# Recharge With Hand Crank



## ssw422 (Feb 3, 2011)

Hi, 
I want to find the best way to store energy from a hand crank, something like this http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=53272&Detail=1 
I was thinking of a supercapacitor because I need to charge a vehicle and it has to move autonomous all within a 10 minute period.
Any suggestions will be greatly appreciated!

EDIT: its for an EV the size of a child's toy (or smaller), also Its a competition so we have in total 10 minutes to 1) charge the vehicle(no energy in the vehicle at start) And 2) Let it move autonomously in the remaining time


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## major (Apr 4, 2008)

ssw422 said:


> Hi,
> I want to find the best way to store energy from a hand crank, something like this http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=53272&Detail=1
> I was thinking of a supercapacitor because I need to charge a vehicle and it has to move autonomous all within a 10 minute period.
> Any suggestions will be greatly appreciated!


Hi ssw,

I suggest you read this thread. http://www.diyelectriccar.com/forums/showthread.php?t=49583&highlight=mining This should explain what to expect from generation by hand, or foot as it were.

Capacitor or battery, either way, you have to crank a lot to get enough stored to move a vehicle of any size very far or for very long.

Regards,

major


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## Sunking (Aug 10, 2009)

ssw422 said:


> I was thinking of a supercapacitor because I need to charge a vehicle and it has to move autonomous all within a 10 minute period.


At first I thought this was a joke, but after thinking about it I can see you are serious. 

OK that hand crank generator maximum output is 25 watts. So with 10 minutes full output = 25 watts x .1666 hours = 4.16 watt hours.

So what size vehicle are we talking about here? Unless we are talking a child's toy car, you are not going to go anywhere with 4 watt hours. Crank it for 24 hours you get 600 wh about enough to go a mile or two.


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## ssw422 (Feb 3, 2011)

Yes, I forgot to mention its for an EV the size of a child's toy (or smaller). I was wondering what capacitance and circuit that I should look up.
Thanks for the replies!


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## major (Apr 4, 2008)

ssw422 said:


> Yes, I forgot to mention its for an EV the size of a child's toy (or smaller). I was wondering what capacitance and circuit that I should look up.
> Thanks for the replies!


You're welcome. And you just have to do the math. Figure how much energy you need and then use E= ½CV². Figure at least 25% more, maybe twice the energy in the caps because it is very difficult to use all the energy as cap voltage approaches zero. A reason you may want to consider batteries.

major


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## Sunking (Aug 10, 2009)

Charge efficiency of caps is not good.


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## major (Apr 4, 2008)

Sunking said:


> Charge efficiency of caps is not good.


98-99% is not good  Charge efficiency (and discharge efficiency) of capacitors is excellent due to the low ESR. Much better than batteries, even Lithium. That is the one outstanding attribute of capacitors. Of course it depends on the load, type of cap, etc, but in general, efficiency is great.


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## dtbaker (Jan 5, 2008)

ssw422 said:


> Hi,
> I want to find the best way to store energy from a hand crank, something like this http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=53272&Detail=1
> I was thinking of a supercapacitor because I need to charge a vehicle and it has to move autonomous all within a 10 minute period.
> Any suggestions will be greatly appreciated!


you need to re-think.

a human on a very efficient bike (using very strong legs) can output a steady 250watts for an hour if they are very fit, with sprints up to maybe 800+ watts for 30 seconds if they are great. a hand crank will be WAY less than that.

most average people will struggle to output above 100-150 watts for an hour.

the typical EV takes 200 whr to move it a mile.

do the math.


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## icec0o1 (Sep 3, 2009)

I would suggest staying away from capacitors. Just do the math on how much energy you can crank out for the required amount of time (9 minutes?) and store that into the appropriately sized lipo battery. Supercaps aren't good for energy density and are usually used for very high current storage/dissapation. Hand cranking isn't going to give you high current.


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## ssw422 (Feb 3, 2011)

So i should look at lithium batteries? In less then 10 minutes, i need to charge it quickly using only manpower


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## Ziggythewiz (May 16, 2010)

What is the contest? Furthest movement in 10 min? Fastest?

If you're only limited to human power, and have the resources, do a bike generator. You can sustain 10X the power you could with hand crank.

if you can do 200 watts (quite doable for 10 min) that's 33 watt hours, enough to mathmatically (who knows the practicality) move an actual EV over 1/10th of a mile.

A toy car should be able to drive out of sight.

