Electric Vehicle C

[Jim_R]

Table of Contents:

• Battery discharge curves
• Voltage up-converter (several posts)
• Insides of a LEGO RCX
• Building a low-cost EV
• Basic EV design with pics
• Effect of internal resistance of motors and batteries on delivered torque
• Don't use sensors that track the floor, etc
• Buying CD Wheel inserts
• gh's microprocessor post A
• Why you want a large wheelbase/long vehicle
• gh's microprocessor post B

Original post:

Code: Select all

EV rules are relatively unchanged in 2009. EVs now have to be shorter and thus less accurate. Mechanical EVs now have slight bonuses, but I believe good electronic EVs are still going to do better. Anyways, I welcome these changes because they level the playing field, and it'll be be easier to find boxes to fit EVs into.

I think I will be using one continuous rotation servo (Vex gearmotors are based off of these) to belt drive a plastic chassis with a steel shafts/ball bearings/CD wheels "drivetrain." I'll probably switch the driving pair of the wheels to pulley/o-ring wheels at some point. I may use a rifle scope to aim, but I find that it's pretty useless.

So, what are your designs going to look like this year? Will you be using Vex or a robot kit or building your own frame? Are you going to use wingnuts, timers or optical encoders? How are you going to aim and brake the vehicle?

[sachleen]

i think I'm going the same way as I did last year. I may build a new frame, or use VEX since it curved predictably anyway.. As for the mechanical cars.. they will be less accurate but really good scrambler people may go that route.

just a random though: i found a box that my EV fits into

[andrewwski]

I'll probably go with a timer again...at least for regionals...it's not the easiest thing to do correctly (vs. microcontroller and servos) but it's a lot cheaper and if you can do it right, it works well.

[adam124218]

Gosh, I wish they'd had those mechanical bonuses last year. That's what my partner and I did, because we were both really mad they'd taken away scrambler. It turned out not so good--we got sixth at state, which was disappointing. Then the vehicle got 40th at Nats, which I guess was pretty good considering both me and my partner from regionals and state had conflicts and two new people ran the vehicle. Anyway, we should have gone electronic and just refused to do it. I got so fed up with electric vehicle, I'm switching to Junkyard this year.

[captbilly]

Is there going to be a bonus for using mechanical rather than electronic braking systems this year? I was wondering how that might work. Would an electronically activated but mechanical brake get the bonus? Would you need some mechanical means of measuring the distance traveled to get the bonus? It seems kind of silly to require the vehicle to be electric but then give a bonus for using non-electric braking and maesuring systems.

[Dark Sabre]

The "bonus" is for not using electronic devices. The wording of the rules makes it clear that electronic devices are things like chips and diodes and stuff, not motors/switches/etc. It doesn't look like it matters where you use electronics, you would still be excluded from the bonus.

There is not penalty/lack of bonus for building an ELECTRIC vehicle . They are just trying to discourage the use of microprocessors and the like to balance the playing field and encourage innovation.

[gh]

Oops, sorry about not being more descriptive in my OP. The rules themselves are pretty vague about how "electronics" is defined, but I think it's pretty obvious what counts and what doesn't. Electric circuits themselves with only electromechanical components (wire, switches, relays) obviously have to remain legal for the bonus to have any use.

[fleet130]

There is a distinct difference between "electrical" and "electronic"; however, that distinction is likely to be lost on many event supervisors/judges.

An attempt was made to include language to consider bucking/damping diodes as "electrical" rather than "electronic". I haven't seen the final published rules so I don't know if it was successful.

I've always found it interesting that judges in "real" science events are required to be subject matter specialists, but those for building events often seem to be just "warm bodies" that somebody found on a street cornet.

[Uncle Fester]

Street cornet? Anyone found on a "street cornet" has got to be pretty small-- heck, I couldn't fit on a street TUBA! Sounds uncomfortable, too. Great typo, Fleet. You're cutting into my territory, though. Bad typing is MY specialty!

Before I noticed the typo, I WAS going to comment on one "street corneR"-- When I moved from the Los Angeles area to Bloomington, Indiana back in '89, I was being shown around town & campus (Indiana University) by a friend. A Friday night, I was amazed that cruising was still a popular activity, and the sidewalks were packed (seriously packed) with HS kids. At one point, we come across a pack of about 30 punks, all in leather, chrome, and sharp objects. Walking past them, I noticed that they were discussing using PC I/O registers for controlling "something".

Pretty sharp street corner.

