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.

I think shifting is a must. I hate to say this but some times brute force is the best way to the top. Shifting is definitely a must in my book. But if your goanna shift you got to try and make sure its dependable and yes you have all this power but you must make sure you have a way to transfer it all to the ground.:D

Yeah, same idea with us. We had six motors working together beautifully at one speed. We were faster than average and far more powerful than average. That is the Hexadrive(tm) in action. :) With six motors producing 2 horsepower, making a tranny would weigh us down and take up so much space that it wouldn't be feasible. In any case, with the mad traction we were getting off our wheels and off the weight of two goals, combined with our superior power, our strategy really didn't call for a tranny. That's why I'd argue that your strategy defines what kind of gearbox is needed.

HERE HERE!!!! I SECONDE!!!

jonathan lall.
IN your case yes it is a little simpler but think all that power you draw with fluffy we only had 2 (4 in all) motors on each side and we could barley last one match only those 4. on the other head yes ots simple but in order to get maxium speed and torque you need to either shift or have CVT. Cvt is a litle bit to complicated and not as reliable as shifting. We only had to gears and what we can do with those blows my mind. I dont mean to bragg but we were playing with fluffy.(last years bot totaly unchanged except for a few bolts) A few of our enginners wanted to see what she could do well, we had her climing a 60 degree angle like it was cake it felt like a stunt from the dukes of hazzard. But any ways, in a higher gear becuse we have so much traction we would have just stalled the motors and popped the brakerr or if we lost traction we would have just spun our treds at a high rpm and make no progress. Well becuase of a lower gear and shift on the fly all we had to do was flip a switch. this gear shifting gives us an advantage more power and lower rpms allowing us to get maxium power and never really loose traction and using the power curve to the best of it ability.

But 190 had a CVT last year, and it worked like a charm (so to speak). The automatic-transmission mode never really worked correctly, but even in manual mode, it allowed a lot of flexability.

personally it depends on the game and what ure robot will actually be doing, don't just build something for looks build it to be used, next years game thoug (2003) we will trying a new drive train sysytem we are currently testing out different designs for a transmission (speed etc. ) all we gotta do now is to get a few good men to actually stop being lazy and help the coaches assemble the system



hehe thats all i can say now

Yes, again going to strategy, our robot could not exert itself at full power for the whole match.

As for CVT, I'm not convinced it's as useful as it's made out to be. We were right beside 190 in the pits and gawking, but I personally think shifting is overrated.

In your case, I'd say you really need shifting, and it sounds like it ended up very well.

Shifting is a matter of dual function. If you want a powerful robot, there absolutely no reason to switch gears, it is the same if you want a fast robot. But since you can't have both at the same time, if you want both you have to be able to switch. You don't need a tranny to have a powerful robot, just thought I would make that clear. Shifting is only necessary if you want to be fast then powerful or vice versa.

We've been debating the "shift" vs "no shift" and "2 motors" vs "4 motors" on my team since the end of 2002's competition. We have not yet reached a conclusion!

However, the key debate points are:
1. resources (motors, machining time, battery current, materials [$$$]) allocated to the drive train

2. reliability and criticality of failure modes (ie a shifter will automatically be less reliable [more parts to fail] and a failure -may- be critical)

3. necessity to the game (ie if you cannot spare the resources and you don't need it for your strategy, it may cost you in other parts of the robot)

Our current position is:
If you want to engage in a pushing contest, it is essential to have four motors in the drive train and be able to shift into a very torquey low gear.

If you are really torquey but cannot move into high gear, you can be out-maneuvered in most matches.

I don't think we have the resources to engage in a brute force pushing contest at this point, so I doubt that we will go down that road.

The main problem which I have seen with many of the published shifter designs and which occurs with the Bosch gearbox is that they can get "out of gear." You can end up with no gear ratio in a failure. This seems to be too much of a drawback to risk those designs.

