To shift or not to shift?

[FatNick]

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.

[jonathan lall]

Originally posted by Matt Reiland
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.

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.

[DaBruteForceGuy]

Originally posted by FatNick
I think shifting is a must. I hate to say this but some times brute force is the best way to the top.

HERE HERE!!!! I SECONDE!!!

[FatNick]

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.

[ahecht]

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.

[mtaman02]

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

[jonathan lall]

Originally posted by FatNick
jonathan lall.
IN your case yes it is a little simpler but think all that power you draw

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.

[Eric Bareiss]

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.

[Andrew]

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

[DaBruteForceGuy]

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.

[FatNick]

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.

[FatNick]

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

[Steve Team 311]

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

[ChrisH]

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

To run with the Big Dogs, You've Got to Shift

'Nuf said

[Matt Reiland]

Originally posted by ChrisH
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.