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Freezeing your robot!
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Windhammer



Joined: 19 Jun 2004
Posts: 338
Location: Roleystone WA


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Freezeing your robot!

hello everyone

before i drive my remote control car around i stick it in the freezer for about 1hr. I do this because its makes all the wires cold and lets electrons pass through them much faster and it makes my car go about 5km faster. this affect doest last very long because the wires get warm again. also i stick a plastic bag over the car then put it in the freezer to stop it geting really wet.
anyway it might be interesting to stick a robot in the freezer or keep it in a cold box before you compete. just an idea.

From Doug

Post Sat Sep 18, 2004 10:18 am 
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Glen
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heh at marayong 5 i was putting my SLAs into jeffs fridge before a fight
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Post Sat Sep 18, 2004 10:47 am 
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andrew



Joined: 16 Jun 2004
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well now u mention it i do hear americans putting their nicads into freezers or fridges to cool them down and get them in good condition for a fight.
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Post Sat Sep 18, 2004 11:33 am 
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Knightrous
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Joined: 15 Jun 2004
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quote:
before i drive my remote control car around i stick it in the freezer for about 1hr. I do this because its makes all the wires cold and lets electrons pass through them much faster and it makes my car go about 5km faster.


The only problem with sticking your car in the freezer is that when you chill it, you make the rubber too cold, giving you a traction loss when you start racing, the plastic in the body becomes more brittle, increasing the chances of part failure when racing and you can even affect the performance of the oil in the shock absorbers, making your standard 20 weight oil become a bit thicker then normal and will give you a stiffer ride during operation.

Personally, sticking my car in the freezer won't help it no more then 5 seconds as the wires will heat straight up when the motor wants it's power.
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Post Sat Sep 18, 2004 11:41 am 
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Windhammer



Joined: 19 Jun 2004
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Location: Roleystone WA


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(you make the rubber too cold, giving you a traction loss when you start racing) :
i take the tyres of before puting them in the freezer. sorry i didnt mention that
(and you can even affect the performance of the oil in the shock absorbers):
i dont have oil shock absorbers.

(sticking my car in the freezer won't help it no more then 5 seconds):
it works for me for about 3-5 minutes.

Post Sat Sep 18, 2004 1:09 pm 
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Spockie-Tech
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Interesting idea, but I cant quite see why it would help. I'm not disputing that it might, just that I cant see why..

Sure, the cooler wires and motor winders will present less resistance to current flow, but as Aaron noted, that will vanish in seconds of running. Wires dont take long to warm up..

And I would have thought that the colder batteries would have far less power available, since they are powered by a chemical reaction and cold slows most chemical reactions.

Thats why car batteries are always rated in "cold cranking amps". The hardest job for a car to start is on a cold morning, with thick cold oil, fuel that doesnt want to vapourise and a battery that is only sluggishly making power. So to deliberately make your batteries cold would seem to be the wrong way to go.

Perhaps however, their is a temperature point above which their resistance starts to increase significantly, limiting the power output more than the slower chemical reactions at the cooler temperature do ? So keeping the battery below that point, but not so cold as to limit the reactions is the ideal temperature ?

Hmm, one would have to do some intensive testing to map the internal resistance and the peak current as functions of temperature and find the crossover point where lack of resistance, but suitable reaction speed is in the sweet spot. anyone looking for a research subject ? Laughing
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Post Sat Sep 18, 2004 9:34 pm 
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Nick
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I recall that Chris Jon mentioned that it was a well known trick to freeze Cordless drill packs to get more out of them. I would guess this is reducing the internal resistance although why it last several minutes is a mystery.

A totally unsupported guess is that itís altering the crystalline structure of the cadmium in the battery - shoot me down in flames if you can...
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Post Sun Sep 19, 2004 1:18 am 
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3Faze



Joined: 26 Jun 2004
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A fair few of the Europeans pack their nicads and overvolted motors with dry ice prior to fights to keep the heat down.

Post Sun Sep 19, 2004 3:23 am 
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Knightrous
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Well charging a battery gets it warm. If you can charge it with out it getting warm and it can soak up that little bit more power with out thermal resistance causing heat up in the cemicals, you might just get that bit more peak and life out of the packs.

