Electric Vehicle C

Post Reply
User avatar
sean9keenan
Member
Member
Posts: 107
Joined: May 10th, 2007, 3:31 pm
Division: Grad
State: PA
Location: Caltech
Has thanked: 0
Been thanked: 0

Re: Electric Vehicle C 2009

Post by sean9keenan » November 6th, 2008, 8:58 am

  1. No, at least not besides the Time score (out of 50)
  2. No, because the voltage is the same
  3. Not sure, many different braking systems are available, and personally I don't see much difference in the braking systems (esp considering the speed and likelyhood of the car swerving out of control (as is the issue more so with bikes))
  4. No, although it might factor into your braking
  5. Not sure... just keep in mind that you want need to stay on the center line which is easier with a wider wheel base, plus you need the car to go straight. My opinion -> bigger == better
Hope that helps, Good luck

-Sean Keenan
SoCal Event Supervisor. H2S2O for ever. Competed in Builds & Physics events

User avatar
sirup96
Member
Member
Posts: 6
Joined: November 4th, 2008, 7:52 am
Division: C
State: WI
Location: WI Menomonie
Has thanked: 0
Been thanked: 0

Electric Vehicle C 2009

Post by sirup96 » November 6th, 2008, 2:16 pm

Now I know this team last year had battery problems last year :? . They use rechargeable and I'm thinking of doing the same. Are there still size D rechargeable batteries? And would it be better if put a 5v regulator in line with the batteries to the microcontroller so there always a consistent voltage? Are there any problems with a regulator?

O and I like to hear 50 free swimming times mine is "29.38" ya! :D
Sirup96
"Take them out back"
Love to Swim.
Fixing others problems.
Have to carry random parts everywhere. Anyone need a gulf ball, flat head and a 30 dead C battery?

User avatar
sean9keenan
Member
Member
Posts: 107
Joined: May 10th, 2007, 3:31 pm
Division: Grad
State: PA
Location: Caltech
Has thanked: 0
Been thanked: 0

Re: Electric Vehicle C 2009

Post by sean9keenan » November 7th, 2008, 3:44 pm

You can use rechargeable batteries in fact most rechargeable batteries actually operate at slightly less than 1.5 V, at 1.3 V. Regardless they do sell D rechargeable, along with C's AA's and AAA's, they all have the same voltage, but last different amounts of time pretty much (a rating called a milliamp-hour (a backwards way of saying energy)). When buying the batteries make sure that you aren't buying a AA battery that has been wrapped up in a D sized battery because that is of no use and sometimes they do that when they think what you really wanted was just a battery that fits where D batteries fit. :-/. Basically compare the Milliamp hours on the batteries before you buy one...

As to the V regulator, you will probably need one if you plan on using a micro controller, since they generally freak out when they don't have 5 V, more than likely if you haven't been regulating your supply voltage then the micro controller (and I assume accompanying components) has a build in 5V regulator. You could check this by measuring the potential across the actual IC and seeing if it's 5 V across the two power pins. While it is true that regulators do have line fluctuation (error) they often are better than just attaching something without a regulator. Plus even if your circuit has a regulator inside of it there is really no reason to try it to hard as it may just get burned out if it isn't meant to handle that much power. (Power is equal to (Vin-5V) * Current). If it gets to hot then you'll have a tougher time replacing it than if you just had two in a row... The only reason I might see for not attaching the V regulator is if it's draining to much power from the circuit. Something else to note is that if there is an internal V regulator in your micro controller the voltage input might need to be significantly higher than 5 V based on the construction of the regulator in which case I would not recommend using a V reg on the outside as it might result in supplying less than 5 V to your microcontroller, which would be bad

Wow, that was a really long rant about nothing, just make lots of measurements and keep the V across the IC 5V...

btw, what was that about 50 free swimming times mine is 29.38?
SoCal Event Supervisor. H2S2O for ever. Competed in Builds & Physics events

andrewwski
Admin Emeritus
Admin Emeritus
Posts: 954
Joined: January 12th, 2007, 7:36 pm
Division: Grad
Has thanked: 0
Been thanked: 11 times

Re: Electric Vehicle C 2009

Post by andrewwski » November 7th, 2008, 4:57 pm

You're going to have a tough time finding a 5V regulator that is stable with an input voltage of only 6V.

gh
Admin Emeritus
Admin Emeritus
Posts: 323
Joined: October 22nd, 2003, 5:47 pm
Division: Grad
State: NY
Location: CA
Has thanked: 0
Been thanked: 0
Contact:

Re: Electric Vehicle C 2009

Post by gh » November 7th, 2008, 5:43 pm

The problem is that you don't have 6V. Only alkaline (non-rechargeable) cells are 1.5V each. NiCd/NiMH cells come in the same form factors, but they are nominally 1.2V per cell. Their charge voltage (voltage that they are charged up to) is about 1.5V, but they only maintain that voltage within the very beginning of their discharge curve. See the following diagram:
Image
In addition, the voltage regulator will need a certain amount of breathing room between the voltage it takes in an the voltage it regulates to, called the "dropout voltage." There are "low-dropout" regulators that can handle drops of less than 0.5V, so your input can be as low as 5.5V. Once again, this doesn't fix much because your rechargeables only provide 1.2×4=4.8V reliably.

