Re: Tips on loosing weight (Not spam)
 

Composites can save weight over AL. If I remember correctly, This years arm which was made of pultrutions and polypropylene weighted 65% compared to the same structure in AL. Working with composite require methods that are different than working with metal. Do the research before using them.

Re: Tips on loosing weight (Not spam)
 

Lightening the steel gears, while not particularly FUN to do, isn't very hard and will get you a decent amount of the way there with regards to weight savings.

I'll put in a vote for composites as well. Pultruded fiberglass is very rigid, thick stuff with a low density. Fiberglass tubing is great for something like an arm.

Re: Tips on loosing weight (Not spam)
 

Absolutely, I can't believe I forgot to add "lightening" steel gears. For those that are not familiar, you can either cut pockets with a mill, or undercut the gear between the teeth and the hub on a lathe (this is what we usually do). When doing this, make sure to leave a littl material underneath the root of the gear tooth as this can be a highly stressed location on a gear. Also leave material for the hub as this is either the torque transferring area, or has the bearings on an idler gear. We can often cut about 50% of the weight out of the standard AndyMark gears.

Just be careful how you "cuck up" the gears in a lathe so you do not damage the teeth.

Re: Tips on loosing weight (Not spam)
 

You can do the same thing with sprockets. Just be careful, for the same reasons. A couple of large sprockets have failed catastrophically in competitions after being lightweighted. I remember or remember hearing about two incidents from 2004--in one case, the sprocket turned into a pretzel; in the other, the hub broke free after the season, disabling that particular robot by removing one of its highest-traction wheels from the drivetrain.

Re: Tips on loosing weight (Not spam)
 

One trick to saving weight is to get rid of unnecessary parts.

Another thing i advise teams NOT to do is to use plastic chain where any significant torque is involved... I've seen it bomb catastrophically before... remember that with chain, one weak link ruins the whole loop.

Agreed on using 1/16" where possible...

one last tip is that if you have to resort to cheese-holing, do it to low load things higher up on the robot... having a low center of gravity is key to a stable robot. every little bit helps.

Re: Tips on loosing weight (Not spam)
 

The biggest way to lose weight... Ask the inspector to take his foot off the scale :p

We've never really had a problem with weight on the robot... In fact, most years it's the exact opposite! We always end up either significantly under weight, or spend some time figuring out how/where to add weight (2008 we had a 20lb steel plate bolted to the very bottom of the robot, 2009 we bolted steel plates outside of our cantilevered wheels to support the bumpers, 2010 and 2011 we were under weight - 2011 by quite a bit).

You need to consider weight with everything that goes on the robot - it's easy to "over-engineer" something by building it with bigger/stronger parts than are really needed. What's difficult is building something to be just as strong (and thus heavy) as it needs to be, and no stronger.

Re: Tips on loosing weight (Not spam)
 

Quoting this for truth! Not only do you have the benefit of part masses being calculated quickly, but you also have the ability to alter and optimize the design on the fly. On all of the better robots that I've been a part of designing, weight was never even considered; we spent so much time creating an efficient design that weight didn't need any attention. A good design will by lightweight by nature.

It always amazes me how so much attention is spent on eliminating fractions of a pound in the drivetrain when usually much more can be saved with an efficiently designed manipulator. Remember to design the robot as a whole and not just each part independently.

Re: Tips on loosing weight (Not spam)
 

One word...Monocoque ::safety::
No internal frame.

Re: Tips on loosing weight (Not spam)
 

A thought that occurs when reading this: the drive-train is one of the only truly well-understood systems on an FRC robot (I think) because every year every robot needs a drive train. Repetition and redesign of drivetrains over the seasons characterizes the the required durability/strength/requirements very well. This allows the drive train to be thoroughly analyzed and designed well over years through many smaller design tweaks, as compared to a manipulator or game-specific feature that must be developed, analyzed, and optimized in weeks.

Re: Tips on loosing weight (Not spam)
 

Cmon! Jeff and I only did that to you once! OK maybe twice but that was all I swear!

Re: Tips on loosing weight (Not spam)
 

sounds like most cars anymore... unibody anybody?

Re: Tips on loosing weight (Not spam)
 

We used fiberglass square tubing (1x1x.125) for an arm this year. It bowed under the weight of our claw (though to be honest, the claw had Banebots gearboxes that were 3 stages too large and 35 chain for a while), and we were always afraid that our bolts would rip through the walls. It happened once, but only with 2 countersunk bolts. We immediately put fender washers on all the other ones and we survived Hartford and CMP. I would be wary about using fiberglass again for an arm. While it might be okay for an upright support or something structural, it doesn't have the strength of aluminum, and we definitely spent every match dreading the moment where our arm would shatter and shower our electronics in powder. :ahh:

If we had used aluminum, we'd have been overweight and it'd be too heavy for the motor. But honestly, it wouldn't have given us as many scares as the fiberglass did. I think we got pretty lucky, but there were always close calls. If you want to use composites, don't repeat our mistake and remember that they are not metal, no matter how much they act like it.

Just keep your mentor's foot under the scale; that's what we do.

Our code extends past the bumper perimeter sometimes.

Re: Tips on loosing weight (Not spam)
 

As with anything, overkill can be spectacular:
http://www.carbonfibertubeshop.com/t...roperties.html
http://www.dragonplate.com/ecart/categories.asp?cID=88

But I agree that any composite can be a great way to cut weight.

Re: Tips on loosing weight (Not spam)
 

I've only used stuff in .25 inch wall thickness - much better results that way for rigidity but lightening is recommended.w

Re: Tips on loosing weight (Not spam)
 

The way 1625 did it last year, on accident.

Get a scale thats miscalibrated and you don't know about it, make it read around 10lbs over what the weight actually is.

This may have happened last year....showed up at wisconsin with a robot with 11 motors and 8 cylinders+compressor, at 108lbs.