Go to Post Maybe Dave's just bananas for FVC? - Billfred [more]
Home
Go Back   Chief Delphi > Technical > Electrical
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Closed Thread
 
Thread Tools Rate Thread Display Modes
  #1   Spotlight this post!  
Unread 21-02-2007, 23:15
Ronald_raygun Ronald_raygun is offline
Team Finance/Engineering
AKA: Jose Cabanero
FRC #0019 (BigRedRobotics)
Team Role: Leadership
 
Join Date: Jan 2005
Rookie Year: 2005
Location: Conneticut
Posts: 80
Ronald_raygun is a jewel in the roughRonald_raygun is a jewel in the roughRonald_raygun is a jewel in the rough
Send a message via AIM to Ronald_raygun
Re: Capacitor Question

Al,

I can't thank you enough for your effort in providing me the help I need to get this project off the ground. I know I can't say this enough, but thank you for your response.

As for the motor, presumably dumping twice the voltage into the motor would also have the motor draw twice the amps, which is where I get the "4 times the horsepower figure" "When you double the voltage, you also double the amperage that a motor can draw. This means that the power that can be produced goes up by a factor of four."

I still don't quite understand the charge/discharge characteristics of a general capacitor (supercap or otherwise).

Do I need to charge it at the rated voltage? (i.e. 1v source into a 2v cap)
Can I discharge it at a different voltage? (i.e. 50V cap into a 6v motor, or 2v cap into a 6v motor)

As for other forms of energy on the car...As long as its powered by the fuel cell, it's generally allowed, within reason (No fusion/fission reactors, rubber bands, etc.) As for flywheels, they are definitely easier to implement for me, but engaging them to the drive wheel doesn't seem too feasible given the size and power limitations. (Weight as you remember is unlimited)

All this circuit talk has my head spinning. The 555 Timer circuit I know is pretty common, but I have no idea how it works. Is there some sort of simulator or circuit-building program that you recommend? That might make things easier.

I just need to design a circuit to incorporate a capacitor into my design so that I get a boost at the start of a run.n
__________________
Team 19...Big Red
  #2   Spotlight this post!  
Unread 22-02-2007, 08:06
Unsung FIRST Hero
Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1996
Location: Wheeling, IL
Posts: 10,798
Al Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond repute
Re: Capacitor Question

Jose,
You can charge a capacitor to any voltage. It only becomes a problem when you are trying to charge it to a voltage that is higher than it's rating. You can use the 1 volt fuel cell to power a voltage multiplier much like the article in your post above. Maxim has a few handy ICs that are designed for these applications. If your motor is rated for 6 volts then charge a cap up to 6 volts and then dump it into the motor. 6 volt capacitors are generally smaller in size than a 16 or 25 volt cap but you can still use the higher rated cap charged to 6 volts.
Capacitors are funny little beasts. When charging, the voltage starts out very small and rises exponentially until max charge is reached. This takes about 6 time constants to achieve, where t=R*C. The voltage that appears at the terminals will be V(cap) =Vin(1 - e^{-t/RC}) if you are solving for time. The charge current is the inverse of this. Current is maximum at the start of charge and falls off to zero when a cap is fully charged. In discharge both current and voltage are reversed. The cap will deliver max voltage and current at the start of discharge both falling to zero at the end of discharge, again as an exponential function. this link has a good curve and explanation http://hyperphysics.phy-astr.gsu.edu...ic/capchg.html
The 555 timer is a special circuit that uses the function of RC timing (cap charge/discharge) to perform timing functions. If you were to use the same cap for both motor function and timing, that would be pretty cool.
Once you take a look at the charge discharge curves, you will start to get a feel for the action of the cap in your application. During charge you can have one time constant that is determined by the charging circuit series resistance and chosen so that you do not exceed the fuel cell 500 ma max current. On the discharge side, your time constant is now determined by the series resistance of the motor and wires. The discharge constant will be very short due to the low series resistance of the motor. Say you were using a motor like the Fisher-Price motor. It has a resistance of about 0.12 ohms. With a bank of caps rated at 0.5 farad the bank would be fully discharged in 6 time constants or 6*0.5*0.12=.36 seconds. But it would only produce some useful current for perhaps 1 or 2 time constants. Remember that the using the equation above, one time constant will discharge the cap to 37% of it's fully charged value. So in 0.06 seconds the voltage in the cap will be down to 2.2 volts but the current will be as high as 50 amps. With all things considered, you might find that in 0.06 seconds, you may have not been able to transfer enough current to get the motor turning. Only experimentation will tell, different motors will have different resistance and power curves. Good luck.
As to the flywheel, all you have to do is have a pulley attached to your drive wheels that pivots against the flywheel. When the race starts, just allow the pulley to fall against the flywheel to conduct the flywheel energy to the drive wheels. A spring would help do that as well as having a grippy surface on the pulley. Then use the fuel cell to drive a motor that spins up the flywheel.
__________________
Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
________________________
Storming the Tower since 1996.

Last edited by Al Skierkiewicz : 22-02-2007 at 08:10.
Closed Thread


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Servo behavior question / advanced servo/PIC programming question DanL Electrical 12 18-10-2005 18:33
pic: 610 Flux Capacitor (after teaser 2) The_Goodie Robot Showcase 10 04-02-2005 22:23


All times are GMT -5. The time now is 20:42.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi