While in the computer lab at midnight last night, thinking about how much weight fasteners will add to our robot, I figured it might be a good resource for some teams if we made a sort of “Weight reduction - How to do it” thread.
So if your in the mood to share, feel free to tell us all how you make your robot lighter. Anything from the smallest task of say, making your spacers have as thin a wall as possible, up to say, removing an arm.
I’ve said it before:
This was already discussed here: http://www.chiefdelphi.com/forums/showthread.php?t=44155
Replacing steel bolts with aluminum versions. Very light and still strong enough for most purposes.
1618 hasn’t gotten into the weight-reduction business (their past two robots have been far underweight, and this year’s is still obviously in the pipeline), but I do remember a few tricks from 1293:
-Switching out our 1/8" aluminum hopper for a thinner stainless one
-Hacking off most of our tower (not because we were overweight, but because the weight was high up)
-Gratuitous use of the slugbuster (a hydraulic device for poking large circular holes in sheetmetal)
-Cutting the team numbers into our covers, causing us to lose weight for a required feature rather than gain it
-Rivets, rivets, and more rivets (and rivet nuts for places we needed to get in and out of)
-Running as short a wire as we could safely use (something I’m sure Al Skierkiewicz is happy to see as well)
-Thin-walled metal spacers on our Kitbot axles
-Going from six polycord runs on our ball pickup to four (and ultimately zero with the top getting chopped, but that’s a whole other ball of wax)
-Plastic belt pulleys instead of metal
-Plain paper and Velcro for attaching school and sponsor information. (It works, I swear!)
Replace Aluminum bolts with Nylon ones.
Even better for some applications.
You don’t really need a steel or aluminum bolt holding down the RC now do you?
Use 2 screws on muffin fans instead of all 4 corners.
TRIM THOSE WIRES!!! You don’t need 1’ of cable going from your battery to your quick connect if the battery is right next to the breaker.
ONLY SWISS CHEESE THE BOT IN WEEK 6!!!
None of this “speed holes in week 1” nonsense!!!
You can’t put material back as easily as you can remove it if you need to mount anything, even something as simple as a potentiometer, limit switch, or a sensor of some kind.
Rivets, we were able to take almost 5 pounds of bolts off our robot last year by replacing them with rivets. Also choose your materials wisely, sheet metal is your friend, too much extruded aluminum is not. Even if you are not at the cheesing stage yet with your build, plan our where you can reduce weight if you have to, and expect to have to take apart your robot a couple of times throughout the season (keep welding till you know your weight).
Corrugated lexan (green house material) instead of lexan for side shields, and coverings…
Heres a fun story from the Nu-Tron from around 4-5 years ago:
They brought the bot up to inspection and placed it on the scale. The scale read 130.0…130.1…130.0…130.1 (for all you youngens back in the day the limit was 130 pounds WITH a battery). Eventually the scale stopped at 130.1. One of the team members decided to check the air tanks, they were full so he released all the air pressure…the scale dropped to 130.0 and they were good to go. Moral of the story: EMPTY YOUR AIR TANKS!
This year Team 1323 was able to cut 11 lbs of our basic chassis by welding our frame together it was a task our team was shooting for since the end of last year when we invested in a tig welder.
We’ve used some fairly large bolts in the past to mount various mechanisms, wheels, etc… A 1/2" bolt is typically overkill in terms of strength, but the diameter has been our requirement. So, we’ve actually drilled out the center of our larger bolts in order to reduce the weight of this large hardware, and it definitely works.
YMMV, good luck.
We have a saying that we use over and over when looking for weight reduction;
Steel parts first, then alluminum, then plastic.
Cutting/drilling holes in a 1/8" lexan side plate for instance is pretty inaffectual. On the other hand, putting a gear or sprocket in a lath and taking some “meat” off it can pay big dividends.
Our team is working hard to actually predict weight of the final design in order to avoid the problem we had last year. Every piece is being designed with speedholes included, so hopefully when it all goes together it will be underwieght.
In case anything is heavy and still has room for holes at the end of the build, we have a Rotex punch which can be used to speed up the cheesing process.
Well one of our experiences last year was that we were 12oz overweight at tech for the regional. This was already AFTER drilling and trimming the snot out of the robot before we shipped.
So one of the engineering mentors goes around the robot with 2 of the students and tells them which bolts, nuts and washers to remove. After about a 1/2 hour he stood there with 2 hands FULL of “extraneous, unnecessary hardware” that weighed…you guessed it - 3/4 of a pound. Much of it came fro the KOP frame joints where 1 fastener was just fine due to our design last year.
Assign a couple of team members to monitor the weight of everything you put on a robot. It will help you during week 6. Remember, everything weighs something (even paint).
This year it already looks like we are having weight issues so we have been taking the weight of EVERYTHING (components, motors, spikes) and adding them into an excel file. Then for things that arn’t built yet like the chassis, wheels and stuff we have done extrememly acurate Solidwork models of them and these give us the weight.
#1 tip to avoid overweight issues:
Plan/design everything first then build. dont design as you go.
weight relieve every sprocket, pulley, gear, and gear box that you can. weight relieve all aluminium and lexan plates. These are some of the densest things on most people`s bots. also, make sure you are using gears belts or chain that is appropriate (not overkill), as jumping up to the next strongest category can mean doubling the weight of these components.
Another thing to keep in mind;
If the component that you designed is still strong enough after you have drille the cheese out of it, it is possible that you could have just used thinner material to start with.
Our robot last year was allmost all pollycarbonate. We were more than 40 pounds overweight. We spent week 5 and thursday of our first competion drilling the holes in the frame larger, trimming corners off of pieces and many speed holes. 3 in hole saw works well but this year we have acess to even larger ones. My advice - allways keep weight into consideration.
Adding some fiber to your robot can work wonders for weight.
Just as a funny story although it wasn’t funny then. When i was with a now defunct team we had an engineer who insisted we had to use 1/4 in thick aluminum for our sides. This was several years ago when you could only weight 130 with your battery. I told him many times it wasn’t necessary to go with something so heavy. He still insisted. When we finished the robot we weighed it and came in at a whooping (are you sitting down!!) 217 lbs:ahh: . What could I say other then I told you so which of course I didn’t. Shaking my head and handing out the sawzalls we made it down finally to 130 on the dot. It only took us 9 days of making swiss cheese out of EVERYTHING. Needless to say that engineer was never seen nor heard from again.