Transmissions

[Starke]

I would like to know what kind of transmissions team are using and how effective they have become.

Meaning: how many speeds (1,2,3,4...), is the transmission a certain kind(ex. killer bees 4 speed), and how often do you use it in a match. Has the transmission seemed to be necessary to have the speeds you have.

[Ryan M.]

Our team had a simple, one speed transmission. With 2 Chips on each side, it had plenty of power and speed.

[Kyle Love]

Team 45 uses an AndyMark tranny. It has two gears with a pneumatic shift. We used one CIM and one FP with a planetary gear box on it.

[jjdebner]

Team 195 uses a four speed transmission with 4 chips bases on the transmission from team 33. This transmission shifts using 4 one inch cylinders and we found it has plenty of power and speed.

[team222badbrad]

Team 222 the TIGERTRONS have used our "one of a kind" ball bearing shifting style transmission for the last two years.

This years transmission is a two speed shift-on-the-fly with one CIM per a tranny (for a total of two transmission and two CIMS on the robot). We have found that two drive train CIMS can still easily push around most four CIM drive trains out there. Our transmission are put to use continuously throughout the match.

Some situations we use our shifting transmission for:

(High Gear) speeding down the middle of the field

(Low Gear) basic game play, precision maneuvering, and when somebody gets in our path they will then become moved out of our path...

Last years transmission was a three speed shift-on-the-fly with one CIM per a tranny (for a total of two transmissions and two CIMS on the robot). Last year we really only used first and second gear. That is why we only used a two speed transmission for the 2005 robot.

Overall, our ball bearing style transmissions are very effective. They consistently shift instantaneously, they shift very well under load or under little load, and last but not least, they nearly leave a patch of rubber on the carpet when shifting from high gear to low gear at top speed.

Some other reasons why we like this type of transmission:

1. Nearly any number of speeds you may want can be built with this type of transmission

2. It is not all that hard to build and is a great way to teach students just how complex or simple for that matter, shifting gears can be.

3. It is unique to the FIRST world.

4. It is simple and effective!

5. We love getting the question: "How do you shift that?"

This years transmission can be seen here: http://www.chiefdelphi.com/forums/sh...2+transmission

Also you can find a heap of information on our transmissions here on ChiefDelphi by searching for "222 transmission".

[Cowmankoza]

coming to you from team 1251

we are currently using the kop gearboxes, however we switched the output sprocket to give it more speed, finding that our stratagy would work better with more speed

the only thing is a slight loss of power

it runs beautifully

[bradleym1559]

1559 found a way to use the kit transmission, and then program it to work at one speed and, at the touch of a button, kick into turbo...all software, no need to alter the kit trannys. Worked out nicely...everyone thought we had a slow robot...then hit turbo and it surprised them! We had awesome programmers this year.

[sanddrag]

Originally Posted by bradleym1559

1559 found a way to use the kit transmission, and then program it to work at one speed and, at the touch of a button, kick into turbo...all software, no need to alter the kit trannys. Worked out nicely...everyone thought we had a slow robot...then hit turbo and it surprised them! We had awesome programmers this year.

Many teams do this and I can't figure out why you would ever want to limit your power. Why not just give it all from the start? Yes a "tubo boost" may give a nice surprise when pressed but during normal times why in the world would you use the program to limit the capabilites of the mechanism? To me that seems foolish.

[Tristan Lall]

Originally Posted by sanddrag

Many teams do this and I can't figure out why you would ever want to limit your power. Why not just give it all from the start? Yes a "tubo boost" may give a nice surprise when pressed but during normal times why in the world would you use the program to limit the capabilites of the mechanism? To me that seems foolish.

Back in 2000, Woburn's Blizzard 1 had just such a control. But it wasn't included to surprise people--there was a bit more pragmatism involved! As it happened, that robot had front-wheel-drive (old Johnson drills) and rear casters, and because the weight distribution was very biased toward the rear, the robot had an annoying tendency to over-rotate when trying to manoeuvre. That button was in there so that full speed could be achieved if necessary (and usually with a fixed rear wheel deployed, raising the robot off of its casters), but under normal conditions, the robot wouldn't be so difficult to control. I'm not so sure it was of much actual use, though, since that robot was by far the worst-driving of any of the Woburn family (of those that I've taken for a spin, at least--that's the last six, plus one of the ancient Canada FIRST robots). It certainly wasn't an efficient or elegant solution, as sanddrag pointed out.

