A shifting transmission is not necessary, but they sure do bring in the technical awards!
A shifting transmission is not necessary, but they sure do bring in the technical awards!
I don’t disagree there. For example an iron block is very simple and very robust. Strap a control system on it and it will meet the requirements of being a FIRST robot. However, it sure doesn’t do very much, nor is it innovative.
Robustness is good, but a competitive robot must also be capable. A consistenly winning robot must be more capable than its opponents.
A shifting transmission is only one way to make a capable drive system. It happens to be a popular one, and with the proliferation of good shifting designs (and now commercially available ones), it’s a relatively easy one to use.
i think if your team can do it then its worth it! but a half working one is still worse than a fully working single speed !
Many people ask “Why should I have a shifting transmission?”
A better question may be “Why not?!”
I see many advantages in having a shifting transmission. Most of the technical aspects from the mechanical side have been covered, so I will give my pros and cons from a programmers perspective.
Reason 1: Having a shifting transmission and a well written program will enable your robot to be “smart” For example, lets say it is autonomous mode. Under normal conditions in high gear, the drive motors draw ‘X’ amount of current, and output a corresponding ‘Y’ amount of speed. Your robot collides with another robot and a pushing match begins. Your program senses that the amount of current going to the motors has increased, and the speed has decreased. (A considerable amount) Your robot could then know to shift to low gear and beat out the other robot. And for what I know of the mechanical aspect of this situation (probably not much), by going to a lower gear you can output more torque while drawing the same amount of current.
Reason 2: Creating an option to shift also creates another form of control. Whether this is controlled by the drivers or the robot is entirely up to you. Don’t be quick to jump the gun and assume that drivers always have to control your shifting transmission. We have the resources in our KOP to create an “automatic” manual transmission (a manual transmission that is shifted by the computer) I believe team 33 did this last year, but i may be wrong. This can give you a good advantage, and your robot will deliver speed and power when needed, respectively. Now I’m sure there is some way of achieving the same goal with a 1 speed transmission, but most people (like me) just dont know how and will default to what they know, such as shifting transmissions for changes in power and speed.
**Reason 3: **Its sexy.
There’s one more subtle issue that I think is worth pointing out. Say you’re designing a robot for Zone Zeal in 2002, and you want to make a ball pickup robot that tows the goal around behind it. Assume that you can make a robot with a 1-speed gearbox that goes 10 feet per second and can slip its wheels just before stalling, and that your driver is good enough that uncontrollability is not an issue.
From most of the posts above, this would seem to be an ideal drive system - but I would argue that there is still an advantage to having a shifter. Say your wheels slip at 90% of stall torque, and you can pull a goal at 80% of stall torque. Yes, you can pull the goal, but at that point you’re running too close to stall to get max power output - if you geared down slightly, you could pull the goals around a lot faster. It won’t help you push another robot (traction is still the limiting factor) and it won’t help you get to the goals faster, but if you’re towing a goal around for a large part of the match, it could still be very useful.
I am with Jay on this one. I have said it many times before: 2002 ruined a lot of us by making us think shifting is a neccesity. In 2002 shifting (of some sort or another) was essential because you could transfer over 360 lbs to your robot base (two goals at 180 lbs each. you 3 goal grabbers are excluded from my argument). 2003 and 2004 did not need shifting if you had at least 4 motors driving your drive base. I bet some teams did fine with two motors and no shifting, but 4 or more without shifting was plenty.
Speed and accleration are key and the race to the middle depends on both. Don’t make your high gear too high or your acceleration will be horrible. If you do not shift during the race to the middle (goals, end, whatever) then there is not much difference in time between a 12 fps robot and a 8 fps robot (with the same motors driving). Teams like the Killer Bees who have an automatic transmission are taking full advantage of shifting with automatic speed/torque based on current speed of the output.
We shifted in 2002 and 2003, but not in 1999, 200, or 2001. We will not shift in 2005 unless we can transfer weight to our robot.
