Quote:
Originally Posted by PaulYavarow
How do other teams keep your robots under the weight limit? No matter what we do, we here at 1768 always end up just on the edge of the weight limit. Is there something we're missing here? We just drill holes into things and make as much we can from ABS to cut weight from the robot, but that can only go so far.
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Paul,
As mentioned, doing this from the beginning is key; but not always easy. Take some time beofre the season starts to develop a weight strategy. We typically design to 110lbs which leaves 10lbs for error/expansion/unforeseen issues/etc.
Definitely start weighing stuff from the beginning. As you mock up mechanisms for the game get weights for items that will be used on the real robot (transmissions, motors, electronics, etc.). Then develop an [educated] estimate of what the final design will weigh. Keep track of the estimated weights, for comparison purposes to the actual weights when built.
This takes a lot of discipline though. Weekly weigh ins are good, but take it up a notch. Note what was included in the weigh in, and compare to what the estimated weight for what was weighed. This wil not only give you a current weight, but indicate whether you are over, under, on weight 'budget'.
Something else to consider is the design intent of each part. Not all parts need to be 1/8" with 1/4"-20 bolts (just an example). Look at the purpose of the part and evaluate what strength it will actually need. For example, we are using 0.032" (1/32") aluminum in some areas on our robot this year that have low amounts of stress. This will come with experience.
A short list of things to do is know what weight you can't get rid of; meaning know the weight of the drive motors, cRIO (and other electronics), chassis, wheels, etc. We had a barebones driving platform weighing in around 35-40lbs this year (sorry I don't have the exact figure). This means we only had ~80lbs to 'play the game'. Realize that this 40lbs for drive is very hard to lighten due to the amount of required components; so your weight reduction will likely have to come elsewhere.
Some things to do to lighten the robot:
- Remove any unnecessary material - remove corners that aren't supporting weight/components
- Replace 1/4"-20 steel nuts, bolts, and washers with aluminum ones in non-critical applications - aluminum is about 1/3 the wight of steel
- Assemble with rivets where possible - remove bolts and add additional holes for 1/8", 5/32", or 3/16" rivets. Be sure to get the proper grip length. Again, use aluminum in most applications.
- Iterate design - develop a lighter mechanism that has no loss in performance, in fact there should be an increase in performance, that can be added during competition
If you can provide additional info, I would be glad to offer some suggestions for this year (if needed).