[tim-tim]

Originally Posted by Orion.DeYoe

What techniques do you use to keep weight out of your design?

Through the course of time we have learned that we are really bad at guessing weight and initial capability. We used to hold different groups to a firm weight (w/little wiggle room). Over the past few seasons we have developed an excel tool that allows us to keep updating our estimates and eventually compare to our measured weight of the robot. There are two screenshots attached of the tool.

What high-weight situations do you avoid?

I don't know of any 'high-weight' situations we avoid. We like to iterate through CAD. We will spend time to develop a [hopefully] better solution that maintains same baseline functionality, less weight, easier to maintain. Always look for COTS solutions, if nothing else it allows you to compare ideas and draw inspiration.

Bellypans are another area to save some weight or resources. We choose not to use our sponsors for bellypans. We feel their time is better spent making aluminum lightweight in other places. A good piece of birch has served us well over recent years - lightweight, easy to machine, isolation, rigid, cheap, etc.

Plastic (Lexan/polycarbonate) is heavy.

What materials do you use to get the strength you need without putting your robot overweight.

We use a lot of aluminum... but the alloy and thickness tend to vary with the design intent/use. We hardly ever design anything on the robot for more than .090" thk. This year our chassis was .090", which turned out to be more than we really needed; but the game was rough, so it was worth the weight. Most of our mechanisms will be .063" thk. I would say that 97% of our parts are 5052-H32 or 34 (depends on sponsor). This alloy allows for tighter bends and an overall more compact design. When needed we will step up to 6061-T6 or 2024-T3. Sometimes flat pieces are cut from 6061-T6 anyway because that is the typical material from one sponsor. We don't weld much, so that doesn't play much of a role in material selection.

is having an overweight robot a problem you face regularly? Or are you able to keep everything under 120 pounds from the beginning?

We had an issue with weight in 2012 - it got out of control real fast and led to the creation of the excel tool. Other than that, we try to develop our own weight limit as a team - it may or may not be the weight limit listed in the rules. The new approach we use is that each team provides updates on weight on a regular basis, if we are over or getting close to the our team's limit we will discuss and adjust (weight limit is not fixed as long as under 120lbs).

I have heard some teams use phrases similar to: "We are given 120lbs limit. If the robot only weighs 115lbs, then you left out 5lbs of engineering."

At the end of the day, find what works for your team. Every group will be different, and have access to different resources.