Top Speed

[Cory]

you wont have trouble accellerating, youll have trouble moving even if you could move, theres no way in heck youre going to be able to control a robot at those speeds.

Cory

[Victim of Fate]

All of you bring up good points, and i do sound like a total idiot now that I look back, but I my of left out several important details...

Its a new kind of continuously variable transmission...

Well, thats top speed, and I dont want to sound all secretive, but its lowest speed is about as extremely low as its top speed is extremly fast.

[team222badbrad]

FYI

I have a gas powered RC car that goes 40 MPH and I doubt that it will reach a speed of over 25 MPH before it would hit the wall, starting at the other side of the field. It weighs 10 pounds and has a 1.6 horsepower engine


Bad Brad

[KenWittlief]

A continiously variable transmission is a great idea.

The motors they give us can put out around a half a HP, if you keep them in the center of their RPM range. Look that the speed and torque VS current curves for the drill motors and the Chalupas.

problem is we start off at zero - the motors put out very little power at 0 RPMs.

I like this idea you have - I think it could be even better if you could find a way to keep the motors spinning at their optimal power output (midrange of their speed curve) and then vary the transmission ratio as commanded by the driver for speed. in other words, you would have a closed loop sensing the motor speed, and holding it constant through the Victors output, and the driver would vary the transmission ratio, not the motor speed. the performace (acceleration, pushing power, and top speed) of a setup like this would be phenomenal!

Im looking forward to seeing your published ideas on this.

[Joe Johnson]

While I love the idea of continuously variable transmissions, in practice, I have never seen one that is robust enough, cheap enough and small enough to make sense on a FIRST robot.

I can get behind a shifting. I MAY even get behind shifting on the fly (though I am clearly on the fence about that cost/benefit ratio given the fact that you can make a fairly simple 2 speed shifter from the drill transmissions as long as you are willing to write a bit of shifting code and can live without shift on the fly). I could perhaps be convinced (though I doubt it) that a 3 speed transmission could be a net benefit.

BUT... I really question whether a CVT is going to buy you more than it costs (in terms of power savings, complexity of design, engineering effort, etc.)

But... ...it is a free competition... ...knock yourself out.

Joe J.

[KenWittlief]

While I love the idea of continuously variable transmissions, in practice, I have never seen one that is robust enough, cheap enough and small enough to make sense on a FIRST robot.

Translation: Nick - if you have an idea for designing a continiously variable transmission, and its something you invented yourself

then you should reconsider posting it on a website

You may have invented something extreemly valuable (that could be patented) in which case, if you post it on here, or disclose it anywhere before its patented, you just gave your idea away for FREE!

If you are using principles for a CVT that you got from someone else (another team, a website...) then go ahead and post your ideas.

[Victim of Fate]

Sorry about the edit up there...

The transmission I am talking about is my own design, but it is a second generation concept based on a design myself and several other people sketched...

Both are unique but the both use the same concepts..

sorry again

[Gope]

While the fastest I remember are 2002 Kingman - around 18fps and 2003 team 25 - around 14 fps.

However, one thing to remember is your driver isn't as good as he thinks. Team 25's driver last year was in my opinion about as good a driver as first has ever seen, and he was barely able to control their robot last year. So, unless your driver is a god then having a robot over 10-12 fps is almost useless. And for most drivers 8-10 fps is pushing it.

[KenWittlief]

I agree - if your bot is really fast, then you dont want it driven open loop - you need a 'flight control algorythm' - feedback on the steering, limited braking...

WOOP WOOP WOOP! Altitude Altitude Altitude! :^)

Hey Nick - if you really think you have come up with a new invention or an idea for a system that can be patented, then this is what you should do.

1. Get a notebook that is bound like a book, like a composition notebook, and write you idea in there as best you can explain it - use drawings or whatever else to document your concept.

2. date and sign the pages, and have someone who would be able to understand the concept (a teacher, an engineering mentor, maybe a physics teacher) also sign and date the last page.

