Reading through all the threads about 3 bot balancing I’ve seen a lot of teams with a narrow front robot talking about how they can turn sideways on the bridge and do a 3 bot balance. My team is one of those narrow front bots so I’m looking for as much info as I can get to make it happen.
Specifically I’m wondering;
-Has anyone ever seen this plan work? (video would be awesome)
-Is the turning bot usually the first or second bot on the bridge?
+If the narrow front bot is the first bot and it’s balanced after turning can other bots easily get the bridge down?
I’ve seen plenty of turning on the bridge, but not to triple-balance. A zero turn radius and an omnidirectional drive is probably essential to pull this off.
We have an 8-wheel drive, middle two dropped, and though we have not accomplished it at competition, we have been abe to turn sideways while maintaing balance.
Why would omnidirectional drive be essential? If there’s a sideways bot on the bridge, surely the other two could push it into position - especially with the low-friction HDPE. If there’s one thing we’ve learned about balancing, it works best when only one robot is moving.
In my experience thus far, pushing a dead-weight robot that is turned sideways on its wheels up a polycarbonate slope is harder than it seems. So I guess I’d say “essential unless you have a monstrous drivetrain and very good traction on the polycarb”.
Where is there low friction HDPE? The polycarbonate on the bridges is quite grippy against many types of rubber wheels. That includes the kit wheels from this year, last year, and also any pneumatic wheels that may be in use. I can tell you right now, with pneumatics in the middle and omnis on the back of our bot, there wasn’t a team we met that could push us sideways on a bridge (especially uphill).
I can’t remember who it was, but I did see this in action on a video on CD, they turned as they got to the end of the bridge. The only issue there is being sure that you don’t get hung up on the field wall and lost your balance points.
Geared down 45:1 with four CIMs and roughtop tread we couldn’t push many robots up the bridge even in line with their wheel base; that is to say, as long as our back wheels were on carpet we had no problem, but as soon as all four wheels were on the bridge we needed a little help. Rubber wheels likely would have worked better, but I still think it would be nigh-impossible (though not actually impossible, of course) if the robot was perpendicular to its wheel base.
We could do the math, of course, to find out what torque would be necessary – though we’d need the coefficient of friction of both the pushing robot’s wheels on polycarbonate, and the pushed robot’s wheels.
We are looking to implement something similar to this for Mount Olive. With our 6wd tank drive we can get roughly a zero degree turning radius. This would allow us to turn on the bridge for a triple balance. For this to work we would need two other wide bots on our alliance, and one with a great drive train. It would require the weaker bot to knock down the bridge and go up first, followed by us (we would need to be fully on the ramp before we could turn), and than have the strong robot push our robot into the center.
Obviously this is a perfect scenario and their are a lot of factors that play into this…but it should be interesting to see what happens at Mount Olive.
There are plenty of examples of long base bots being part of triple balances without turning sideways as an end position bot. In fact if your bot’s CG is biased toward front or back you will take up less room (+/-23" vs +/-28" for a wide bot) on the bridge if you just “let er hang” with lighter end of bot hanging over the edge of the bridge.
When 3456 triple balanced in Utah (albeit on the practice field), we were successful with two long robots and one wide robot. My team drove up first and turned sideways at the far end of the bridge (we are about 104 pounds with a true zero degree turn radius). The wide robot came up the middle, while the long robot, the heaviest of the three, helped to hold the bridge down while slowly pushing the middle bot forward. They ended up hanging off the back, but it worked!
I feel turning sideways is a viable strategy, with the right robot. We’re almost 6 inches shorter than max length and have two wheel drive, so it worked well for us and probably would for similar robots. Still, at least one wide robot seems to be required to pull it off.
I didn’t see it in person, but the San Deigo Regional alliance of 1661, 599, and 2599 used turning after being on the bridge as a fundamental part of their triple-balancing technique.
Video of a triple-balance where both 2599 and 1661 turn sideways (1661 at the last moment, high on the bridge) can be seen at http://www.youtube.com/watch?v=8T8B9f_YQpY
Our mecanum drive can do this - drive up the ramp, balance and pivot in the middle. It is pretty quick. We have the Andymark HD wheels which have a little better grip than the standard wheels (seems like). They are even tough enough to go over the bump quickly.
Or the mecanum drive can turn (into the wide side parallel to the edge of the bridge) and strafe while the bottom robot pushes the other robots up.
That goes without saying if you don’t have traction on your alliance, you lose (which I find is incredibly hard to do because there are so many robots with great traction).
6WD 8" pneumatic zero drop here - we’ve turned quite easily on the bridge during home practice, balanced or unbalanced, but not really with other bots on there at the same time. I’m not sure we can be pushed anywhere once sideways - never bothered asking anyone else to try!
We’ve thought before about meaningful ways to hang one side of the drivetrain off the edge of the bridge…that’s a scary thought! We’ll keep thinking.
Our team has a mechanum (AM 8") drive train this year, and we are easily able to turn on the bridge while maintaining balance. However, we have found that it has been difficult for other robots to push us up sideways, despite our omni-directional drivetrain. It is tough to do.