This sort of solution is only useful if you don't care about the power output (in 2000, we knew we had enough power to drive around at half-throttle), or conversely, don't care about the current and efficiency (we should have cared--we threw 30 A breakers on some occasions, that year, and were limited to a 60 A main fuse, not a 120 A main breaker). You're effectively decreasing the voltage of the motors--for instance, by half--which just doubles the current needed to sustain a certain power level. This is why it is fundamentally crazy to control something like a (DC permanent magnet brush) motor at low throttle settings (i.e. the Victor's output voltage is a fraction of the motor's rated quantity); you're just going to force the current way up, and the efficiency way down. Low efficiency just means heat losses, and to compound the problem, the internal fans don't work well at low speed.

So what's the right way? Shift gears. You'll have two speed ranges that allow the driver to avoid overstressing the motors by running them too slowly.

Of course, sanddrag already knows all of this, so I suppose that this is for everyone else out there....

[Mike]

Originally Posted by sanddrag

Many teams do this and I can't figure out why you would ever want to limit your power. Why not just give it all from the start? Yes a "tubo boost" may give a nice surprise when pressed but during normal times why in the world would you use the program to limit the capabilites of the mechanism? To me that seems foolish.

I agree, it's like only driving 1/2 speed for the whole match but when you need those few seconds at the end driving full speed. Why not just give it all from the start?

[sanddrag]

We made a 6 motor drive system with two speeds. I believe 188 Woburn did something similar in years past but I believe we are the only ones in the country with a 6 motor two speed this year. It's shifting mechanism is based roughly on the 2003 Technokats design. Everything has been beefed up (1/2" wide gears, 5/8" hex shaft, 1/4" sideplates) for the power of six motors. We could have gotten away with making it lighter and a little smaller but since this was our first year doing 6 motors or shifting, we decided to not take any chances. Since this worked with no problems whatsoever, we will be going smaller and lighter next year.

One nice thing is that al the reduction is done in the box to directly drive a 5.5 inch wheel. This is nice so you don't have to have the little sprocket - big sprocket thing going on.

Unfortunately, the way this year's game turned out to be played was quite different from what we imagined. We never really got to exhibit the drivetrain's full potential. But maybe that's just because the threat of it made opponents run away. In a game like 2002's Zone Zeal or 2003's stack attack, this gearbox would have been totally awesome.

While it was cool to have potentially the most powerful drive system in the nation, next year two of those 6 motors will probably be put to better use into an arm or ball scooper or something.

And just as a final note, having 6 motors is advantageous if your drivers can use them. We are geared for 15.5 fps (no load) in high gear and can still push a robot sideways (in high gear) without tripping any breakers.

[Max Lobovsky]

A software filter for the drive train is not a bad thing in itself, but a turbo button is not really the best solution. There is enough resolution in human movement of joysticks to be able to control any robot I have seen (We have a omniwheel holonomic drive with no feedback. It is likely one of the most difficult to control FIRST drivetrains that exists). All that is required is a good input/output curve. The only time a "turbo button" is actually neccesary is when the thing you are controlling actually has a wider raneg of outputs than you can reasonably input. The turbo button lets you effectively double your input range.

[UCGL_Guy]

Our team worked over the summer to ue 222's design - best shift on the fly made. After finally getting the bugs worked out they work beautifully. We stuck with the three speeds a low low a middle and a high.
Thanks to Brad and 222 -- we did modify and tweak your design somewhat and if time ever permits will share with others.

[Rombus]

Heres my whole take on the "Turbo Button" issue:
i would have set it up to be locked in high all the time then have a slow mode for Perscis movement to cap or get a tetra from the loading zone. We tried the 4 speed transmission this year but ended up having to lock it into 2nd gear and we did OK with it. I dint know the exact reasons why we chose not to go fully shifting, but i personally didn't see much of a need for a 4 speed tranny on such a small field.

[Dave.Norton]

Originally Posted by Max Lobovsky

We have a omniwheel holonomic drive with no feedback. It is likely one of the most difficult to control FIRST drivetrains that exists)

We used the same wheels, and after looking at your site it looks like we had an identical layout. One difference though, ours was very easy to control. When we prototyped it the drive wouldn't go in a straight line to save itself, problem with 3 points defining a plane, and four being over constrained. Which is to say every time it hit a bump it would steer into a new direction. By adding a rotational accelerometer and suspension to the platform we got it under control (little joke there) and now it is fun to drive.