Electric Vehicle C

[jazzy009]

sorry i cant answer your string break question, i have one of my own though.
i am using a scope and the rules say scoping devices need to be permanently attached to the vehicle. has anyone used a scope before at a competition? if so, how was yours permanently attached? i dont want to do anything to damage the scope (say hot glue??) so i was going to tape it.

[andrewwski]

Yes, I used a scope.

I built a frame out of basswood sticks and ty-rapped it down. Then I aligned it and hot glued it.

Hot glue doesn't really ruin it, you can pick it off pretty easily when it's cold.

[fleet130]

do I need a stop lever

A brake is used to make the stopping time and distance more reliable/repeatable. If you don't need it, you don't need it. Only you can answer the question.

the rules say scoping devices need to be permanently attached

I believe the intent of "permanently" to to remain attached throughout the competition. Applying a little common sense (I know this may be asking a lot), supervisors should be able to come to the conclusion that "permananent" is hardly attainable (if the hot glue can be peeled off, it is not "permanent"). Unfortunately other interpretations are easily made. To receive a definitive answer, this is something you really MUST ask of your tournament organizers.

We only use 2 batteries at a time. Every 5-6 runs we switch a set.

Back in the Battery Buggy days we only ever used 2 sets of batteries in total while preparing for and during the tournament.We always ended up in the medals, often in the top 2. Granted, the vehicles were always as light as possible.

[Aia]

Does anyone have the winning EV scores from Nationals last year (top 6)? If you could post the scores, it would be greatly appreciated.

[Untitled]

Fleet,
So how did you keep the battery voltage constant to get consistent times if you only used 2 batteries?

[fleet130]

So how did you keep the battery voltage constant to get consistent times if you only used 2 batteries?

Note: We uses 2 "sets" of batteries, not 2 batteries. We didn't even worry about voltage. Just used the maximum allowed, swapped them with the second set before every run, kept the vehicle weight as low as possible (requires less power to move) and used "D" cells (conditioned before use them) for maximum current capacity and life so they stayed as much as possible in the linear portion of their discharge curve.

The physical size of a battery greatly determines its internal resistance, current capacity and total power that it can supply over its lifetime. Larger batteries have less internal resistance, can supply more current and have more capacity than smaller cells.

"Conditioning" gets the batteries past the first part of their discharge curve where the voltage drops rapidly. It consisted of making a few runs to discharge the battery a little. You probably need a few runs to adjust the steering, brake etc anyway. If not, just throw out the data for the first few runs, or better yet, compare it to the next few runs to see how much difference there really is.

The internal resistance climbs rapidly when batteries are required to supply a high load(current). Swapping batteries after each run allows them to recover and keeps the internal resistance lower. Keeping the weight down requires less current and reduces the increase in internal resistance.

Keeping the weight down uses less power, but it's easier for the vehicle to hop and lose track of direction or distance. Keeping the speed down helps in this respect and has the added benefit of decreasing the effect of small timing errors on the score.

Making fewer runs also keeps the batteries from discharging. I don't think we ever made more than 50 runs total. Calibration consisted of five runs at each of 5 distances AFTER the bugs were worked out of the vehicle. Fastest and slowest for each distance were thrown out and the remaining were entered into a high school level statistics computer program. Regression equation from the program was then used to interpolate the results for all possible distances. Note: This assumes the vehicle can produce repeatable results before starting calibration. This process produced consistent results over 198. Scoring was slightly different then, so I'm hot sure how that would score today.

That's all I can think of for now!

[sachleen]

sorry i cant answer your string break question, i have one of my own though.
i am using a scope and the rules say scoping devices need to be permanently attached to the vehicle. has anyone used a scope before at a competition? if so, how was yours permanently attached? i dont want to do anything to damage the scope (say hot glue??) so i was going to tape it.

I always understood that to mean that as long as you don't set your car down, put the scope on it, align it, take the scope off and then run your car, you're fine. As long as the aligning device(s) stay with the car the whole time you should be alright. (just my thoughts, not necessarily what your judge will think)

[rman]

Does anyone have the winning EV scores from Nationals last year (top 6)? If you could post the scores, it would be greatly appreciated.

I'm sorry I can't answer your question exactly but I also have one of my own, along the same lines.

As an attempt at your question; I believe the top electric vehicles were getting high 198s to low 199s, but I do not have the exact answer.

My additional question is, how were the rules changed from last year to this year? I didn't do the event last year so I don't know if what the rules were or how they have changed. Is the rule about the Event Coordinator picking the velocity of the vehicle at Nationals (actually inverse velocity, seconds per meter vs meters per second) new this year, or did the vehicles last year also have to be able to adjust their velocity to a number given by the Event Coordinator. The reason I am asking about the rules changes is that if the velocity was not picked by the Event Coordinator last year then comparing scores from last year's National competition would not necessarilly be meaningful.

I will do some more research and see if I can find last year's scores.

[rman]

The only scores I have been able to find so far were some from last year at a regional competition. One team got just over 199, there were a couple in the 198 range and then they dropped off pretty fast from there.

I had a question about how the score is calculated. I have the manual and I think I understand the calculation but I would really appreciate if someone could confirm a sample calculation. Let's say you do a run and the vehicle pointer ends up 3mm short of the finish line and 5mm to the right of centerline, the predicted time was 40 seconds and the actual time was 40.05 seconds. The distance given by the Event Coordinator was 10 meters. The distance score looks like it would be 99.97. The time score would be 49.94. The Finish line score would be 39.96. I will assume that this run would get the center line bonus (although the vehicle could have crossed the line and come back), so the team gets 10 points. That totals up to 199.87, is that the correct way to calculate the score or did I do something wrong?

[fleet130]

Target Distance = 10meters
Distance Traveled = 9.997meters
Distance Score = [(Target Distance - |Target Distance-Distance traveled|)/Target distance] x 100
= [(10meters - |10meters - 9.997 meters|)/10meters] x 100
= [(10meters - |0.003meters|)/10meters] x 100
= [(9.997meters)/10meters] x 100
= .9997 x 100
= 99.97

Note: If the Distance Traveled is less than the target Distance, the distance score is simply:
Distance Score = (Distance Traveled/Target Distance) x 100

Predicted Time = 40seconds
Actual Time = 40.05seconds
Time Score = [(Predicted Time - |Predicted Time - Actual Time|)/Predicted Time] x 50
= [(40seconds - |40seconds - 40.05seconds|)/40seconds] x 50
= [(40seconds - |-0.05seconds|)/40seconds] x 50
=[(40seconds - 0.05seconds)/40seconds] x 50
= [(39.95seconds)/40seconds] x 50
= 0.9988 x 50
= 49.94

Note: If the Actual Time is less than the Predicted Time, the Time Score is simply:
Time Score = (Actual Time/Predicted Time) x 50

I think there's a mistake in your Finish Line Score. Basically, you lose 1 point for each centimeter the pointer is away from the center of the finish line. If the pointer is 0.5cm from the center of the finish line, the score would be 39.50. I'm not sure how you arrived at a value for the Final Distance. This distance is measured between 2 points, the center of the finish line and the location of the pointer on the vehicle. To find the Final Distance in your example, it is necessary to calculate the length of the hypotenuse of a triangle with the two sides given (3mm & 5mm)

Final Distance = sqr root ( 0.3^2 + 0.5^2) = sqr root (0.09 + 0.25) = sqr root (0.34) = 0.58cm
Finish Line Score = 40 - Final Distance = 40 - 0.58 = 39.42

Center Line Score = 10

Total Score = 99.97 + 49.94 + 39.42 + 10.00 = 199.33