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-   -   Hinged Bumper Design? (http://www.chiefdelphi.com/forums/showthread.php?t=41117)

JVN 02-01-2006 23:12

Re: Hinged Bumper Design?
 
The bumper is a 4-bar linkage.
As a mechanisms dork, I love any usage of 4-bar linkages.

From JVN's Top-10 list of 4-bar linkages in FIRST:
#1 - Team 308's goal grabbers from 2002.

-JV

greencactus3 03-01-2006 00:19

Re: Hinged Bumper Design?
 
Quote:

Originally Posted by JVN
The bumper is a 4-bar linkage.
As a mechanisms dork, I love any usage of 4-bar linkages.

From JVN's Top-10 list of 4-bar linkages in FIRST:
#1 - Team 308's goal grabbers from 2002.

-JV

oh you would love our past 2 years of OCCRA robots then. contact iheartpi for pics or videos of them she might have.

im just wondering how light you can make these..

greencactus3 03-01-2006 00:20

Re: Hinged Bumper Design?
 
oh btw how is that shifting? just tensioning and slacking a belt? one for high one for low?

Philip W. 03-01-2006 03:35

Re: Hinged Bumper Design?
 
Quote:

Originally Posted by greencactus3
oh btw how is that shifting? just tensioning and slacking a belt? one for high one for low?

That's right! To further understand how it works, there are a few items that need to be highlighted.

1. The gearbox, duh.
2. The cylinder on the left that controls the shifting.
3. The different size (that create different ratios) timing belt pulleys on the output shaft of the gearbox.
4. The chain that connects all three wheels of one side.

The gearbox has two positions, left or right.

Left position - belt and pulley furthest from gearbox is tensioned, drives right wheel at high speed, which drives all wheels.

Right position - belt and pulley closest to gearbox is tensioned, drives left wheel at low speed, which drives all wheels.

The timing belt that is not tensioned is dragged along at the same speed as the tensioned belt, likely because of the large size of the pulley on the wheel or wheel shaft (the belt would rather loosen around the smaller pulley).

CraigHickman 03-01-2006 11:47

Re: Hinged Bumper Design?
 
Might I second the request for a little specs on the design?

For someone on the team:

Was it worth the weight/design time/space?
How effective was it in game?
Would it be worth modifying to make lighter/smaller/more effective for future years?

Ianworld 06-01-2006 02:43

Re: Hinged Bumper Design?
 
Team member has arrived! I was talking to phrontist earlier about this so finding a whole thread devoted to our "Magic Bumpers" is pretty cool.

So some details about it. The idea as you guys seemed to gather was to take a pushing robot and cause it to lift its front up. It definitely worked to a certain extent which is to say it was like all mechanisms on FIRST robots, it had its pros and cons.

That video wasn't just a once in a case situation, it was very repeatable and in all of the cases where I was close enough to see them in action they seemed to work. As for the effectiveness in the competition, probably due to our wheel and tread set up, the most common effect of the bumpers was to cause both the pushing robot and my team's robot to just lock into position. This was especially true for when we were pushed from the side. I think with some better tread(gum rubber just worked funky in our six wheel set up) it would have been a much more useful addition to our robot. There were some problems that came up with them however.

The bumpers after we slashed and cut their weight to really as low as this system can go in this configuration averaged about 2 pounds per side. At that weight they were relatively fragile for a piece of the robot that was going to get smashed repeatedly(The backing of the foam was changed from steel grate to aluminum decorative mesh, for example.) My team has always been full of people working hard in the pits so constantly repairing and replacing the beaten up components happened every couple of matches without much noticing, but compared to the smooth reliability of many great bots the amount of work we put in maintaining the bumpers would seem extreme I think.

The second issue was that to make weight we also stripped off the pneumatic controlling mechanism that can be seen in that video(although its not shown in use.) Instead we used an ingenious knot dreamed up by a former girl scout on our team. At the start of the match, another mechanism on our robot would pull out the knots dropping the bumpers into position. It weighed nothing saving us the 3-4 pounds that the pneumatic and its parts added to the bot. The knot however had its own issues: hard to tie a complicated knot and if it didn't come out our stacking mechanism would become tied down.

So to answer those last three questions.
1. It was definitely worth the design time and as for space it just sat on the rim of our bot. With a really tough drive train and better treads it also would be worth the weight.
2. I listed its effects above, but I would say that due to the lack of tons of contact in last years game it didn't get to be used as often as previous years.
3. We really pushed the design hard, and had an amazing team of students working on it. So it is going to stay in our repertoire of tricks. Whether or not we'll use it again depends on the game, our robot and all the other factors.

Just some other notes about it. I should tell everybody that we did remove the bumpers halfway through our second competition. The reasons behind the move are long and complicated. By nationals(our third competition) we had a flop down wedge on the back of our bot, and the bumpers stripped of their hardware and locked into basically the up position. We initially designed it to be a clean wedge in many ways. It can't really tip a robot over and its clever, however this comes at the cost of being heavier and more complicated. Ironically, it also is most easily defeated by a wedge, which can use the very spring force in the bumpers to lift us up.

