Electric Vehicle C

[Mike4192]

Very nice. What kind of braking system were you using?

Main drive axle connected to the motor is a threaded rod. A wing nut continually screws down the thread as the car move until the wingnut eventually reaches a stop.

To set it, I just found the circumference of the wheels down to like thousandth digit accuracy, then do a bit of math, and I know how many turns I need exactly for a certain distance.

Since this is my last year doing science olympiad, I might as well post some pics of it after states, my school doesn't get to nationals.

[Dh258]

Very nice. What kind of braking system were you using?

Main drive axle connected to the motor is a threaded rod. A wing nut continually screws down the thread as the car move until the wingnut eventually reaches a stop.

To set it, I just found the circumference of the wheels down to like thousandth digit accuracy, then do a bit of math, and I know how many turns I need exactly for a certain distance.

Since this is my last year doing science olympiad, I might as well post some pics of it after states, my school doesn't get to nationals.

Thats what I used on our Electric Vehicle, but bought custom wheels with cablibration for rubberbands around it. At state I believe I was .2cm off, but the turning and time was so bad we didn't place

[sachleen]

Is any one having problems with two servo moters and runing them at the same time?

On my car, I have 2 servos spin one shaft. I had tried making them spin each wheel independently but that led to more problems than it fixed for me (car goes waaay off course even with corrections). But having two servos spin one shaft works fine for me.

[WrightStuffMonster]

On my car, I have 2 servos spin one shaft. I had tried making them spin each wheel independently but that led to more problems than it fixed for me (car goes waaay off course even with corrections). But having two servos spin one shaft works fine for me.

Ya I found out the hard way that using two independent motors is a really bad idea even though it makes sense on paper...

BTW gh that is a really really nice looking ev. I love the CAD and CNC work on it. If you dont win at least you will get major style points.

[sirup96]

I am a senior and this is the first time my high school has a Science Olympiad team. I have no knowledge of using electronic components like a board of education or micro controllers and servos. I am working a partner who knows a lot about this electronics and we are using a Boe-bot kit from parallax, and we need servos that turn faster. I know that we need the vehicle to go at most 10 meters in 45 seconds and we can currently get it to travel 8.427 meters in 45 seconds. How can we get the wheels to turn faster? We are using Basic Stamp 2 to code our vehicle and are using the Board of Education Rev C. if it helps. And we do not have a breaking system for our vehicle, is it a must because our vehicle is able to stop instantly. Any help would be great. Thanks.

You actually need to be able to go 10 meters in 15 seconds if you want to compete at Nationals. If you believe that Nationals is out of the question then 45 seconds will be fast enough. There are all sorts of ways to got your vehicle to go faster. The simplest method for a vehicle that is already built would be to increase the voltage to the motor/s. You can use a DC - DC converter to increase the voltage. There are ready made converters or you can build one fairly simply.

By the way that's some fancy measurin you've been doing (8.427 meters in 45 seconds). How did you get such an accurate measurement of time, did you have a built in timing circuit.

All you need to do is incress the size of your wheels to make it faster, what is your size wheels you have on it? If your servo makes one rotation with 3" wheels and then 5" wheels your covering more ground with 5" wheels the your are with the 3" but if you get 7" wheels (they are out there and kinda funny to see one your car) you lose a little control if you wheels are still curving. It stops because you have three gears in you servos box and when the power is off the first gear can spin the others pluse it has to move the weight of the car as well. This Basic stamp i know verry well, so what is your camands in it? I have a setup almost the same as yours so i think i can help. If you car is slow still try moveing you pulseout colser, "i think", i have to cheek my book to be 100%.

[captbilly]

We had regionals last saturday. My purely mechanical vehicle got a raw score of I think 197.23 and got first (from what I remember). Distance was 6.5 m, we were off by 0.5 cm and time was off by 0.6 seconds.

With the mechanical bonus added in, that gives me a score of around 198. Wonder what place that will translate to in states.

When you say you were off by 0.5cm, do you mean the distance score or total distance from the center of the finish line (Finish Line Score) or both added together? I am actually much more concerned about the Finish line score then I am distance or time scores. How do people aim the vehicle accurately enough to get sub cm Finish Line scores?

[sachleen]

I'm using different wheels this year. last year i used VEX wheels which are larger than the ones i have now but I think these will work better because I can just drill into them and make the hole larger if I (hopefully) choose to use a larger shaft. 1/8" bends WAY too easily.

[gh]

How do people aim the vehicle accurately enough to get sub cm Finish Line scores?

I'm using an aperture sight with a really small hole for magnification. Last year, I just aimed down the right wheels (they were supposed to be aligned), but that didn't work so well mostly because (a) the wheels could move left and right and (b) I am pretty nearsighted and couldn't wear glasses with the goggles I use.

Then I went to a scope, and that was OK. The magnification was too high though, and actually made aiming harder. Also, it's really hard to mount rifle scopes. Even with CAD work and fabrication, it's still a pain to make a perfect Picatinny rail to mount the scope on.

So this year I just made an aperture sight. One (small) hole in the back and a point in the front. The small hole more or less compensates for my nearsightedness and lets me focus on the front sight sharply. All I have to do to aim is center the view of the hole in my vision, center the front sight in the view, and then line up the front sight with whatever I aim at. This is how it looks through the sight:
710|26/FILE0006.JPG

Photos of the front and rear sights:
712|26/FILE0008.JPG711|26/FILE0007.JPG

The whole vehicle, now that I'm more or less done with construction:
709|26/FILE0004.JPG

[gh]

Anyways, how are people adjusting their vehicles for left/right?

For me, I'm counting on the design being nearly straight as soon as it's built, but also made it so that the chassis pieces can be distorted using screws so as to adjust for curve. My rear sight is fixed; but the front sight is mounted with three screws. The center one is fixed, but the left and right ones are in oblong holes and allow me to move the sight left/right for an angular aiming adjustment. If I find that the sight is not centered, I'll remove the center screw to adjust the front sight. So in this way, I can adjust for curve and aiming offset.

Trouble is, how do you tell if you're curving or if the sights are just offset?

I have a plan that involves practicing with a laser pointer, but it doesn't work too well.

[sachleen]

gh, I faced the same issue last year. I wasn't sure if my car was going straight and my alignment was off, or my alignment was good and the car was curving. In the end, I figured it doesn't really matter. I stopped caring if my car went straight as long as it ended on the mark. So if you just set your sight and leave it, adjust your car based on that and, as long as it ends on the mark, so what if it curves?