3. Start doing a patent search ( I think you can do this on your own on the internet for free) to see if someone else already has your idea patented.

4. if you dont find anything out there like your idea, then its time to talk to a patent attorney, and begin the patent application process - this will get expensive quickly and its not something you can do quickly.

remember - you dont have to actually build a working prototype to get a patent - as long as the idea is sound (you cant get a patent for gibberish).

PS - about your new signature... <= (just kidding :c)

[Victim of Fate]

Thanks for the tips. Ive already drawn everything out and Im having a (trustworthy)friend CAD it out for me.

I happen to know afew patent attornys so they might be able to help me out.

[The Lucas]

I'll tell you what I tell everyone who attempts to build a really fast drive. Watch your current draw! When motors stall it will wreak havoc on the electrical system. The battery will max around 300-400 Amps and the voltage will drop horribly. I experienced this firsthand with 2002's MOEhawk which had direct driven bosch motors in high gear (probaly ran about 20 feet per sec but accelleratin was slow). So monitor the current in the protoype phase to save yourself a lot of hassle later (we had to regear during competition). You have a CVT so make sure you keep it geared down while accellerating or pushing. Most of the impedance that limits current is not the internal resistance of the motor but the emf generated by the spinning coils in the magnetic feild. You might want to use an encoder to determine wheel speed and then let the program decide gearing. Good luck.

[Jay Lundy]

We've been experimenting with a fast robot with an offset center wheel. We did it for the smaller turning radius (less resistance to turning), and we did it rather than the omniwheels because we were worried about being too easy to push sideways.

Anyway, it sure is fast, and with our transmission it can be fast and weak or slow and strong, but we have run in to one big problem: it is nearly impossible to control.

When we turn the robot, it only turns on the center wheels, and it flies at about 1 rev / s. That may sound good but it makes it impossible to control. Luckily they improved the controller this year, so we're working on a positioning system, most likely with the 300 deg / s gyro from Analog Devices (with increased range) and optical encoders on the wheels (at least, that's what I'd like to do).

If we can get it working, I'm hoping to create a control system where the driver pushes the joystick in a certain direction and the robot turns to that same orientation and drives forward with a speed proportional to the joystick's distance from center. We may also experiment with other ways of driving.

Basically, my point is: speed is good, but make sure you design something that can be controlled by a human.

[Victim of Fate]

Originally Posted by Jay Lundy

When we turn the robot, it only turns on the center wheels, and it flies at about 1 rev / s. That may sound good but it makes it impossible to control. Luckily they improved the controller this year, so we're working on a positioning system, most likely with the 300 deg / s gyro from Analog Devices (with increased range) and optical encoders on the wheels (at least, that's what I'd like to do).

Hmm...does it only turn on the center wheel?
If it was able to steer using the other four, i would recommend that the center wheel be used for quick turns ie. push a button and you get an immidiate 90* turn left or right. But if you could get it so that it steers the way you describe, it should be pretty neat. I think that i know a trig equation that could help you out, but i dont know if it would work with the "C" language(im a pbasic kind of guy).

[KenWittlief]

I would try closing the steering loop with the yaw rate sensor that FIRST supplies - It may seem slow, but you very seldom need to spin your bot around quickly

and the fact that your bot can turn that quickly, means you have a lot of gain available, which will allow you to close the loop with the yaw rate sensor and have the response be very tight

this is one of those concepts that are hard to explain - to be very accurate and precise, you system needs to be powerful - more powerfull than necessary for the task you are trying to perform

then you can use a large amount of negative feedback, and the response will be quick to your commands - not that it will turn quickly, but that it will quickly do exactly what you are commanding it to do.

so if you move the stick slightly, and want the bot to turn very slowly, it will immediately begin to turn very slowly, and it will continue to move very slowly at the same precise speed, no matter what gets in its way (other bots, obsticals)

to put it another way, you must have great strength in order to be gentle.