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
*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.
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:
resources (motors, machining time, battery current, materials $$$]) allocated to the drive train
reliability and criticality of failure modes (ie a shifter will automatically be less reliable [more parts to fail] and a failure -may- be critical)
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
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:
To run with the Big Dogs, You’ve Got to Shift
'Nuf said
*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.
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.
*Originally posted by Neal Probert *
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.
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.
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.
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.
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.
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.
**This year, on #1015, we have tentative plans to go with a dual motor gearbox. **
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.
*Originally posted by ChrisH *
**. 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. **
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.
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.
*Originally posted by sanddrag *
**Those bosch gearboxes are pretty fragile from our experiences.
**
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.
*Originally posted by magnasmific *
** and our matching, patented designed for the chiapuah motors. its shift on the fly, and extremely reliable. you cant do much without shifting. **
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…
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.
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.
