Ball Shifter vs other gearbox

[Priyesh69]

I am trying very hard to convince our mentor to buy a ball shifter. Right now we are using a cimple gearbox with two cims on each. He doesn't think that going from a 4.67:1 ratio to 3.667:1 will change something big. Plus,he think that a low gear will be useful to pass defending robot. Does someone have any more argument or prove that ball shifter are really useful. Is there a vid showing a robot with ball shifter passing through defending robot.

[DonRotolo]

I agree with your mentor in that the two different gear ratios between a CIMple box and high gear of a ball shifter can easily be compensated for with sprockets.

What your mentor is missing are the advantages of having two gear ratios. We generally set our high speed ratio to a slightly faster than usual speed. That leaves our low speed far stronger in pushing power than anything else on the field with a single speed gearbox.

Watch any of our matches. You'll see that we get from one end of the field to the other very quickly but if someone gets in our way we can go right through them in low gear.

Of course, not every game needs two speeds. If you consider that every drivetrain is a compromise between speed and power, having two gears lets you enjoy far less of a compromise. Why do you think that cars are coming out with nine speed gearboxes these days?

[connor.worley]

Unfortunately, there's no special type of transmission that will magically get you past defense. The best way to deal with defense is to practice, regardless of gearing.

[Gregor]

Originally Posted by connor.worley

Unfortunately, there's no special type of transmission that will magically get you past defense. The best way to deal with defense is to practice, regardless of gearing.

No gearboxes will zip you right by defence, they wont even see you!

[Priyesh69]

Just to confirm getting the second stage(high gear) with a 3.667:1 ratio will get us to roll at a speed of 14 fps if the weight of the robot is 115 lbs. Can someone link the website where to buy the mentioned encoder.

[Gregor]

Originally Posted by Priyesh69

Just to confirm getting the second stage(high gear) with a 3.667:1 ratio will get us to roll at a speed of 14 fps if the weight of the robot is 115 lbs. Can someone link the website where to buy the mentioned encoder.

What chain/belt reduction (if any), and what wheel size?

http://www.chiefdelphi.com/media/papers/2755?

This paper will help you calculate it yourself.

Originally Posted by Priyesh69

Just to confirm getting the second stage(high gear) with a 3.667:1 ratio will get us to roll at a speed of 14 fps if the weight of the robot is 115 lbs. Can someone link the website where to buy the mentioned encoder.

For the most part, weight won't affect your top speed (it would affect how quickly you can accelerate to that speed, but not the top speed itself). What matters is the motors used, the gear ratio between the motors and the wheels, and the wheel diameter.

Also, if you're looking for a way to get around defense, while shifting helps, a 115 lb robot may have trouble pushing a 120+ lb robot. If you want to get around defense, I'd suggest clean and quick driving and evasive maneuvers. Just drive around them. If you want that extra oomph, you can shift, or make a 6-CIM drive (if it's legal next year). A 6-CIM drive will allow you to accelerate quickly enough to speed around defenders even at a decently high speed, plus gives you a bit more torque for pushing (note: Most 6-CIM drives will not give you more torque than a shifting transmission, but sometimes you don't need it).

[Jibsy]

Originally Posted by Gregor

No gearboxes will zip you right by defence, they wont even see you!

Oh man, I forgot about that one. It's taking every bit of self control I have to keep myself from bumping that thread.

[akoscielski3]

Here's your biggest problem. You are designing your chassis months too early for next season. You need to find out what your ideal speed/speeds will be. Your strategy may not require even going around defense next year, like this year if you were a FCS you didn't have to be really fast, but a cycling robot needed to be really quick.

Next year when you are designing your robot think of the strategy you have come up with. Design you drive train around that, your wheels, speed, and gearboxes should reflect you decisions.

For example I will explain our reasoning behind our speed, wheels and gearboxes this year. First off our wheels, we wamted to have a low profile robot that would rather then running over discs, would push them out of our way. That is why we chose lightweight small 4" IFI Traction wheels. The small wheels also helped with acceleration because you didn't need to move as much weight when moving. Next the speed of our robot needed to be really fast, but then again we needed to have a lot of torque to push around defense. We chose 2 speeds, 14ft/s and 6ft/s. This was achieved by using a 15T sprocket from the gearbox to a 20T sprocket on the wheels. We then had to decide on gearboxes. We wanted light weight, shifting gearboxes, that would achieve our goal speed, thus we chose Ball Shifters. (Keep in mind that the sprocket sizes were selected after the gearbox so we could get that desired speed.)