Another idea would be to crank a slingshot for 10 min...then let it fly.

or use a trebuchet...are those against the rules?


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## dtbaker (Jan 5, 2008)

ssw422 said:


> So i should look at lithium batteries? In less then 10 minutes, i need to charge it quickly using only manpower



type of battery is not relevant. what is relevant is that 'man-power' is limited to maybe 300 watts for a ten minute sprint for a GOOD cyclist.... yielding a max around 50 wHr, which might move a small car about 1/4 mile on the level.

thats using both legs at a gut-busting 10 minute sprint... not a one-hand crank.

... I just re-read though, and since you are not trying to move a real car, the plan changes...

capacitors tend to be big, heavy, and expensive compared to batteries, BUT have the advantage of quick charge and quick discharge without damage. You could also go for a sprint or flywheel, but have issues regulating the start and power output of a purely mechanical system.

Part of your decision is going to be how 'empty' does your power supply have to be and how do you prove you are not starting with a pre-charged battery? Or, how about a guy on a bike with NO motor; could go close to 3 miles!


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## icec0o1 (Sep 3, 2009)

dtbaker said:


> type of battery is not relevant. what is relevant is that 'man-power' is limited to maybe 300 watts for a ten minute sprint for a GOOD cyclist.... yielding a max around 50 wHr, which might move a small car about 1/4 mile on the level.
> 
> thats using both legs at a gut-busting 10 minute sprint... not a one-hand crank.


Type of battery is relevant... I wouldn't want to charge a lead-acid battery with a hand crank. And 50wHrs would be enough for 2 miles for an electric bycicle. I think it'd be enough for at least a mile for a toy car traveling less then 10mph where you're only fighting friction and not air density.


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## GerhardRP (Nov 17, 2009)

Do you have a link to the rules of this contest?
Get a wheelchair marathoner to crank for you.
Gerhard



ssw422 said:


> Hi,
> I want to find the best way to store energy from a hand crank, something like this http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=53272&Detail=1
> I was thinking of a supercapacitor because I need to charge a vehicle and it has to move autonomous all within a 10 minute period.
> Any suggestions will be greatly appreciated!
> ...


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## ssw422 (Feb 3, 2011)

The device has to be completely empty of energy at the start of the competition. The time start when we recharge the vehicle (only man power is allowed). We must leave the device we used to charge the vehicle on the vehicle. 
The whole point of the competition is to build a vehicle that will recharge and go as many times back and forth (about 40 inch forward and 40 back) under 10 minutes.


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## ssw422 (Feb 3, 2011)

GerhardRP said:


> Do you have a link to the rules of this contest?
> Get a wheelchair marathoner to crank for you.
> Gerhard


PM was SENT


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## frodus (Apr 12, 2008)

Why not use air and a tank.


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## Duncan (Dec 8, 2008)

Why not use an elastic band?

Its not as silly as it sounds an elastic band or spring system would give you your motor and generator in one piece


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## icec0o1 (Sep 3, 2009)

I would definately go with lipo. Find a battery that's at least 6C charge so you can get all of the energy in in 10 minutes. Try to find a hand crank that has like 100 watt max output or something like that. And most important, if you're going back and forth only 40 inches, make it as light as humanly possible because innertia is your enemy.

Depending on your mechanical/electrical abilities, I'd probably use only one motor and have a high gearing system that also works as a hand crank. Like put a hole in one of the wheels (if they're made of plastic) and screw on a handle to charge it up. If you only use one motor, it'll save on weight and it'll be far more powerful than the 25W hand generator in your link.


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## Tesseract (Sep 27, 2008)

ssw422 - if you had only provided the details a little sooner I, at least, wouldn't have dismissed your post as from yet another... ahem... crank.

Sounds like a cool little contest, and an excellent engineering exercise.

Duncan - a spiral wound spring is reasonably efficient but rubber/elastic bands are less so. I don't recall the efficiency off the top of my head, but I do know that a fair amount of the kinetic energy put into an elastic band is converted into heat as it is tensioned. Batteries/capacitors might just be superior in this regard.

icec0o1 - I think you've got the right idea, but given the distance to be traveled and the requirement that the vehicle start with zero energy stored, capacitors would be a much better choice of storage medium 

Anyway, ssw422, a shunt wound motor might be the best choice of motor/generator here. Personally I'd like to see a bidirectional buck/boost converter in between the motor/generator and capacitor bank but that might be best reserved for if you are the returning champions next year and facing stiffer competition 

Not going to work out all the relevant equations, but being familiar with the capacitor energy storage equation will serve you well: the energy stored in a capacitor in watt-seconds (Joules) is 0.5CV²


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## major (Apr 4, 2008)

ssw422 said:


> go as many times back and forth (about 40 inch forward and 40 back) under 10 minutes.


