Passing a barrier

[bar]

Hello there Chief Delphi community
We have a competition within our team of games from previous years, and my group was given the task of 2012 'rebound rumble' and in the game was the barrier between the two bridges and I wanted to know what drive train do you think is Better to pass the barrier:
wcd 6x6 With 8 " Traction Wheels or wcd 8X8 with 6" Traction Wheels ?

thank you

[kevincrispie]

This is a bit of a false choice. Many teams were able to successfully cross the barrier using neither of those methods. Is this exercise designed at evaluating each of those methods or finding the best possible method for crossing the barrier?

[Scott Kozutsky]

I think 254 could pretty easily get over the bump with 8 3.25 in wheels in a long drivetrain. They used low friction plastic along the bottom of the frame as well.

I'd look into pneumatic wheels just for the fact that hard wheels really do put a lot of shock into the frame when going over the bump. IMO 1114 or 610 were the best at getting over the bump that year.

1114 was 6wd long with (http://www.andymark.com/Pneumatic-Wheel-s/309.htm) and some low friction plastic along the bottom and with a wedge in front.

610 you can easily see in the release video. (https://www.youtube.com/watch?v=-7BG...6CD3AB2A804025) 8wd wide with a wedge from their pickup and pneumatic tires.

[AdamHeard]

Although pneumatic wheels weren't required to cross the bump, if used correctly it was a clear speed advantage.

No one could cross as easily as 1114/2056 imo, and the seconds they saved add up.

[JamesCH95]

As with anything: the execution is considerably more important than the design.

[bar]

Originally Posted by kevincrispie

This is a bit of a false choice. Many teams were able to successfully cross the barrier using neither of those methods. Is this exercise designed at evaluating each of those methods or finding the best possible method for crossing the barrier?

Kevin this exercise was designed to find the best possible way for crossing the barrier . and do you have any examples for team who used different kind of drive train ?

and we prefer not to use pneumatic wheels because the possibility of different pressure in the tire what would cause different diameter of the wheels . so we will Stick to hard wheels . and if we stick to the hard wheels is a bigger diameter of the wheels will reduce the Shock ?

[the.miler]

There are many examples of different bump crossing methods from that year; do some research and you'll be richly rewarded.

I pulled a couple for you.

2056: http://youtu.be/DMt1Ju4ZsUo?t=14m31s
8 x 8" pneumatic wheel

254/971: http://youtu.be/G0Tb4dP2RmA?t=1m43s (254 and 971 used very similar mechanisms to lift the robot a bit before bump crossing)
254: 8 x 4" treaded wheels
971: 6 x 3.5" treaded wheels
(forgive me if I get the diameter wrong, I can never tell whether someone is using 3.5" or 4" wheels. They're all small to me)

971 "Behind the Design Document" that has some additional information:
http://www.fightingpi.org/Resources/...Team%20971.pdf

Also, what do you think defines the "best" bump crossing method? Using large wheels might, with the proper implementation, make for improved bump crossing . . . but there are tradeoffs to using large wheels as well.

For example, if your bump crossing method requires a high ground clearance (likely if you're relying on using large wheels, though that as always depends on implementation), you're raising the CG of your bot. That could be bad for accomplishing other more important strategic goals, such as balancing the bridge (critical for seeding points in 2012).

Just things to consider.

[JamesCH95]

Originally Posted by bar

Kevin this exercise was designed to find the best possible way for crossing the barrier . and do you have any examples for team who used different kind of drive train ?

and we prefer not to use pneumatic wheels because the possibility of different pressure in the tire what would cause different diameter of the wheels . so we will Stick to hard wheels . and if we stick to the hard wheels is a bigger diameter of the wheels will reduce the Shock ?

Perhaps, but you would have to know the compliance (mechanical stiffness) of the wheel. The vertical stiffness is not directly driven by the wheel's diameter.

For example: an aluminum AM Performance wheel is probably a lot less compliant than a rubber and plastic Colson wheel. I could see a 6in Performance wheel being stiffer than a 4in Colson wheel, but that is only my intuition.

[Matthew Lang]

This may or may not be relevant to your project but one thing people severely underestimate even for a small bump is a low CoG. This is 610's 2012 robot before it had any of it's upper mechanisms on 8 6" pneumatic tires.

https://www.youtube.com/watch?v=9CimvHu01Kg

[kevincrispie]

Originally Posted by bar

Kevin this exercise was designed to find the best possible way for crossing the barrier . and do you have any examples for team who used different kind of drive train ?

and we prefer not to use pneumatic wheels because the possibility of different pressure in the tire what would cause different diameter of the wheels . so we will Stick to hard wheels . and if we stick to the hard wheels is a bigger diameter of the wheels will reduce the Shock ?

Many people in this thread have pointed out some of the good ideas that came from 2012. I would recommend looking into the different designs used in Rebound Rumble for crossing the bump and analyzing their effectiveness.

In these kinds of exercises, it is important to not narrow down the design choices too quickly. There are many ways of crossing a barrier, and making sure you consider many options, not just two, will help you in this and any brainstorming/design process. For this task, I would encourage you to think about the problem a little more broadly. Brainstorm many different ideas, discuss them, research them, and prototype them if you have the resources. A lot of the teams that were able to cross the barrier effectively had many ideas at the start, analyzing and testing each idea until they came to a solution.

[Chris is me]

I feel it's really worth noting that a lot of teams (254 / 971 included?) used wheelie bars or other props to get the front of the frame over the barrier before any wheels contacted it. Not a lot of teams used 4" wheels and just drove up the barrier like it was nothing.

Center of gravity is of the utmost importance when climbing any tricky obstacle. You need to think about where your tractive force is being applied and where your robot weight is being supported in order to fully understand the problem. Try some free body diagrams.

[BBray_T1296]

Not exactly on point, but it must be noted that we crossed the bump fairly effortlessly on 4 6" mecanum wheels

The real (heavier) robot took a little extra effort and the wood-metal bump difference was a non-issue.

The wheel modules had built-in deflector plates at 45 degrees and the whole orange modules were made from either 1/8" or .09 aluminum (I forget). We damaged one module when we hit the bump extra fast one time, but it was a quick swap to the spare.
The rest of the modules had very little warp in the deflectors post-season, though some lost some powder coat.

I guess my point is that with careful design considerations, the nature of the wheels doesn't have to matter.

[artK]

One solution that I remember being fairly effective that year was 233's intake, which was curved to allow the robot to drive over the bump like this. If your theoretical robot were to have an intake (which most effective robots have every year), I would consider seeing if I could shape it to do that.

[Joe Ross]

Originally Posted by bar

and we prefer not to use pneumatic wheels because the possibility of different pressure in the tire what would cause different diameter of the wheels .

Given that many teams have used multiple pneumatic wheels in the past, do you think this should be a concern?

[VioletElizabeth]

We used what we called pop-up pistons that year. We built our normal drivetrain, and then added two pistons that drove free-spinning wheels. When we fired the pistons, they pushed up the front of the robot. We also had an angled front of the frame, which would hit the bump and then slide over. We did not have trouble crossing the bump.