Tips on loosing weight (Not spam)

[ajlapp]

Team RUSH hasn't used pneumatics in their robots since 2004 and this has been a tremendous weight saver in my opinion.

Initially we stopped using them because we thought the package available at the time was too heavy for the utility you achieved. We would often have one or two systems that were candidates for pneumatics....this didn't justify adding the ~8 lbs. needed for the compressor, tanks, hose etc, etc. Of course we discussed eliminating the compressor for some designs, but in the end we just eliminated the whole system.

Originally I hated that we didn't have access to pneumatics...each year I would lobby for it. Now that I recently started helping a new team, I find myself lobbying them to eliminate it to save complexity and weight.

Of course a lot of teams are able to integrate all motors and a complete air system while staying in weight, but it's a very liberating feeling heading to scales with 8-10 lbs. to spare.

Now that the systems have become more open and lighter I'm sure we'll take a serious look at going back.

[amoose136]

Would any team care to post a past weight budget? I'm curious to see the average weight composition of the FRC robot.

[artdutra04]

Design everything ahead of time in CAD. If you set the materials appropriately, you can get an accurate estimate of your final robot weight. The more detail stuff you model, the more accurate the weight estimate will be. Changing designs in CAD to reduce weight is much easier, cheaper, and more effective than having to drill hundreds (potentially thousands) of holes in your mechanisms after they're already assembled.

[s_forbes]

Originally Posted by artdutra04

Design everything ahead of time in CAD...

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.

[Wayne Doenges]

One word...Monocoque
No internal frame.

[ratdude747]

Originally Posted by Wayne Doenges

One word...Monocoque
No internal frame.

sounds like most cars anymore... unibody anybody?

[JamesCH95]

Originally Posted by s_forbes

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.

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.

[Marc S.]

I don't know much about how you build your robots but making everything in 1/16 wall tubing instead of 1/8 will save a lot of weight and time(if you pocket 1/8). It is also stronger than pocketed 1/8 wall tubing. You can save a lot also if you use aluminum rivets instead of bolts whenever possible.Smaller wheels and custom gearboxes can save weight if done correctly(if you are unsuccessful in designing your own just copy our 2010/2011 gearboxes/drivetrain(link below)).

[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.