We have two designs (and whether we build one remains to be seen) which do not have this drawback. They default to the high gear (fast mode) in a failure. If we do build this, I'm sure we'll discover why this is a bad idea.:)

Another reason for a shifter comes from speed. Low gear gives you great acceleration. If you can shift on the fly, you will actually be faster in terms of time to objective, than a robot with a really high gear. This might rely on a vehicle speed measurement, which is difficult with the existing parts.

Do those of you with shifters on the fly do it via the driver or do you shift at a particular vehicle speed?

Andrew, Team 356

I don't know about all of you, but when i look at the design's for gearboxes and transmissions in the white pages and what i seen at nats last year, i seen a WHOLE lot of metal! That has to be a huge amount of weight to slap on a drivetrain! To maybe loose a little acceleration you could use a simple geared down (or up) shaft with a cupling and sprocket. Even if you wanted added torque, simply meshing in another motor wouldn't add up to the weight of a transmission. Keep in mind that a few ounces off a drive system is another few ounces available towards a mechanism.
Now i take this position on this subject because of last years game. We have a very muscular drive system on EL TORO, a VERY VERY muscular one that took up every ounce of weight available. Now, dopn't get me wrong the extra power was outstanding and we could push anything we tried, but as a result of the robustness we had no room left for a claw to get the goal. The reason for the power in the drive train was to push two goals. Now we over estimated the resistance in moving two goals at a time so by the time we finished the bot and tested it on a goal we realized how we didn't need even close to the amount of power we established.

POINT-- I would use the extra weight for a more practical use in the game.

IN response to all of you,
All of you have very good points, but depending on your strategy does truly decide weather you shift or not. We shift on the fly. It is up to our operator to shift, but we used sensors to make a shift on the fly so that we wouldn’t grind gears. I response to not having enough weight left over for our bot, we had a capability of grabbing 3 goals, but we ended up getting rid of that during the practice at regional. We ended up trying to add weight to our bot. and as you all saw we added our fly swatter on the last day at nationals. And we were still under weight

To tell the truth everything can be fixed with simple design changes. But there are just so many things having do with shifting or not. I stick with shifting.

To all,
Istill stay shift but in the end brute force always does bring you to the top or pretty close

To shift or not to shift
 

Shift, please do whatever you can in the off-season to develop a vesatile shifting mechanism, how nessescary it is can not be weighed in words. - Big Steve

Last year Team 60, the Bionic Bulldogs from Kingman, AZ had the following on their robot:

'Nuf said

I don't think 71 shifted (well thier feet shifted back and forth) and they did pretty good this year ;) Neither did 47, 67, 61 and many others. If you have the weight and your design allows for it AND you need to be fast and powerful (which I doubt we will see pushing like last year again as I think FIRST will move back to less contact) then shifters may be a good idea. I don't think it is a requirement for a robot.

Shiftless in Ann Arbor
 

If you have to stop to shift gears, it's not worth it. You only have a couple minutes in the contest and wasting time just shifting gears is not a good idea.

We tried it, with the shifter on the drill motors, last year on #830. With the servos linked to the clutch on the drill motors, it never really worked right.

We had to lock the clutch to prevent slipping and we eventually locked the drill into low speed. We could push around a bit and still get across the field reasonably fast.

This year, on #1015, we have tentative plans to go with a dual motor gearbox.

Re: Shiftless in Ann Arbor
 

It depends on your mission whether or not taking time to shift is a waste of time. It also depends on the length of time it takes to make the shift and how reliable your system is.

There's your problem right there, servos. A small pnuematic cylinder works much better for shifting if it is properly linked to the tranny. The pnuematics are also much faster and if all you are doing is shifting, you probably don't need the compressor either.

Locking the drill motor clutch should be standard procedure. If your low speed was still reasonably fast it was geared too high to start with.

Hope you're working on it already, not the real one, a prototype of course!

In spam 180s case we used a shift on the fly design and numatics to shif. they worked out well together. and the sensors desined to work with that reflective tape they work great in the shift on the fly area the drive train.