I'm gonna absolutely love it when mum finds 4 Drill NiCDs in the freezer and a pair or NiMH's Very Happy
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Post Sun Sep 19, 2004 5:31 pm 
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Maelstrom



Joined: 18 Jun 2004
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Cooling wires only works with superconducting materials and copper is not a superconducting material any reduction in resistance will be negligable at best.
As has been correctly mentioned by Aaron it will take less than a minute for the wires and motor to heat up.
Cooling batteries makes them less effective due to the chemical reaction being slowed down.
The only advantage you will get from cooling batteries is when they are being charged and then it is only protecting them from heat damage, they will take longer to charge and will not gain any more capacity.
As 3faze stated cooling before a fight only prevents heat damage, this will reduce the mount of current you will get from the batteries due to the chemical reaction being slowed down.
Get a battery that is nearly flat (measure it) and place it in a warm place (not the oven or anywhere hot) and you will see a slight increase in output, but only a slight increase.
Nick you are falling prey to an urban myth, I have already stated above why. This is perpetuated by construction workers who have not done any scientific testing, human memory is not exact and recalling the exact time a battery in a drill lasts is unlikely, add to it the fact you are not using the drill exactly the same every time it is used which will affect the time the battery will last. This also applies to your car as you will not drive it exactly the same every time.
Spokie-Tech has fairly well summed it up, you have a very big and extensive research project to find any sweet spot in battery temperature but this comes back to the point Aaron made about the wires, the battery will heat up quickly and there goes any minimal advantage you started with.

If someone mentions a 'trick' to winning then it is just that a 'trick' and is most likely their way of reducing your chances of winning.

Better design of your bot is the only advantge you can get apart form better driving skills.

Post Sun Sep 19, 2004 10:11 pm 
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3Faze



Joined: 26 Jun 2004
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Aaron, your mum needs to understand that the kitchen is full of handy workshop tools:

Dish washer/automotive parts washer
Toaster/Strip heater for plastics
Domestic oven/powder coating oven
Electric carving knife/Reciprocating saw
Hob/Pitch heater for melting ali for casting.
Table/Antweight testing arena
Food mixer/great for twisting wire pairs

Very Happy

Post Mon Sep 20, 2004 3:34 am 
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Valen
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dont forget the stove for sealing the aluminium anodising
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Post Mon Sep 20, 2004 11:46 am 
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Windhammer



Joined: 19 Jun 2004
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Location: Roleystone WA


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Toaster/Strip heater for plastics ?

i think ill try that. Laughing

Post Mon Sep 20, 2004 6:46 pm 
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robo robbo



Joined: 01 Jul 2004
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Location: Perth, Western Australia


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Brett does have a point.
For a chemist's point of view if will slow down the reaction dramitically but the reason people don't notice it is because the batteries and wires will heat up in less then a minute. If you had really high guage wire then it could have anegative effect because the wires wouldn't heat up reducing the flow of electrons.
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Post Mon Sep 20, 2004 9:37 pm 
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JohnMuchow



Joined: 25 Aug 2004
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I'm not sure what effect is being seen with these cooled packs but they can easily be damaged by placing them in a refrigerator or freezer before using them. When cold, localized heating in the cells due to the high amounts of current being drawn from the pack causes distortion of the plate. separator, and other components of the cells. This shortens the life of the pack and gives you no benefits since the pack can't supply more current when cooled that much. In fact, it will supply a lot less current and its capacity will be reduced too.

Some manufacturers do state that high-discharge currents can be drawn at very low temperatures with only a loss of capacity....no mention of damage. But they all also state that for the longest life, use the cells at close to room temperature. Check the data sheets for the cells you're using to be sure.

Now, cooling a pack to a point not too low to cause damage from localized heating, but low enough to prevent the pack from overheating during use might be a good idea. No way to determine the proper temperature unless a LOT of testing is done though....wayyyyyy too many variables here IMHO.
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Post Tue Sep 21, 2004 6:38 pm 
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