Sort of sounds like a good job for a pendulum, back and forth. Perhaps a machine where you store energy by lifting a weight and let it lower itself thru back and forth movements like a pendulum. Could you have a wheel with a 40 inch circumference so one revolution would cover your distance?

O.K. Weird and not EV related. But just one of those brain teasers


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## icec0o1 (Sep 3, 2009)

major said:


> Sort of sounds like a good job for a pendulum, back and forth. Perhaps a machine where you store energy by lifting a weight and let it lower itself thru back and forth movements like a pendulum. Could you have a wheel with a 40 inch circumference so one revolution would cover your distance?
> 
> O.K. Weird and not EV related. But just one of those brain teasers


Sound interesting but I figure getting as much energy into the car in like 9 minutes and letting it run for a minute is what he should be aiming for. How much weight can you lift in 9 minutes? A thousand pounds? Poor little toy car  

Actually I guess for 40 inches back and forth would be very time demanding... might have to be 5 minutes cranking and letting it run for 5 minutes. 

I want to participate in your competition.... my school never had fun things like this


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## icec0o1 (Sep 3, 2009)

Tesseract said:


> icec0o1 - I think you've got the right idea, but given the distance to be traveled and the requirement that the vehicle start with zero energy stored, capacitors would be a much better choice of storage medium


Can you expand on this Tesseract? What kind of advantages would a capacitor bank have over a 4s1p lipo that has a 5C charge current, can hold 26.64 watt hours = 8 minutes of charging at 200 watts, weighs only 222 grams and costs $15 bucks? If that's not enough, a better one at 10C charge current (can be charged to full in 6 minutes), holds 32.56 watt hours, weighs 257g and costs $31 bucks? 

When weight is a pretty big factor, I figure lipo's the way to go. I'm not that knowledgeble with caps so I'm curious for your insight. Btw, I'll post a link to the batteries...

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9938
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=11952


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## Tesseract (Sep 27, 2008)

icec0o1 said:


> ...What kind of advantages would a capacitor bank have over a 4s1p lipo...


No special insight applied here, I just picked up on this one rule for the contest that pretty much eliminates batteries from use:



ssw422 said:


> The device has to be completely empty of energy at the start of the competition....


So don't need to be a fancy-pants engineer to work out this problem...


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## major (Apr 4, 2008)

Tesseract said:


> No special insight applied here, I just picked up on this one rule for the contest that pretty much eliminates batteries from use:
> 
> 
> ssw422 said:
> ...


I don't wear fancy pants, but you could use a NiCad  No problem there with being "empty".

Probably the lightest "container" for storing energy would be a balloon.


ssw422 said:


> We must leave the device we used to charge the vehicle on the vehicle.


 But then do you need to leave your lungs aboard? Where do you separate the power source from the energy storage charging device 

maj


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## DIYguy (Sep 18, 2008)

Just high level here..... and perhaps I should read all the rules.... but it just seams that for the requirement to move back and forth, short time frame and energy demands.... you may want to think about something other than electrical especially not batteries. Some of the ideas like energy stored in springs or perhaps air pressure, or maybe even elastic is not so crazy for such an application. The efficiency of elastic compared to springs is pretty much a mute point I think..when comparing the energy needed to accelerate, stop and accelerate again something as many times as possible back and forth in a short time. The torsional springs used in wind up cuckoo clocks maybe the answer. I have a small wall hanging one that has two keys...one for clock works and one for gong. I wind it up once per month. Having a place you could wind up with a key...like maybe on the axle hub even and of course a ratchet catch to hold it. Do you get to "charge" or wind up more than once in the 10 minutes? 

Cheers,
Gary
PS maybe something like this on a smaller scale.....? http://www.dhambachari.com/2010/09/mechanical-regenerative-braking-system.html


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## icec0o1 (Sep 3, 2009)

> _The device has to be completely empty of energy at the start of the competition...._





Tesseract said:


> No special insight applied here, I just picked up on this one rule for the contest that pretty much eliminates batteries from use:
> 
> 
> 
> So don't need to be a fancy-pants engineer to work out this problem...