Possible solutions:
  • Use electronics that are rated for operation at 3.3V, which is about as common as 5V electronics are. You'd be using a 3.3V voltage regulator to go from ~4.8V to 3.3V.
  • Use a boost DC-DC converter that can convert a lower voltage to a higher voltage. You'd raise the voltage from ~4.8V to some arbitrary voltage (9V or 12V?), and use a 5V regulator to step it back down.
  • Use fresh alkaline batteries every time you make a run (including practice runs). You'd step it down from ~6V to 5V for your electronics. This sounds really impractical.
“Rather fail with honor than succeed by fraud.” —Sophocles
If you are looking to give help or get help:
[wiki][/wiki] > Forum post > > PM > Email
Don't forget the Image Gallery, the , and the list of Exalted User medals.

captbilly
Member
Member
Posts: 94
Joined: April 17th, 2005, 11:06 am
Has thanked: 0
Been thanked: 0

Re: Newbie

Post by captbilly » November 7th, 2008, 10:07 pm

nctarheel wrote:I am very new to the Electric Vehicle, as it was kind of thrust upon me this year by the club adviser. There are a few questions that I have about this event that I was not able to find answers to at the North Carolina and US Science Olympiad web pages:
1) Are you judged any at all on how fast your vehicle travels the assigned distance?
2) Would I be penalized for using 4 D Cell batteries?
3) What is a good way to brake the vehicle in a straight line? I was thinking a front-drive, rear brake system would be more stable, kind of like on bicycles (without the front-drive).
4) Is weight factored into the score?
5) Which of these combinations would work best?
-Low-riding body
-High-riding body
-Slender-width body
-Wide-width body
-Long-length body
-Short-length body
-Wide axle/tire track

1. At regional and state competition you only have to ensure that the travel time is within the acceptable limits, less than 45 seconds. Of course you have to be able to predict the travel time accurately since that is 1/4 of the total possible point. At National competition you must adjust the speed to match what the event coordinator specifies.
2 As long as their voltage is labeled as 1.5 volts or less, you can use up to 4 batteries of any type you choose
3. As long as you don't lock up the wheels during breaking it makes little difference which wheels you use. If you are going to use the old screw and wingnut break then it should go on the front. It may seem a bit unintuitive but locking the front wheels on a vehicle (car for example) is less likely to cause an instability.
4. Weight is not factored in any way.
5. The rules this year make allow little choice of length and width. WHeelbase must be within a narrow range. Maximum track (measured to the outside of the wheels) is in the rules, and most people would probably want to have the track as wide as possible in order to maximise the chances of getting the Center Line Score. As to the body, I cannot see any reason why it would make any difference. The speed at which the vehicle must travel is quite slow (at least is can be) so there is little likelyhood of instability due to high CG, understeer, oversteer or other slip angle issues. Aerodynamics will be virtually insignificant at the speeds required.
-Slender axle/tire track

Thanks for the help!
1. At regional and state competition you only have to ensure that the travel time is within the acceptable limits, less than 45 seconds. Of course you have to be able to predict the travel time accurately since that is 1/4 of the total possible point. At National competition you must adjust the speed to match what the event coordinator specifies.
2 As long as their voltage is labeled as 1.5 volts or less, you can use up to 4 batteries of any type you choose
3. As long as you don't lock up the wheels during breaking it makes little difference which wheels you use. If you are going to use the old screw and wingnut break then it should go on the front. It may seem a bit unintuitive but locking the front wheels on a vehicle (car for example) is less likely to cause an instability.
4. Weight is not factored in any way.
5. The rules this year make allow little choice of length and width. WHeelbase must be within a narrow range. Maximum track (measured to the outside of the wheels) is in the rules, and most people would probably want to have the track as wide as possible in order to maximise the chances of getting the Center Line Score. As to the body, I cannot see any reason why it would make any difference. The speed at which the vehicle must travel is quite slow (at least is can be) so there is little likelyhood of instability due to high CG, understeer, oversteer or other slip angle issues. Aerodynamics will be virtually insignificant at the speeds required.

nctarheel
Member
Member
Posts: 2
Joined: November 5th, 2008, 8:45 pm
Has thanked: 0
Been thanked: 0

Re: Electric Vehicle C 2009

Post by nctarheel » November 11th, 2008, 6:54 am

Thanks for all the advice! I will get to work on my EV immediately.

Protestant
Member
Member
Posts: 16
Joined: October 30th, 2007, 6:15 pm
Division: C
Has thanked: 0
Been thanked: 0

Re: Electric Vehicle C 2009

Post by Protestant » November 13th, 2008, 6:32 pm

Theoretically, you can make the vehicle as long as you want, if the front and back wheels are the right distance apart. However, I can't see a reason to make a vehicle longer than necessary.

captbilly
Member
Member
Posts: 94
Joined: April 17th, 2005, 11:06 am
Has thanked: 0
Been thanked: 0

Re: Electric Vehicle C 2009

Post by captbilly » November 14th, 2008, 10:37 am

What kind of time and distance errors (including lateral errors) were people getting last year? Does it require a 199.9 total score to win or is 195 good enough?

andrewwski
Admin Emeritus
Admin Emeritus
Posts: 954
Joined: January 12th, 2007, 7:36 pm
Division: Grad
Has thanked: 0
Been thanked: 11 times

Re: Electric Vehicle C 2009

Post by andrewwski » November 14th, 2008, 1:36 pm

All depends on your competition.

At nationals and probably quite a few states, I'd think you'd need at least 198. At regionals 190 might do it. All depends.

Post Reply

Return to “2009 Build Events”

Who is online

Users browsing this forum: No registered users and 0 guests