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  #16   Spotlight this post!  
Unread 17-11-2003, 23:38
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Quote:
Originally posted by Victim of Fate
Yea...getting back on topic, this information is helping me correct for an extremly high ratio on the transmission that was giving me numbers like 93mph, Im going to gear it down again to bring its max speed closer to 25mph

thx all
Are you sure that transmission will put out enough torque to make your robot...oh, I don't know...move?
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Unread 17-11-2003, 23:43
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Quote:
Originally posted by Victim of Fate
Yea...getting back on topic, this information is helping me correct for an extremly high ratio on the transmission that was giving me numbers like 93mph, Im going to gear it down again to bring its max speed closer to 25mph

thx all

don't you think that might be a little steep? 25's machine was almost 14 ft/s, and it was one of the fastest bots out there. 25 mph is about 36 ft/s by my calculations, so unless you're anticipating some really beefy motors, you're going to have trouble accelerating up to top speed.
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Last edited by RogerR : 18-11-2003 at 00:28.
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Unread 18-11-2003, 00:15
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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
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Unread 18-11-2003, 08:13
Victim of Fate Victim of Fate is offline
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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.

Last edited by Victim of Fate : 18-11-2003 at 16:27.
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Unread 18-11-2003, 12:06
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Rc car

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


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Unread 18-11-2003, 12:26
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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.
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Unread 18-11-2003, 14:56
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CVT's -- nice idea, but unproven benefits...

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.
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Unread 18-11-2003, 15:40
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Quote:
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.

Last edited by KenWittlief : 18-11-2003 at 15:44.
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Unread 18-11-2003, 16:24
Victim of Fate Victim of Fate is offline
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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

Last edited by Victim of Fate : 18-11-2003 at 16:27.
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Unread 18-11-2003, 18:21
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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.
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Last edited by Gope : 18-11-2003 at 18:23.
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Unread 18-11-2003, 19:09
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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)

Last edited by KenWittlief : 18-11-2003 at 19:12.
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Unread 18-11-2003, 22:37
Victim of Fate Victim of Fate is offline
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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.
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Unread 02-12-2003, 22:46
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Re: Top Speed

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.
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  #29   Spotlight this post!  
Unread 03-12-2003, 13:29
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Re: Top Speed

The Wildstang robot has been designed to go about 7 ft/s top speed for the past 5 years. We have used 2 drill and 2 Fisher Price motors for the drive for the past 3 years. We have convinced ourselves that with the power of these motors, this is about the optimum gearing for speed versus torque if you do not have a shifter (we never have done a shifter – why would be the subject for another thread). Anyway, at this gear ratio, we can accelerate a 130lb robot pretty quickly. And when you have “crab” steering, this is about as fast as you want to go for control reasons. We use another technique to reduce the sensitivity of the controls for “fine motor skill” maneuvers – we cut the PWM output to the motors in half when the trigger on the joystick is not depressed, and set it to full PWM output when it is depressed.


I will say that if we decided to use more powerful motors (the Chips instead of the FP’s) then we could bump up our top speed accordingly. This is why 25’s Evil Machine, which used 6 motors for their drive, was effective at a higher top end speed. But yeah, at those speeds, the drive control sensitivity is very high and thus difficult to control the robot.

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Last edited by Raul : 04-12-2003 at 07:37.
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Unread 03-12-2003, 21:27
Victim of Fate Victim of Fate is offline
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Re: Top Speed

I should of made this clear earlier.

My mentors got sort of edgy about me talking about my transmission. Maybe at the end of the season ill be able to show everybody.

PM me if you want to talk more about it...away from prying eyes.
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