If you want to use ball shifters you should have a reason for the gearing amd shifting. Otherwise stick with simple gear boxes.
If you need more help feel free to PM me about it.

[Pauline Tasci]

I have to agree with Aaron, how do you know what your ideal robot is if you don't know what you need?
FIRST gives you six weeks to build a FULLY functioning robot.
Not just everything but the chassis.

As well I do not think it is a bad thing to become familiar with different drive systems, it will give you more options next year and you will expand your knowledge. But designing something for next year and not knowing what you need might set you up for failure.

[akoscielski3]

Originally Posted by pauline589

I have to agree with Aaron, how do you know what your ideal robot is if you don't know what you need?
FIRST gives you six weeks to build a FULLY functioning robot.
Not just everything but the chassis.

As well I do not think it is a bad thing to become familiar with different drive systems, it will give you more options next year and you will expand your knowledge. But designing something for next year and not knowing what you need might set you up for failure.

Exactly.
Also I never mentioned, though Pauline did, that offseason is a good place to practice things, like new transmissions. If you've never used two speed gear boxes then I suggest getting a pair of Ball Shifters and testing them out. Program them the way your driver would want, learn to find the best gear ratios, etc. Hopefully this will help you design you drive trains in future years.

[Mark Sheridan]

Originally Posted by akoscielski3

Here's your biggest problem. You are designing your chassis months too early for next season. You need to find out what your ideal speed/speeds will be. Your strategy may not require even going around defense next year, like this year if you were a FCS you didn't have to be really fast, but a cycling robot needed to be really quick.

Originally Posted by pauline589

I have to agree with Aaron, how do you know what your ideal robot is if you don't know what you need?
FIRST gives you six weeks to build a FULLY functioning robot.
Not just everything but the chassis.

As well I do not think it is a bad thing to become familiar with different drive systems, it will give you more options next year and you will expand your knowledge. But designing something for next year and not knowing what you need might set you up for failure.

Originally Posted by akoscielski3

Exactly.
Also I never mentioned, though Pauline did, that offseason is a good place to practice things, like new transmissions. If you've never used two speed gear boxes then I suggest getting a pair of Ball Shifters and testing them out. Program them the way your driver would want, learn to find the best gear ratios, etc. Hopefully this will help you design you drive trains in future years.

I think his methodology is correct. Determining which speeds would be ideal for this year should yield a system to determine speeds for other years. Consequently, 766 and 3309 design drive systems to accept a range of gear ratios using data from previous games. We also have a range of ideal gear ratios that work for most years. Hence why 1114's kit-bot on steroids is so good.

You both touch on practicing drive trains, I would add testing. 766 ran their drive train last year through an off season event and more. So this year 766 and us had great confidence in the drive's durability. When running a new gearbox, things you have to ask, does the rest of my drive promote durability? What will break first, the wheel? and what sort of preventative maintenance you need?

I don't think you can design your drive train too early. Having the extra time invested to promote durability is well worth the effort. As long as you factor in reCADing during the build season, making adjustment to reflect the new game and time it takes to build a drive, I don't see a strong enough argument against starting a design now. I started next years drive during week 6 of the competition season.

[Craig Roys]

Originally Posted by connor.worley

Unfortunately, there's no special type of transmission that will magically get you past defense. The best way to deal with defense is to practice, regardless of gearing.

Usually...skip to 47 seconds in.

[Siri]

Originally Posted by Craig Roys

Usually...skip to 47 seconds in.

Maybe some defenders, but not all defense.

[Craig Roys]

Originally Posted by Siri

Maybe some defenders, but not all defense.

I know...I just like the clip. In defense (no pun intended) of the Chimeras; we just happened to catch them right and once they broke traction there was nothing they could do, but we did have a nice powerful drivetrain with a low cg this year.