Re: Re: Shiftless in Ann Arbor
 

IN spams case that compressor was the most important thing on our bot, yes we also had a pnuematic goal graber but we shifted back and forth between gears at least 10 times in one match. we even broke our toggle switch to sift one but thanks to our driver who has long finger nails (he plays guitar) we were still able to shift.

Its worth it if you know how
 

i think that it is bsolutely necessary to shift during game play. our robot had 4 wheel drive, witht he technocats transmission desigm, and our matching, patented designed for the chiapuah motors. its shift on the fly, and extremely reliable. you cant do much without shifting.

Most of the fast and powerful teams shift these days. It is a necessaty to have a machine that has more than one configuration. The way that the games have a qualifying session and an elimination run, require you to have different strategys to be competitive. Most of the teams who were in the final rounds of the Nationals were bot's with split personality transmissons. To us this extra time and effort seems worth it.

We have been using the Bosch trans for some time now. This year is the first year we decided to shift. We however, decided to shift using servos utilizing the stock housing and shift ring--if anybody watched Team 27 in the pits, they usually saw us constantly going through that silly system! We like the compact size of the planetary system, although they do have more friction than a spur gear style trans.

To avoid the struggle of 2002, 2003 guaruntees we are using a Drag race inspired Air Shifter, also promises a new Aluminum trans housing. A new "Shift Ring" made of steel or brass. A one piece Housing for both the planetary sections and out put. If anyone has seen our trans assembly, then they have seen how we eliminate the clutch. I have all this drawn in AutoCad 14 as a 3D file. If anyone has any questions on how this looks or works I be happy to share some data.
:cool:

Re: Its worth it if you know how
 

Did you really patent it? Rock on T3.
Let me know when the FIRST royalties start flowing in.
Of course you'll have to pay 45 for using part of their design...
:p :D ;)

I've heard from some of you that change gears refer to the Bosch gearbox, do guys mind telling me what that is, since my team is interested in switching gears for this years competition :) Thanks!

The bosh gearbox is also referred to as the drill motor gearbox. it is pictured below. It has a shifting mechanism that uses a shift lever and two sets of internal planetary gears. High speed gives 1000 rpm and a stall torque of 10Nm and low speed gives 300 rpm and a stall torque of 29 Nm.

www.team696.org/motorspecs.html

For Rookie Teams...
We should remind everyone of the locking pawl in the drill motor transmission. There is a white paper on this board about how to remove that little tooth. With the locking pawl in place you are almost assured to breakout the transmission case during competition.

You know how hand drills have a little switch that makes it spin slower but more torque? That's what teams use in the drill motors to shift gears. What you couldn't see in the picture of the drill transmission, is a silver strip of metal that you can move back and forth to select either high gear or low gear. Teams usually use a servo motor for each drill transmission to move that metal strip to switch gears. I know some teams use pneumatics to do that as well.

There are planetary gears inside the drill transmission. The metal strip engage one of the ring gears that slide from one stage of the planetary gears to another. In High gear, that ring gear is in a position where it lock one stage of planetary gears together so that it act like as if that stage doesn't exist. When you switch to lower gear, the ring gear slide out and unlock that stage, adding further reduction to the transmission causing the output shaft to spin with a slower rpm, but higher torque.

Of course, this isn't the only way to do this. There were different transmissions I've seen in the past years, and the technokat's servo transmission is only one of them. There are other ways like
having another set of wheels on your robot with a different gear ratio, and you lower those wheels when you want a different speed/torque combination. I've seen this on 131's 2000 bot, and 258's 2002 bot. Changing wheels size is also a mean of switching gear ratio too.

There are also ones where there are two set of gears on the same shaft, and only one set is engaged at a time, and you use pneumatics to engage the other set of gears for a different ratio. I've seen this on 67's 2001 bot, and 45, 60 and 254's 2002 bot last year.

Then there were other teams who lower another set of drive train with a lower gear ratio, like 111 and 810 last year I believe.

