Weight

[Mike Martus]

There are several important concerns that have been brought up here.

1. The 130 weight is a design constraint, part of the challenge.
2. Safety - 130 divided by two persons 65 each that is still a lot of weight if you fall or have a distance to go. A Major safety concern.
3. Next year I believe that the battery will not be included in the weight and there may be a gain if say FIRST decides that 120 lbs is the weight without the battery. A net gain of about 4 pounds or more.

No matter what the limit is set at, I believe that there will always be the "pushing of the limit" to build the best durable machine.

Teams that are consistently designing and end up with weight problems need to look at their design process and make corrections in "Weight Management".

[Swampdude]

For some strange reason we've never built a robot more than 135 pounds (prior to seriously considering weight reduction). Usually the kit material puts you in a standard range for extra robot material to wind up around 130-135 pounds, it's some kind of natural law. Anyhow, I have faithfully thrown my back out every year carrying these things on and off playing fields. But I still would like to see it go to 135. It has been our magic number.
This year we were really on the ball with weight reduction in the design (120 lbs) but, at the comps we had to beef her up to take the punishment everyone was dishing out, and wound up 131 minus shavings to 129.999.
The thing is, years past without trying too hard we got around 135, then this year we went overboard and got 120. It's not a big difference. Experience has taught me how to do a lot with 5 lbs - true. But inexperience and 5 extra pounds would make making robots (which is extremely stressful) much easier.
It would be good to see a weight study showing what the kit material puts you at for a typical bot configuration. Then see what kind of weight/mass ratio is left over. I bet it's not much.

[ChrisH]

Originally Posted by Mike Martus

There are several important concerns that have been brought up here.

1. The 130 weight is a design constraint, part of the challenge.
2. Safety - 130 divided by two persons 65 each that is still a lot of weight if you fall or have a distance to go. A Major safety concern.
3. Next year I believe that the battery will not be included in the weight and there may be a gain if say FIRST decides that 120 lbs is the weight without the battery. A net gain of about 4 pounds or more.

No matter what the limit is set at, I believe that there will always be the "pushing of the limit" to build the best durable machine.

Teams that are consistently designing and end up with weight problems need to look at their design process and make corrections in "Weight Management".

Some tips for Weight Management

1) "budget" no more than 90% of the weight limit. ie if the limit is 130 lbs then the total estimated weight of all systems should be no more than 117 lbs.

2) Identify and quantify non-negotiable weight first. So know how much your controller, breakers, lights etc. weigh. Subtract this weight from the budget.

3) what is left is available for adding non-essential systems. Note: depending on the game, a drive system may be negotiable.

4) Assign budgets for all subsystems based on criticality. A really critical system should have a bigger budget than a nice-to have.

5) Do a weight estimate for any proposed subsystem BEFORE you build it. Hint we've found that Inventor is pretty good at weight estimates if you put in the correct material data.

6) Use your estimates to trade off between systems.

7) Resist the temptation to say "I think I can get a couple of pounds out" and then use the lower number. Every item in your estimate should have documentation to back it up. If you think you can take weight out, fine. Prove it first, then change the number.

8) Track the weight of each subsystem continually. If possible weigh each part before it goes onto the robot.

9) Use a spreadsheet for your weight tracking. Constantly compare actual vs estimated weight. Beat on the designers of subsystems that are over weight to get the weight out. The spreadsheet can also be used to identify "heavy hitters". Items that are extraordinarily heavy (and thus prime targets for speed holes) or items that use a lot of weight for minimal functionality.

10) Assign a single person whose whole job is to make sure you meet weight. We call ours the "weight czar" a term that comes straight out of the aircraft biz. In fact, at the "bird factory" I work in, every program has a whole department dedicated to tracking the current estimated and actual weight of the aircraft. We wouldn't do that if we didn't think it was important, there too many other things we need to throw bodies at to waste them on something unimportant.

11) Remember that nothing ever gets done within the budget. That's why you only allowed 90% at the beginning, to account for unknowns and overruns. If that doesn't work this year, then next year cut the budget to 85%

[Stu Bloom]

Originally Posted by ChrisH

Some tips for Weight Management

...at the "bird factory" I work in, every program has a whole department dedicated to tracking the current estimated and actual weight of the aircraft. We wouldn't do that if we didn't think it was important, there too many other things we need to throw bodies at to waste them on something unimportant ...

Chris is ABSOLUTELY correct. Regardless of what the numerical limit is, it would benefit us all to use these weight management ideas.

Here at Rolls Royce we also have several people dedicated to tracking the weight of our engines. Any change that is proposed for any flight engine is heavily scrutinized for weight impact. We pay a hefty financial penalty if our engines exceed contractual weight limits.

[Matt Adams]

Originally Posted by Mike Martus

3. Next year I believe that the battery will not be included in the weight and there may be a gain if say FIRST decides that 120 lbs is the weight without the battery. A net gain of about 4 pounds or more.

Congrats on an accurate FIRST prediction!

Matt