Anyhow if you want to make them, they're a lot of fun, you'll get a bunch of looks at competitions wondering what on earth all that hardware is for. Some things to look on improving: Bracing the corners is tough and they were always getting bent for us. Finding a lighter, stiffer backing for the bumper material that doesn't crack but just deforms under high loads. Finally thinking of clever ways to integrate them into your chassis, instead of slapping them on top of the kit set up.

If you have any more questions feel free to pose them, I'll keep an eye on this thread.

EvGeStevenC 07-01-2006 00:54

Re: Hinged Bumper Design?
 
Ian I am going to hurt you I came up with the string idea theo just tied the knots -.-

Tim Delles 08-01-2006 00:06

Re: Hinged Bumper Design?
 
Yeah i have a few now that i have had time to look this over and actually think about it.

1.) How did the bumper system work at higher speeds. Did it result in the robot being forced up or did it not really have any effect?

2.) How much did they extend from the robot when in the lowered position?

3.) And lastly, do you have any drawings of it or and pictures of it?

Thanks

Ianworld 09-01-2006 17:40

Re: Hinged Bumper Design?
 
1 Attachment(s)
Tim, to answer your questions:

1. The bumpers worked just the same at higher speeds, although I suppose super high speeds might have knocked the bumpers out of the way before the robot pushed up agains the robot. The reason for this was due to the torsion springs we attached to the 4 bar linkages.

2. They extended a good 2 to 3 inches out. You can change this, but if you're thinking like my team its going to be hard to fit the bumpers FIRST is allowing the teams in with this system.

3. I do have some drawings, not many on me. I'm attaching that is a side view of the magic bumpers, showing the linkages. I've been told its slightly confusing but its the only thing I have on me right now.

Alan Anderson 10-01-2006 10:38

Re: Hinged Bumper Design?
 
It looks like this bumper scheme is incompatible with the designated bumper design in the 2006 manual. If the optional bumpers are used, they must be of the specified design, and they must remain between in the region between 2 1/2 and 8 1/2 inches from the floor. They are five inches tall. Having them react upwards when hit would violate the bumper zone height requirement.

These hinged bumpers are still usable as an integral part of the robot, but the robot wouldn't get the 15 pound "bonus" weight.

insub2 11-01-2006 21:43

Re: Hinged Bumper Design?
 
would those bumpers violate rule R04????
Quote:

<R04> "Wedge” robots are not allowed. Robots must be designed so that interaction with other robots results in
pushing rather than tipping or lifting. Neither offensive nor defensive wedges are allowed. All parts of a
robot between 0 and 8.5 inches from the ground (the top of the bumper zone – see Rule <R35>) that might
push against another robot must be within 10 degrees of vertical. Devices deployed outside the robot's
footprint should be designed to avoid wedging. If a mechanism or an appendage (a ball harvester, for
example) becomes a wedge that interferes with other robots, penalties, disabling, or disqualification can occur
depending on the severity of the infraction.

Cluskum35 11-01-2006 23:36

Re: Hinged Bumper Design?
 
Quote:

Originally Posted by insub2
would those bumpers violate rule R04????

Whoo! First post. I was one of the 694 subgroup who worked on the bumpers last year. I can tell you a few things:

1. No, our "magic bumper" design would not violate that rule. It's possible to construct them in such a way that they satisfy all of the rules and still slide up and down. You could have them only slide up and down one inch and only stick out 3.5. Of course, building them within those parameters would prove rather pointless. Especially with that slippery fabric on top of them. I think that by allowing some slack for bumpers, FIRST is just saying, "expect a bloodbath. Now here's some padding so your motors don't get too rattled."

2. You could still construct excellent sliding bumpers, if you want that traction advantage. As long as they're not external, you can forego that 15 lb. bonus and make regular magic bumpers that go out and up and down as much as fits your fancy. You can even attach something super sticky that catches on that slippery fabric. The problem there, however, is, again, that you're expecting a bloodbath. Let's say someone bumps into you and one of the sliding hinges gets deformed. Even a slight deformation caused our hinges to become completely stiff last year. In short, anything ornamental is sure to get knocked off.

I'd just stick with the manual. I remember reading somewhere, "don't lawyer the rule. It's there to help." That said, magic bumpers are still the coolest things on the planet. I have mine hanging on my wall.

Alan Anderson 12-01-2006 10:44

Re: Hinged Bumper Design?
 
Quote:

Originally Posted by <R04>
"Wedge” robots are not allowed. Robots must be designed so that interaction with other robots results in pushing rather than tipping or lifting...

Oh, darn. No lifting. That rather clearly rules out the fancy lifting bumpers, I'm afraid.

Rick TYler 12-01-2006 13:51

Re: Hinged Bumper Design?
 
Quote:

Originally Posted by Ianworld
Instead we used an ingenious knot dreamed up by a former girl scout on our team. At the start of the match, another mechanism on our robot would pull out the knots dropping the bumpers into position. It weighed nothing saving us the 3-4 pounds that the pneumatic and its parts added to the bot. The knot however had its own issues: hard to tie a complicated knot

You should have talked to a sailor or a Boy Scout :). The correct knot for temporarily securing a FIRST robotics bumper is the mooring hitch, which is very simple to tie. Just thought you would all like to know... :)


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