But most teams use the servos to switch gears on the drill transmissions because its fairly easy to do. You just got to figure out a good servo mount on top of the transmissions, and make sure the linkage between the sergo output arm and the metal strip is good enough.

so, if we used the Bosch gearbox......would that, say, lower our speed or reduce our torque compared to having a gearbox that fully switched gears using pneumatics and stuff like that?? because I'm not sure how powerful these bosch motors would be compared to different gear ratios

also, how would we design the bosch motor to shift gears, if we were to use it as a shifting motor?? pneumatics?

bosch motors
 

It depends on the gearbox design you would use outside of the Bosch transmission. You can also find equations and charts on this site to help you determine the benefits and disadvantages of an external gearbox.

Check the previous replies. Some teams use pneumatics, others use the servo motors in the kit. I would also highly recommend that you do a detailed check through the white papers of this site. There are many different designs here, so look around. My team is currently trying out the most recent dual motor transmission design, as it looks very promising.

thanks for the help Alavinus the white papers helped a lot :). However, I'm curious on how some of the gear shifting robots were able to shift on the fly?? how did they make the gears mesh properly? and if they don't mesh properly what are the chances of those gears being destroyed?

gear meshing
 

I know in the transmission design we are thinking about, the edges of the gears are beveled to help them mesh with each other. This little step probably helps a lot and even if it did not, the gears are still steel and therefore pretty durable. However, if you are concerned about the gears stripping, you could just have your operators stop the robot before shifting, it really does not take that much time.

Instead of having the operators stop the robot, have you program do it, then you can reduce the shift time to nearly exactly what it need to make the shift every time. At least that's how I would do it

It seems to me that when you are shifting "up" (from high torque to high speed) you want to do this "on the fly" to take advantage of the first 1/2 second of excellent acceleration as well as the improved speed of your "high" gear.

I agree, when you are heading into high torque mode from high speed mode, you can (and should) do this at zero speed.

I would think that a hysteresis loop on speed command would cover the programming side.

It still doesn't answer what happens if you get "in between" gears, which still seems to be a potential problem with all the designs that I have seen.
Andrew, Team 356

Several of the transmission designs from last year (including ours, which is posted in the White Papers section) used pneumatic pistons to position the primary drive gear specifically to deal with the "gear mis-mesh" issue. If a piston moves the primary drive gear between the Low Gear and High Gear positions, then it acts as a spring if the gears do not perfectly mesh when they are shifted. If the gears do not perfectly mesh when the system is shifted, then the drive gear and driven gear just contact each other on their side-faces (beveling the corners of the gear teeth helps prevent any severe wear problems).

The piston/spring just applies side forces to the primary drive gear to hold it in place until the gears rotate sufficiently to properly mesh, then the drive gear drops into place. Again, beveling the corners of the gear teeth makes the meshing action even smoother. If this sounds confusing let me know and we can post an animation of the system that shows how it works.

On most long-term applications, which may typically go through millions or tens of millions of cycles, you would probably not do it this way. But in the type of systems designed for most FIRST robots, which are typically subjected to maybe a few thousand cycles, wear is not too big of an issue.

-dave

yeah, if don't mind dlavery would you post an animation on how it would work, because I'm not quite sure on two things. How does the pneumatic piston act as a spring?, because a pneumatic piston goes all the way in or all the way out. Also, how does the drive gears mesh?? teeth on teeth, or does the pneumatic piston slide the drive gear onto the driven gear sort of the like the design posted by team Epsilon/NASA

Ok, I keep hearing people saying that beveling BOTH gear faces helps with meshing. I'm assuming we're talking about chamfering the edge of the gear. Now, if we're talking about using beveled gears/miter gears/45 deg. gears, then just ignore the following post, cause it's based on a completely wrong assumption.

I understand how this would reduce wear on the gears by spreading it over a larger area. I fail to see how beveling both faces would help with meshing, however. I can see how it would intuitively seem that way, since beveling a hole and a shaft lets the shaft slide right in, but I think this is different.

The way I see it, gears meshing is all about getting the two gear cross-sectiobs to line up properly. By beveling both gears, you're merely enlarging the cross-sections that need to mesh. So unless there's friction going on to get the gears going closer to the same speed, I don't think beveling both gears actually helps.