Empty can have many meanings. A capacitor has some energy as well unless you cool it down to absolute 0 kelvin. A lipo battery is "empty" when it's at 2.9 volts.


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## icec0o1 (Sep 3, 2009)

DIYguy said:


> Just high level here..... and perhaps I should read all the rules.... but it just seams that for the requirement to move back and forth, short time frame and energy demands.... you may want to think about something other than electrical especially not batteries. Some of the ideas like energy stored in springs or perhaps air pressure, or maybe even elastic is not so crazy for such an application. The efficiency of elastic compared to springs is pretty much a mute point I think..when comparing the energy needed to accelerate, stop and accelerate again something as many times as possible back and forth in a short time. The torsional springs used in wind up cuckoo clocks maybe the answer. I have a small wall hanging one that has two keys...one for clock works and one for gong. I wind it up once per month. Having a place you could wind up with a key...like maybe on the axle hub even and of course a ratchet catch to hold it. Do you get to "charge" or wind up more than once in the 10 minutes?
> 
> Cheers,
> Gary
> PS maybe something like this on a smaller scale.....? http://www.dhambachari.com/2010/09/mechanical-regenerative-braking-system.html


I don't know about you but I can't imagine how big a spring or a rubber band would have to be to hold the energy of 8 minutes of arm cranking. I feel like unless it's made of titanium or something, it'll just shatter and explode.


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## Tesseract (Sep 27, 2008)

major said:


> I don't wear fancy pants, but you could use a NiCad  No problem there with being "empty".
> 
> maj


Hmmmm... yeah, that's true for Ni-Cd, and also for Nickel-Iron (Edison) cells. However, Ni-Cd has terribly Coulometric efficiency... something like 65-70%, IIRC, and though I have no idea what it is for Edison cells, I'm guessing it's not too great for them either. 

I'm not even gonna touch that lungs question... 



icec0o1 said:


> Empty can have many meanings. A capacitor has some energy as well unless you cool it down to absolute 0 kelvin. A lipo battery is "empty" when it's at 2.9 volts.


Okay, if you want to be pedantic about it then _everything_ has "energy" unless it is at absolute zero, and even then E=mc² still applies so, umm... no dice there.

And you can keep pulling electrons from a LiPo cell all the way to 0V, and even then as soon as you remove the load the voltage will almost certainly spring back up a bit. Regardless, you're going to get a big surprise the next time you try to recharge it starting from 0V... the kind of surprise that needs a bucket of sand to smother.


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## icec0o1 (Sep 3, 2009)

Tesseract said:


> Okay, if you want to be pedantic about it then _everything_ has "energy" unless it is at absolute zero, and even then E=mc² still applies so, umm... no dice there.
> 
> And you can keep pulling electrons from a LiPo cell all the way to 0V, and even then as soon as you remove the load the voltage will almost certainly spring back up a bit. Regardless, you're going to get a big surprise the next time you try to recharge it starting from 0V... the kind of surprise that needs a bucket of sand to smother.


I'm saying it's fairly reasonable to assume that he could explain to his professor that he has a low voltage cut-off at 2.9v. He can flip the switch and show that the car won't move. Then crank it up and let it run untill the LVC shuts it off. 

The challenge would indeed be pedantic if it won't allow such examples.


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## DIYguy (Sep 18, 2008)

icec0o1 said:


> I don't know about you but I can't imagine how big a spring or a rubber band would have to be to hold the energy of 8 minutes of arm cranking. I feel like unless it's made of titanium or something, it'll just shatter and explode.


Maybe there are some ways. First there are some thin ones that can be wound many times. Also, you could mount several in series perwheel. Also, you have 4 wheels ( I think lol). 
Titanium is not a material for springs. They are made from carbon steel, hardened and then tempered to resist breaking. They usually do eventually break from fatigue. 

This type can be wound many times. http://2.imimg.com/data2/HV/CQ/IMFCP-2395955/clock-spring-constant-force-500x500.jpg

It still could be an issue depending on design skills of the "doer" so... you may have a point. That's why I was wondering if you were allowed to "charge" or wind, more than once in the 10 min.


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## icec0o1 (Sep 3, 2009)

DIYguy said:


> Maybe there are some ways. First there are some thin ones that can be wound many times. Also, you could mount several in series perwheel. Also, you have 4 wheels ( I think lol).
> Titanium is not a material for springs. They are made from carbon steel, hardened and then tempered to resist breaking. They usually do eventually break from fatigue.
> 
> This type can be wound many times. http://2.imimg.com/data2/HV/CQ/IMFCP-2395955/clock-spring-constant-force-500x500.jpg
> ...


