Ball Shifter vs other gearbox
 

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.

Re: Ball Shifter vs other gearbox
 

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?

Re: Ball Shifter vs other gearbox
 

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.

Re: Ball Shifter vs other gearbox
 

Re: Ball Shifter vs other gearbox
 

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.

Re: Ball Shifter vs other gearbox
 

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.

Re: Ball Shifter vs other gearbox
 

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).

Re: Ball Shifter vs other gearbox
 

I think it's important to be more specific here, since the OP may not fully understand the physics behind drivetrain design.

If you're pushing someone it's not simply because you're geared lower than them. It's because they either have "worse" wheels than you, are not geared to slip their wheels before stalling, or weigh less than you. I suppose you could add in geometry-if your bumpers are at the right height they could end up transferring a bit of their weight onto you, increasing your normal force.

It's certainly possible that someone could be able to push you (or at least stalemate, since you both should be slipping your wheels) with a single speed gearbox, if they had 6 CIM's, an identical base/weight, and were geared to go no more than 50% faster than you.

It's all about fuel efficiency.

Re: Ball Shifter vs other gearbox
 

In addition, a gear ratio that will get you really moving (15-18fps) may not help you at all if you can't accelerate quickly. In fact, you'll find over the span of 8-10 feet, there's little difference between a fast and slow drivetrain.

The improvements you'll see from a very speed drivetrain will only occur in relatively open field where you can use it. Most FIRST fields don't allow that, also 2013's was a nice exception if you were a low robot.

Re: Ball Shifter vs other gearbox
 

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

Re: Ball Shifter vs other gearbox
 

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.

Re: Ball Shifter vs other gearbox
 

Usually...skip to 47 seconds in. :D

Re: Ball Shifter vs other gearbox
 

Maybe some defenders, but not all defense.

Re: Ball Shifter vs other gearbox
 

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.

Re: Ball Shifter vs other gearbox
 

That looks a lot like when we were practicing in FLR and one of my friends on 3015 decided he'd try and play defense against us. He found out quickly that he wasn't going to win. We were still in high gear and were able to push them all the way across the field.

Keep in mind also, that a gear box with a lot of torque is great to push defense. HOWEVER if your wheels don't have enough traction they'll just slip and not be able to push. That is why the Vera Wheels from VexPro, with a gearbox that will make your robot have a lot of torque could push almost any robot. FRC team 771 played Defense against us in Qual 81 at GTR west, them having Vera Wheels, were able to keep us pinned easily. (1:45 ish in the video)