To shift or not to shift?
 

That is the question. Based on last year's game (Zone Zeal), do you think it is necessary or extremely advantagous to shift gears? Does it give enough benefit for the much extra time, cost, and risk involved? Please explain why too.

It really depends on the nature of the competition and the strategy of your robot; a yes or no wouldn't really be adequate. Last year, you could get away with a non-shifter (we opted for enough motors that we could gear up and still have massive torque) and focus on other things. We had an exclusive goal-grabber, but hybrids might find it advantageous to shift.

Last year we did quite well for a single speed drive. I was on team 93.

Our drive was simple. It was comprised of a sealed gearbox, which the Chiaphua motor connected to. This was then connected to a 3/8" chain and drove the rear wheels. The front and rear wheels were connected with 1/4" chain, making it 4-wheel drive. Overall, the drive reduced the Chiaphua motors 30:1.

We were using 6" diameter wheels I believe.

We found shifting to be quite useful.
In low gear, we were able to push with about 250 lbf.
In high gear, we could go about 12 feet per second and we were able to coast almost half the length of the field.
The complexity was worth it. But beware. You really need a good gearbox designer to make the thing work efficiently.
We still had a few bugs in the system, but we should have the Mark III gearbox ready to go this year.
Maybe four speeds. Or a clutch so we can coast farther. The possibilities are endless....

By shifting to a lower gear ratio, you add more torque to your robot. Say the Drill motors, if you only have 2 drill motors, by shifting you could double the torque from them. Playing against another robot with 2 drill that doesn't shift gear into a lower gear ratio, you would be able to push them around if your robot have good enough traction.

However, assuming your two robot have equal traction, if the opponent doesn't shift gears, but have 4 motors instead of two, then it have enough motor power to push as strong as you do, while not having to reduce speed at all.

Its all a very tricky balance between traction, torque, and motor power. You pretty much got to have more of everything if you want to put push your opponent.

Just look at some of the major players last year. Team 308 and 60 both lift up 2 goals completely off the ground to get major traction. 71 had the walkers with major traction and pushing force, and they grab three goals at the same time making it hard for some teams to grab two goals at once. Other teams like technokat 45, Hot bot 67, and many others had a shifter too.

But of course, traction and torque wasn't everything. Look at some of the major ball robots, like 173, 175, 157 (I think aztech have this number), 121, and others. They had a fast robot that could get lots of balls quickly, and were able to make those balls count. Unfortunately, against strong pushers, goals they grab on would to eventually be pushed back.

But then again, it was very important to have a fast robot too. Kingman (60) had a really high speed a high gear, and they were able to get to the goals before others, gaining control. Same thing with Gila Monster's (64) robot. They had a very smooth swerve drive with 4 motors, and they dominated the field by driving around smoothly quickly putting their robot in use when needed.

It's always a question on strategy... Last year, it ended up the strongest pushers could dominate the game easier than others.

Nicely put Ken L.


I can't think of anyone that epitomized a good transmission any more than 180, SPAM.

In high gear, they could make it all the way accross the field in a few seconds. I know they did this to us in the einstein finals match. In the last 3 seconds they kicked it in high gear, and started driving to their end zone (from their goal zone). They coasted all the way back into their wall.

In low gear, they could out-push many robots out there. They did a nice number on Beatty in the finals matches.

Another point....
 

I think shifting is a must, but shifting to a lower speed doesn’t always have to be done for power either. You could have slower speeds dedicated for maneuvers that require more precision and if u had shift on the fly you could just pop it back into a higher speed right when u got done.

For the first time ever my team (84) had a shiftable drive system in the 2002 games. For our first five years competing, we have always had very rugged and strong robots. This year with much request, and the great need for it with our strategy, we finally used a shiftable transmission. Without this, we would not have had the great success we had this year. Our engineers our currently working on a 'shift-on-the-fly' mechanism for next years game. I know that our base driver wouldn't trade being able to shift for anything no matter what the game is.:rolleyes:

other benefits
 

The TechnoKats have been shifting gears since 1999.

We see these benefits:

1. Of course, there is the combination of power and speed.

2. When we run in high, we usually are pulling more amps through the electrical system and causing the 30amp breakers to start breaking out. This would usually happen about 1 minute into the match. When this would happen, we would switch to low gear and the amp pull would be less, saving our breakers. (this took place when we used 2 motors to drive the 'bot)

3. In low gear, not only do you get more power, but the robot driver can control the position of the robot more precicely.

I am a big fan of switching gears, even if it's by using the Bosch gearbox.

Andy B.

Those bosch gearboxes are pretty fragile from our experiences. The steel gears look okay durability- wise but we've cracked the plastic housing before. And I don't know about those plastic ring gears. And then there's the whole clutch thing that's just a real pain. Has anyone been successful shifting with the bosch gearboxes? If so, some pics or descriptions please.

Also, can I hear some more views on this topic from a team that has never had a shifting robot?

Thanks.

sanddrag
We have not used shifting to achieve our drive systems. Our mechanical engineer designs the drive transmission to have a desired speed/torgue at some particular RPM. Then we achieve that stated RPM in software so that it is less than full speed (at the motor) most of the time. This allows us to select a "turbo" mode which is near full speed on the motors when high torgue is not needed. We do have multiple drive motors, this year four for a four wheel drive and two additional for a tank high pulling/low speed drive that would lift the other wheels off the ground.

Here are a couple of white papers.
 

Here are a couple of designs used by many teams. When used correctly, the Bosch gearbox can do just fine... just be careful to be fully stationary when shifting gears.

TechnoKats home page

Go to the "Resources" page.

Look at the "Single Motor Gear Switching Assembly" and the "Dual Motor Gear Switching Assembly" white papers.

This single motor assembly (or a derivation of it) has been used by over 50 (maybe 100?) FIRST teams.

Andy B.

So what's the end result. Go with the Bosh or build your own???
Mr. Ivey

we have been shifting for 2 years now...
 

Shifting is a must

The only problem with shifting is that there are many things that can go wrong

Example:

At Brunswick Eruption, our robot got mad at us because we left it outside in 30 degree weather, in a box, overnight. As soon as we got there we fired it up and our gearboxes went sreeeeeeecch. We use servos that are mounted right above the gear selecter on the bosch drill gearboxes. Everything in programing had to be just right and everything mechanical had to be just right. I think the cold messed up something up in our mechanical design, because metal expands and contracts. So it took us a while to get everything just so again...........

We are working on a shifting on the fly mechanism for this year like no other, so be afraid, very afraid!!

Badbrad

Shifting is not needed in all applications.

Some of the shifting gearboxes I have seen cost a huge penalty in weight where a medium speed multiple-motor drivetrain would also work very well. Team 61's tank drive was one of the strongest last year and it was only a single speed.

One thing I didn't see very much of is lightening of the steel gears. We removed 70% of the weight of each of the steel gears and had no failures all season. With the amount of steel I saw in some of these drivetrains it's a wonder the robot made weight after you add manipulators.

For swerve the only multi-speed bot I have seen so far is the Thunder-Chickens and man you better be pretty ambitious if you are going down that road behind them.

Shifting is cool, and it helps in many applications but you can also design around it like Al said.