32 watt hour battery can provide 1 hp for 2.6 minutes. Do you really think a clock spring can come even close? You would need a spring the size of a grandfather clock. I just don't see it, but with that I'll leave it be.


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## DIYguy (Sep 18, 2008)

icec0o1 said:


> 32 watt hour battery can provide 1 hp for 2.6 minutes. Do you really think a clock spring can come even close? You would need a spring the size of a grandfather clock. I just don't see it, but with that I'll leave it be.




I'm assuming this is some kind of little kiddie car/toy. Also, a "clock spring" is a generic term for a circular wound torsion spring. It could be large or small, many turns or few.

BTW, thanks for the lesson on batteries .


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## Tesseract (Sep 27, 2008)

icec0o1 said:


> I'm saying it's fairly reasonable to assume that he could explain to his professor that he has a low voltage cut-off at 2.9v. He can flip the switch and show that the car won't move. Then crank it up and let it run untill the LVC shuts it off.
> 
> The challenge would indeed be pedantic if it won't allow such examples.


You do have a point, but there's just one problem... the LVC circuit itself requires power to operate. That said, there are some clever workarounds involving latching relays - not something I'd trust in an actual commercial device, but certainly acceptable for a one-off like a contest entry.


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## Duncan (Dec 8, 2008)

Back when I was a lad - a while ago!
there were flying model competitions with rubber powered (not RC) models

These things would take off nearly vertically and have to stay in the air for 25 minutes

The elastic would be a carefully made string of selected elastic strips - for a 2 ft long fuselage the initial elastic would be about 4 ft long and would be wound down to its final installation with a hand cranked drill -

http://www.youtube.com/watch?v=Ec9XqhQFxqo

For a plane the load the elastic "motor" put on the fuselage was a problem

For a car that has to go back and forth a long fuselage would probably not be problem

in the open class models sometimes had an elastic motor that was half of the weight of the plane

Power?

The Wakefield class in the video would compete with IC engined planes - the IC engine would produce ~ 0.5 hp for 5 seconds or about 0.5 watt hours
The rubber motor in this class is 30gm

30gm for 0.5 whr , = 16 whr/kg
TS 100Ah = 320 whr - 3,500gm - = 91 whrs/Kg

BUT the rubber motor is the motor and generator as well as the battery!

http://en.wikipedia.org/wiki/Free_flight_(model_aircraft)


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## frodus (Apr 12, 2008)

isn't this a COMPETITION? as in, you're supposed to come up with the solution yourself? The calculations of the cap size for the energy needed are readily available on the internet (and in this thread). All of the answers you seek are there if you spend some time (not much time BTW) doing some work on your own.

I just don't see it as much of a competition if people here are doing the work for you. I mean, are you actually figuring anything out on your own, or just getting other people to do the work for you and tell you how to do it?

Sounds a lot like cheating to me.


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## ssw422 (Feb 3, 2011)

I work out a couple things... Asking for a second opinion isn't cheating.


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## frodus (Apr 12, 2008)

Oh, this sounds a lot like you were looking for answers..... Not really a second opinion if you're looking for someone elses opinion initially....



ssw422 said:


> I was wondering what capacitance and circuit that I should look up.
> Thanks for the replies!



And in all of your posts, none of them show that you've done anything at all, just asked lots of questions on what you need and if your idea would work.....

doesn't apear that you've actually done any calculations.... but if you have, feel free to share, that way we could offer suggestions based on the work you've already done.


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## icec0o1 (Sep 3, 2009)

frodus said:


> isn't this a COMPETITION? as in, you're supposed to come up with the solution yourself? The calculations of the cap size for the energy needed are readily available on the internet (and in this thread). All of the answers you seek are there if you spend some time (not much time BTW) doing some work on your own.
> 
> I just don't see it as much of a competition if people here are doing the work for you. I mean, are you actually figuring anything out on your own, or just getting other people to do the work for you and tell you how to do it?
> 
> Sounds a lot like cheating to me.


Like you've never cheated on a test before  

He probably doesn't have the time to analyze every possibility and can use the help to narrow down his overall design. In these competitions, the small things are more important anyways. Whether he uses caps or lipos is kind of irrelevant if he is still going to use a 25w hand crank generator when he can make at least a 100w one quite easilly.