That being said, I can see how beveling just one gear would help. By doing this, the straight gear must initially mesh with just a small part of the beveled gear. This would probably help, though the straight gear would get point ground off rather quickly. In addition, rounding off the edges of the meshing faces would probably help are well. Anything to change the initial cross sections that have to mesh.

This is, of course, all just theoretical, and based on my vision of how things should work, but it makes sense to me.

Don't limit your thinking to shifting gear ratios. In my opinion 71 did shift. They could move really fast on the back wheels and had tons of pushing force with the "walkers".

We did something similar without changing any gear ratios. We had a second set of smaller wheels that turned much slower than the main drive wheels. When we latched to a goal, our fast wheels were lifted off the ground and our high torque wheels were planted into the carpet. Using wheels that spin at different speeds where you can select which of them is contacting the carpet is the easiest way to "shift on the fly". Our OCCRA students (a 100% student built robotics competition) even pulled this off last year using only a hand drill and hack saw.

http://www.chiefdelphi.com/forums/at...&postid=108949

They may have had multiple drive systems, but they definately didn't shift.

There is a large animation file here (5.6Mb Quicktime file) of our drive design (with thanks to Team 151, from whom I borrowed the cool wheel design!). I will create a smaller version later and post it when I get a chance.

You are correct that the piston goes all the way in or out, but that is when it is unconstrained. The cylinder acts as a spring when it is mechanically prevented from fully extending. For example, when it drives a change gear up against a stop when the piston is only at half-stroke. At that point, the pressurized air inside the cylinder applies a constant force against the piston, which is maintained until the obstruction preventing the piston from completing the stroke is removed (or the pressure is released). When that happens, the piston resumes it's stroke until completion.

-dave

okay thanks dlavery, because my team is planning to use the gearbox posted by you. Well, sort of a similar design to it however, we're not quite sure on how some of the gears match up. Does part 30 mesh with 15, and parts 13 mesh with 14, on your download?? and if they do than what's the point in shifting because the drive gear is already being driven by the two motors and the gearing for the drive shaft will be the same whether or not you shift? finally, what would happen if we got rid of the drill motor part? would it still work properly and that it will just go slower and less torque?

Read the assembly notes carefully, particularly with regard to the elements you mentioned. It is important to note that the torque gears (14 and 15) are not connected to the drive shaft (17) - they just spin freely on the shaft. Their purpose is transfer torque (and reduce speed) between gears 10 and 30. The drive gear (16) DOES drive the drive shaft by engaging the enlarged key (20).

-dave

----------------------

Y = AX^2 + BX +C

OK they didn't shift. Their solution to having both a fast robot and a strong one (and they could switch between the two) wasn't by shifting gears but the end result was the same.

Shifting is NOT necessary if you have a system like this.

How would you classify systems that have wheels spinning at different speeds but geared off the same motors, where the driver can select which ones are contacting the carpet?

We had something similar to this, but instead of having different wheel sets, we had our primary drive as the wheels (speed) and we could raise/lower our set of treads for torque, the treads went up/down in about 6-7 secs, and we went about 2-3MPH on them, on the wheels we went about 6-7MPH......it was our solution for wanting both speed and power.....

How heavy was that?

Ok we at 88 used both sets of shifting. At the begining of the match we used drills to run out and grab a goal. The drill motors could be run on high or low. Once we grabbed a goal we would drop a wheel run on chippy's down and that would be used for tug of war. We decided to use this system because we knew that you need speed and at the same time you need power. So being able to do both was quite an advantage this year. I can't tell you how many times we stole goals from opponents or just shovved an opponent to where we wanted them. Last year this was the key and depending upon January 5 we will see if it is needed again.

okay thanks that's what I thought....anyway, we probably are going to make your gearbox or something similar to it, so you may want to a take our team down as a potential team who's building your gearbox design....thanks for the help! :)

With our dual planetary transmissions we had no problems going between hi mid and low speeds. They we're quite effective.