[captbilly]

If the final rules actually include a bonus for not using electronics, does anybody understand why they would do this? I always thought that working with microprocessors was one of the main purposes of the electric vehicle event. If the only difference between electric vehicle and wheeled vehicle is the electric motor vs. a rubber band or fishing pole, then it would seem that electric vehicle just become a simpler version of wheeled vehicle. There were wheeled vehicles 2 years ago that could stop within less than 1 mm of the finish line and predict the travel time more accurately than most judges could measure, it would be a shame to let those competitors simply repower those vehicles with electric motors and run them again.

Again, assuming the mechanical bonus really materializes in the final rules, does anyone have any idea how much of a bonus there is?

[fleet130]

I always thought that working with microprocessors was one of the main purposes of the electric vehicle event.

Just the opposite is true. It has been a struggle to prevent them from being banned. Microprocessors are viewed by many as an unfair advantage due to their "excessive" cost. They complain that a team with big bucks can just buy a microprocessor and off the shelf software, plug it into their vehicle and magically get a perfect score every time without having to do any work.(I make no claim this has a basis in reality).

assuming the mechanical bonus really materializes in the final rules, does anyone have any idea how much of a bonus there is?

The proposed bonus was 1/3 the difference between 200 and the final score if the vehicle doesn't use any electronics. Note that as the error approaches zero, so does the bonus! I don't have the final rules, but, to my knowledge, it hasn't changed. Can anyone confirm that?

[WrightStuffMonster]

I am pretty sure that you can get a everything you need to program an Atmel including the chip for around 15-20 bucks if you shop around. Sparkfun sells everything that you need to get started for somewhere around that. That is a weeks worth of coffees for your average teenager. If you can not afford you spend 15 for a micro you probably have some fairly serious issues with your ev. I would love to see that off the shelf software that allows ev to be a plug in and play affair. I have never seen anything like it. Thanks fleet for dealing fighting to keep micros in. That was by far the most educational part of the event was learning how to program micros well enough to make the ev go.

[Dark Sabre]

I always thought that working with microprocessors was one of the main purposes of the electric vehicle event.

Just the opposite is true. It has been a struggle to prevent them from being banned. Microprocessors are viewed by many as an unfair advantage due to their "excessive" cost. They complain that a team with big bucks can just buy a microprocessor and off the shelf software, plug it into their vehicle and magically get a perfect score every time without having to do any work.(I make no claim this has a basis in reality).

assuming the mechanical bonus really materializes in the final rules, does anyone have any idea how much of a bonus there is?

The proposed bonus was 1/3 the difference between 200 and the final score if the vehicle doesn't use any electronics. Note that as the error approaches zero, so does the bonus! I don't have the final rules, but, to my knowledge, it hasn't changed. Can anyone confirm that?

That is the correct calculation. The run scores are both based off of Distance Score + Time Score + Finish Line Score + Center Line Score + Bonus Score (which, if present, is calculated based on the sum of the first 4 scores).

[andrewwski]

That bonus seems fair...if you do good it won't depend on the type of vehicle.

But using electronics isn't necessarily expensive...I did a timer for less than $30...

[gh]

I am pretty sure that you can get a everything you need to program an Atmel including the chip for around 15-20 bucks if you shop around. Sparkfun sells everything that you need to get started for somewhere around that. That is a weeks worth of coffees for your average teenager. If you can not afford you spend 15 for a micro you probably have some fairly serious issues with your ev. I would love to see that off the shelf software that allows ev to be a plug in and play affair. I have never seen anything like it. Thanks fleet for dealing fighting to keep micros in. That was by far the most educational part of the event was learning how to program micros well enough to make the ev go.

This is true, but remember that you do need an optical encoder to interface the vehicle with the microcontroller, and a good encoder is not cheap. However, the Vex robotics franchise (I think I'll call it that from now on) sells reasonably good encoders, and you can get $400 industrial precision encoders used from eBay for under $20, which is what I did.

You also need some way of driving motors with the micro. This can be had for a few cents in MOSFETs, or could run up more than $50 if you buy a dedicated motor controller. I feel that modifying a $20 servo to continuously rotate (Google "continuous servo" for tutorials) is the best tradeoff in price vs. performance. That $20 will buy a self-enclosed, relatively tough gearbox and motor, with its own internal motor driver that can provide simple but precise speed adjustments, as well as braking.

Finally, throw in about 50 hours of programming, and twice as much time testing, and you might have a winning vehicle. My EV last year was pretty minimal, compared to the stuff I listed here. A lot of the stuff was surplus or free samples. Spending lots of money will save time, but spending money will not help you win.

Anyways, I usually justify my SO expenses to my parents by reminding them that I don't have a cell phone or video game console, and I haven't gone to the mall in years. Those are teenager stuff, right?