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## frodus (Apr 12, 2008)

icec0o1 said:


> Like you've never cheated on a test before


Nope. Didn't have to. 



icec0o1 said:


> He probably doesn't have the time to analyze every possibility and can use the help to narrow down his overall design. In these competitions, the small things are more important anyways. Whether he uses caps or lipos is kind of irrelevant if he is still going to use a 25w hand crank generator when he can make at least a 100w one quite easilly.


Sorry, but when I went to school and they gave us these challenges, forums and wikipedia didn't exist and we were required to do our own homework. They'd give us a team and a week to solve the problem. Thats part of the engineering curriculum in my school. They taught you to actually engineer something.

Asking for the answer does nothing to teach you how to design a system. 


He just doesn't apear to be doing much design himself.


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## icec0o1 (Sep 3, 2009)

Eh, I just don't see the need to reinvent the wheel. And heck, we're supposedly quite knowledgeable in the field and we can't agree on the best design ourselves. But you're right, after he settles on a design (caps + hand crank generator) I would've only helped him by linking to relevant information


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## frodus (Apr 12, 2008)

Now, about what he's stated so far (about caps and a generator), it sounds like a "sound" idea. 

But he'll have to calculate the amount of energy needed to move a XXlb vehicle back and forth, how much it'l weigh, how many times he wants to go back and forth and what energy needs to be stored in the caps. He'll have to account for frictional and electrical losses. Then he can calculate what voltage and capacity he'll need for the capacitors. He can size a generator once he gets an idea of how much energy needs to be stored. The design requirement is not revolving around the generator, its the mechanical/electrical output of the vehicle.


It's a process and he'll have to do it more than once, since the number of capacitors might change the weight and effect the losses which can effect the energy needed which effects the number of capacitors..... rinse and repeat.


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## icec0o1 (Sep 3, 2009)

frodus said:


> Now, about what he's stated so far (about caps and a generator), it sounds like a "sound" idea.
> 
> But he'll have to calculate the amount of energy needed to move a XXlb vehicle back and forth, how much it'l weigh, how many times he wants to go back and forth and what energy needs to be stored in the caps. He'll have to account for frictional and electrical losses. Then he can calculate what voltage and capacity he'll need for the capacitors. He can size a generator once he gets an idea of how much energy needs to be stored. The design requirement is not revolving around the generator, its the mechanical/electrical output of the vehicle.
> 
> ...


 
It's funny... I would go about it the exact opposite way. I'd start with the biggest + lightest generator I could build/power without getting a heart attack for about 7-8 minutes (150 watts+?), find the size of the caps/batteries that it would require to store all of that energy, and then build the lightest possible car that could put out all of that energy down in 2-3 minutes. Then test it a bunch of times and see what optimal ratio of cranking to running time would gives the best results.


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## frodus (Apr 12, 2008)

Well, the end result, the solution required, is the actual movement of the vehicle, not charging it.

Whether you start calculations at the wheels or at the generator, the end result required is the same. You're just going at it from the generator side. You can use a 25W generator, or someone pedaling a bike to spin an alternator. But starting from what is actually required at the wheels and working your way back, tells you what you actually need, rather than using an arbitrary starting point by chosing a huge generator. you may not even need it, or be able to use it, and may be overdesigning on the generator side.

Look at constraints like number of times it MUST go back and forth, limits on voltage, limits on current, limits on cost, limits on weight, limits on how much energy can be put into the system (1 person versus 2 people), etc.

When there are so many variables, you really do need to sit down and choose which one you are "fixing". In this case, I recommended to keep the end result fixed and calculate back.



Its my same methodology in helping people design their vehicles. Some people just want to throw a bunch of batteries/motors/controllers in a vehicle to get a fast/powerful end result, but they never do the calculations to see what they actually need to get the results they want...... Sometimes they fail because they don't look at the end result needed and don't design the system based on those constraints.

You don't design an EV around a charger do you? you size the charger according to the specs of the pack.

Your way will probably net the same result, but you'll be designing around a variable output that may not meet the requirements of the competition. The entire project is about finding the variables, finding the constants and defining the constraints.


Get an efficient motor and controller that will work across the WHOLE discharge curve of the capacitors (they're linear, and as voltage drops, the controller must work along the entire curve). Also, as voltage drops, the current needed to output the same power increases, compounding the problem.


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## icec0o1 (Sep 3, 2009)

frodus said:


> You don't design an EV around a charger do you?


I would if it was intended to go as far as possible in 10 minutes (charge + motion).


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