I think the transmission issue depends on the robot itself. For example, an auton hanger (like 190, that uses the ramp and then hooks on to the bar) doesn’t need a transmission (except when facing 716 ) on the wheels. During design session, I suggested a robot with a transmission on the arms to cap quickly, and to use power to hang. A crazy smallball robot may even use a tranny on the small ball mechanism. It all depends on the type of robot. For this year’s game, I would suggest trannies for the wheels, since it was a robust pushing game.
Good thread…I agree with many points stated above.
No, you do not need to shift.
Yes, it is a good option to have.
Team 33 has make multispeed robots for many years.
As the kit had gotten better and the motors have gotten bigger, the need to shift has diminished. If you tried to get your 1999 robot to go 12-15 ft/sec you could not do it without a shifter. Now you can simply brute force the issue by throwing tons of power at it. I still like having a shifter for a couple of reasons:
Regardless, shifters are a detail. The major items of FIRST are still what they always were…understand the game, build a reliable quality machine to play it, train you drivers to use it to its full potential. If you do these things, you can win with or without any specific machine feature.
I would just like to ask a slightly different question:
How many national champions had shifting transmissions?
I can’t think of any. Apparently there is more to it than the drivetrain (beside in 2002).
173 - 2002 had a shifter.
They shifted the drill transmissions with a servo, if I’m not mistaken?
Still Raul… your point has been well made.
I may be incorrect but I’m almost positive that 469 2003 also had a shifting transmission…
But Raul’s point is well taken, I can list off a ton of bots just off the top of my head that have performed very well without shifting transmissions
2002 Divisional Champions without Shifting Transmissions
71, 144, 64, 25,
2003 Divisional Champions without Shifting Transmissions
292, 236, 175, 341, 25, 494, 111,
These are just teams off the top of my head…I can’t guarantee 100% correctness…
I’m a firm believe that shifting transmissions are great to have, but they certainly aren’t a guaranteed winning bot, a good driver and a good mechanism will take you far in any game.
469 shifted in 2003
Having a shifting transmission has it positives and negatives, on the positive side you can slow the robot down if you need to make a slow and precise movment, negatives are that there are more moving parts which means more things that can break and go wrong
Geez, how could I forget that about our 2003 partners?!
well as for breaking apart… most of the times if the shifter is messed up or something you can just lock it in one stage… and then its basically just a heavy dual motor drive system… i can’t really think of much more going wrong with a shifting tranny … now a planetary drive … yes
the only competition I have seen was the '04 competiton, where I co-piloted for our team, 1425. We did not shift. We did not have time to put together a tranny, but our team leader would have really been tickled if we could. I personally didn’t see a reason for a transmission. In the '03 competiton, I could see why speed was required (a lot of space, a race to get to the top, ect.) but in the '04 competiton, I didn’t see a reason, because there wasn’t much room to get up to speed, and there wasn’t anything that could have been taken back with some shoving. (not a FIRST-encouraged manuver, but these things happen.) I totally agree that it depends entirely on the competiton and what you are doing. Like I said, I am a rookie, so my test pool is minute, but I think generalizing about whether or not you need a transmission won’t get you anywhere.
Our teacher put it this way. Their is always an advantage to shifting. But is expending the extra resources to build it worth the advantage?
The rules specifically indicate that pushing [shoving] is OK and expected. Why would you say it’s not FIRST-encouraged?
This is, in fact, the main reason for a low gear in a transmission.
Actually, last year we used our low gear for climbing so that we could avoid all the pushing and shoving. But with the dynamics of last year’s game we felt that anybody who got into a shoving match, was probably doing the wrong thing. The 02 and 03 games were a different story. There was a lot of space to cover and you had to be able to hold your ground when needed.
Design for how you plan to play the game. If you need two or more clearly definable speed regimes, then shift. If not, then don’t.