dark .
06-14-2008 05:40 PM
 
 
MikeInMobile
Key Veteran
Location: Mobile, Alabama

Modern switching regulators work WELL on helicopters, so long as an integral capacitor is present. The capacitor doesn't need to be that large, only 500 uF will prevent surrent spikes from creating an oscillation. The output of a switching regulator is inductive by nature, so a relatively small capacitor is required to obtain excellent filtering and stability on the regulator's output.

A general rule of thumb is to get a regulator that can continuously supply 2 times the amount of current required by all of the servos when in NORMAL operation. This allow enough current overhead for the spikes during extreme maneuvers.

I have found that regulators make the control of the servos much more consistent than when Nicads or NiMh are used.

A general rule of thumb is to use a regulator that can supply at least 5 amps of continuous current if you are using digital servos, or a regulator capable of at least 3 amps is you are only using a digital tail servo.
06-14-2008 10:10 PM
 
 
Heliguychris
Senior Heliman
Location: Perth, West Australia

So,, what ya saying Pete, is if ya having dramas with ya regs, etc,, its not the end of the world, juss whack back in a tough ole nicad pack, and start again. Hope so,, cause thats what i tell anyone who`ll listen

Ive been using the Dualsky reg, in my 90s, with 2500 mah evo lites, with exellent results. It seems to be able to handle high current servos such as Hitec5955tgs, no problems.
My average amp draw, must be pretty high, cause for about a 5 min flight, in a vibe, ill use 320/370 mahs, per flight.

Cheers for the other info here, like the wiskers, in old bateries. Ive always known a short, high current, voltage, will sometimes bring em back to life,,,, but neva knew why,, but now i do

Salutes`

Chris.
06-15-2008 12:26 AM
 
 
pchristy
Senior Heliman
Location: Nr London, England

MikeInMobile: Like I said in my original post, if a regulator is working fine for you, then carry on! For some people they work without any issues! BUT - if you are getting glitching, and there is no obvious physical cause (loose parts, frayed leads, etc) then the first thing to check should be the regulator! And the best way to check it is to replace it with something simpler, and that most people will have lying around!

Heliguychris: Yes - see my answer above! You've been handing out good advice! Glad to have been able to explain the "shorted nicad syndrome"!



--
Pete
06-15-2008 08:26 AM
 
 
SniperKitten
Heliman
Location: Wiltshire, UK

What a great, educational, thread.

A few years ago, I did some lab studies of batteries for UAVs and found what an awful lot of vodoo and myths are in your average modeler's minds. Such as Memory Effect.

About 2 years ago, I charged my 6 month old NiMH pack in my TX and drove 20 minutes to the flying site. When I got there, the battery was completely dead. So, to add to the list of bad things about NiMHs, I added that they do not degrade gracefully, i.e. slow reduction in capacity, they can just die suddenly.

I threw out all of my NiMHs and will not use them in any modeling application.

The next step was to look at alternatives, including Lithiums and regulators. Having studied reliability engineering, I started to get wary. KISS!

In the last 9 months or so, I have been buying NiCad packs. I have one RX pack on my bench that is 20 years old. It has reduced in capacity about 20% but is still useable for setups. Now, I take spare RX packs for my helis when I go to fly them.

I always try to slow charge my batteries. The reason is the same as that for 'forming charges'.

http://www.rcbatteryclinic.com/

http://www.batteryuniversity.com/

Unfortunately, the crooks, cretins and crisis creators in Europe who call themselves 'politicians' have decided to ban NiCad sales in Europe (at least) from this coming September. I have a box full of NiCads which should keep me going for a few years.

Regrettably, I cannot do anything about C^4 except shout at them when I see them on the TV!
06-15-2008 09:50 AM
 
 
MikeInMobile
Key Veteran
Location: Mobile, Alabama

I always "de-glitch" my machines using NiCads, but then switch to LiPo and regulators for regular use. When a machine is put into service, or repaired, everything needs to be checked for a possible source of glitching! A lot of people have switches to a DSM system because of glitching, but the actual source of the glitching is either mechanical in nature, or is caused by the routing of the wiring in the model. Both of these are easily correctable once identified, although, the identification process can often become time consuming. I use a FM system for initial setup and de-glitching of new systems, and often use a FM system whenever a repair is made.

As far as switch assemblies, I make my own using 18 gauge wire, gold connectors, and 10 amp mini-toggle switches. I have found that in a lot of cases, the power issues are due to the switch harness, not the actual power system. I also find that the toggle switches seem to hold up better than the slide switches.
06-15-2008 02:27 PM
 
 
pchristy
Senior Heliman
Location: Nr London, England

Funny that! I seem to recall back in the 60's. when I first got into RC, the standard advice was to use toggle switches! If you turned up with a slide switch, there was a collective sharp intake of breath!

The only slide switch I had a really high regard for was the Japanese Noble switch - alas, no longer made! I still have a few kicking around. They were real high quality jobs, with a positive "snap" action. Also, they were 4-pole changeover switches, so you could parallel up for extra current handling/reliability!

These days, we just get what we are given by the manufacturers! I have to say that the heavy duty JR harness holds up well, but I'd be a lot happier if they still used the Noble switches!

Hey Ho!

--
Pete
06-15-2008 04:57 PM
 
 
MikeInMobile
Key Veteran
Location: Mobile, Alabama

The JR heavy duty harness is EXCELLENT, but the cabling is only 20 gauge. I used to use the JR heavy duty harnesses before I started making my own. The toggle switch is a lot easier to activate in cramped quarters than a slide switch. The only helicopters that I still use a slide switch in are my Hawks. I opted to use a slide switch in them because I have a switch extension for activation.
06-15-2008 05:01 PM
 
 
danthemancarol
Heliman
Location: charlotte,nc

Ok, now I am confused

What an interesting thread. Most of you obviously have alot of talent and knowledge. I found this thread because I am thinking about swithching from nimh to a fromeco arizona. My buddies tell me they feel safer with lipo batteries because of the power drain, they also fly many more flights. Right now I have 2 nimh of 3800mah, I have a voltage checker and usually run 2 solid flights (voltage meter says "good range" after 2). So with 2 packs, roughly 6 flights and with the price of fuel these days who needs much more. Can anyone just say-----hey, this is the best? If I dont need the regulator and lipo, then I will just stay with what I use. Helis are just so expensive if you crash I want the best option.

If you were able to read and understand this, a post for a newbie would be great. thanks in advance
08-04-2008 11:31 PM
 
 
MikeInMobile
Key Veteran
Location: Mobile, Alabama

LiPos will give you more flights, and will perform better when they are NOT charged right before flying. As far as being "safer", using a regulator will make your voltage monitor (VoltWatch) totally worthless. The Voltwatch will only measure the output of the regulator, not the input voltage. You CAN get regulators with input voltage monitoring, but they are a bit more expensive than those without the monitoring logic. Also, since there is not a large load on the LiPos, you need to keep track of the capacity that you use out of the batteries. If you take too much out of the battery, you can seriously damage the LiPo.
08-04-2008 11:59 PM
 
 
billrad
Senior Heliman
Location: Rineyville, KY

some of my older flying buddies used toggle switches instead of slide switches.

If someone is motivated, post a picture of a toggle and wiring diag for your heli.

thanks

billrad

I may not be able to turn a kit into a plane, but I can turn a plane into a kit...
08-08-2008 03:34 AM
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Radio - JR & Spektrum DSM > Some thoughts on regulators and nicads....
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