Tips on loosing weight (Not spam)

[Ninja_Bait]

Design it to be underweight. That's why they give us CAD!

[kramarczyk]

Ike put together a nice paper on robot weight reductions. http://www.chiefdelphi.com/media/papers/2220

[PhantomPhyxer]

Start off by weighing all parts and recording that weight in an Excel Spread Sheet.
For those parts that are designed in Cad set the the material density correctly and CAD will calulate the part. Insert that number in the Excel Spread Sheet. Where possible use Aluminum. Limit the number of bolts to what you actually need to prevent rotation or shear. If you have to drill holes to mount something then use those mounting holes to mount something else if possible. That will reduce the number of bolts. If you keep track of weight only in CAD then use lump masses for those things like electrical.

The weight spread sheet can also be used for cost of your Robot because you have to account for every part on the Robot.

Fortunatily programming code does not weigh any thing! (:-)

[JamesCH95]

I have the mindset of making everything as light as possible before adding it to the robot. "Pounds are made of ounces" is one of my favorite mantras from building race cars that I have brought to robotics. That is, we try to lighten every part before it goes on the robot. The savings seem trivial at first, but they add up to be significant.

Some tricks:
-welding the kit frame saves ~3lbs of fasteners and blocks and eliminates loosening frame fasteners from your pit checklist
-plastic bearings are super-light and can replace metallic bearings in some applications
-using 25 series chain instead of 35 series chain drops a significant amount of weight, I would not consider this on the drivetrain except as a last resort though
-designing with an eye to keep wiring runs as short as possible not only reduces weight, but improves electrical system efficiency (consider making that beautiful wiring run a little more utilitarian)
-the new air compressor is around 2.6lbs lighter than the older compressor, that's huge (FWIW I aim to use pneumatics for at least 3 small functions or 2 big functions to consider them worth the weight)
-using high-grade fasteners can drop weight if they are selected properly
-consider eliminating redundant fasteners
-consider replacing low-load fasteners with zip-ties, plastic bolts, or velcro
-speed controlling through software rather than excessive gearing where possible, one encoder weighs a lot less than another sprocket and chain set or pair of gears

There is very rarely a weight-reducing trick that saves a huge amount of weight. In my opinion good light-weighting is accomplished through a systemic discipline of cutting ounces, or fractions of ounces, wherever possible.

[Gdeaver]

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.

[IKE]

Using thinner materials is the most frequent weight reduction I see. Often teams will use 1/8" plate where 1/16" will do (be it plastics, aluminum, or whatever...).

This is especially true wih Body panels. I frequently will see teams with large 1/8" body panels. Often 1/16" or even 0.030" thick polycarb will work just as well. In fact the 0.030" polycarb and access to a vinyl cutter make your robot looks classy, and add protection for very little weight.

When working with sheet-metal, use "shape" to add stiffness, not thickness. Adding in flanges can often increase the stiffness of a panel with very little (+10-20%) additional weight. Adding thickness will often do very little (compared to flanges), and increases the weight proportionally. Adding thickness and then removing material via a CNC, looks cool, and functionally may work well, but does require a fair amount of work or tooling.

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The pneuaire.com accumulators are a great way to reduce weight and add air volume. I saw a bunch of these on 1503 last year and got the manufacturer from them. We used several on our robot, and i had a whole bunch of spares that we donated to another team that had around 10 metal accumulators on their machine.

Be careful with aluminum gears. When done right, there are some significant weight savings opportunities, but know that is is difficult to do them right. Aluminum has several properties that are quite poor for gears. Many gear experts would recommend to NEVER use aluminum. I do think they have their place, but you should be extremely careful and really need to know what you are doing.
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Beware of the attitude that "its too late to replace...". I have heard teams say this before, only to remove functional mechanisms at competition in order to make weight.

[Chris is me]

Originally Posted by IKE

Be careful with aluminum gears. When done right, there are some significant weight savings opportunities, but know that is is difficult to do them right. Aluminum has several properties that are quite poor for gears. Many gear experts would recommend to NEVER use aluminum. I do think they have their place, but you should be extremely careful and really need to know what you are doing.

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.

Originally Posted by Gdeaver

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.

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.

[IKE]

Originally Posted by Chris is me

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.
.

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.

[EricH]

Originally Posted by IKE

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.

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.

[ratdude747]

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.

[Jon Stratis]

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

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.

[Al Skierkiewicz]

Originally Posted by eagle33199

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

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

[JamesCH95]

Originally Posted by Chris is me

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.

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.

[ThunderTrain]

We weigh everything every time we change something. this way we can keep track of weight and get our workout in.

[Ninja_Bait]

Originally Posted by Chris is me

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.

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.

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.

Originally Posted by eagle33199

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

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

Originally Posted by PhantomPhyxer

Fortunatily programming code does not weigh any thing! (:-)

Our code extends past the bumper perimeter sometimes.