weight advice

we desperately need to cut down some weight, does anyone know any tricks to do so (besides drilling speed holes)

[Chris Hibner]

Originally posted by SharkBite
we desperately need to cut down some weight, does anyone know any tricks to do so (besides drilling speed holes)

The trick is to do some math.

We had to lose a lot of weight last year. We tried to do it as systematically as possible and it worked very well. You really need to find the densities of the materials you are using and do some calculations.

An easy way to get started isto determine the weight of a 1" long piece of the most common materials on your robot. For instance, you can say that each inch of aluminum tube is X lb, each inch of steel bar is Y lb, and each inch of 1x1 8020 is Z lb, etc. This will give you an immediate idea of what you're up against and allows you to determine roughly how much material you need to remove to lose the necessary weight. It also gives you an idea of how much "bang for the buck" you get by removing one thing vs. another.

Usually, you won't be able to get rid of an aluminum bar because it is supporting something. Then you need to think to yourself, what if we cut it in half lengthwise and make it an aluminum channel? Will it still work? If so, calculate how much weight you save. We were able to turn enough square tubes into channels last year to save about 5 lb. We didn't turn the entire tube into a channel (we left the ends square for mounting reasons), but we made the middle section a channel.

Also, holes are very inefficient for removing weight. You can do much better in terms of weight loss with little reduction in strength by making slots or pockets instead of holes. For instance, if you are planning on doing holes, run a mill between every other hole to make a slot or pocket. If the member doesn't carry a lot of load, connect three or four holes in a row. You'll be amazed at how much more weight you remove by doing this rather than by simply doing holes.

Another HUGE saving comes from sprockets, pulleys, and gears. You can usually remove about 1/2 to 3/4 of the material in a sprocket, gear, or pulley if you do it properly. If we left the gears and pulleys on our robot for this year the way the came off-the-shelf, our robot would be about 5 lbs heavier.

There's no reason to use a solid steel gear like they come. Take off a good portion of the hub. Mill spokes from the hub to the gear face instead of leaving it solid. Also, if the face of the gear is 1/2 inch, there is no reason that the material from the hub to the face has to be 1/2 inch - usually you can thin this out significantly (just remember to leave the face at the necessary thickness).

I hope this helps. The most important thing is to do some calculations and have a plan before you start to reduce weight. We lost a total of 15 lb last year without losting any functionality or robustness. We made sure we had a good plan and did some math first. It worked really well.

[Wetzel]

Drill more holes!
It also depends on how much you need to lose. An ounce here and an ounce there will make a diffrence, even if you need to lose 10 lbs. How much do you need to lose?

thank you so much, we had figured out the material parts and the math and such... but your advice about extra gears and pulleys is gold.... didnt think of that

[Anton Abaya]

also, consider getting rid of a mechanism at last resort.

sometimes removing a drive wheel and replacing it with casters is also a solution.

-anton

ps. you can always drill holes in your battery (j/k)

that is absolutely the last resort though....... our drive train doesnt allow for that as of now

[Elgin Clock]

On our robot(s) we have changed a brass bushing into a Delrin one, We have also "Swiss Cheesed" the <edit>ROBOT</edit>!

It all depends on how much weight you need to lose as well.


We are going with the slotted idea to reduce weight on our side panels, instead of a bunch of holes.


NOTE:

MAKE SURE YOU FINISH DESIGNING YOUR ROBOT BEFORE REMOVING MATERIAL!!!

Last year we jumped the gun on machining holes and accidentally machined a spot where a future mechanism sat. We had to weld a panel in the spot we machined, Not a fun thing to do!

[Chris Hibner]

I forgot another thing: Lexan (and other plastics).

Wherever possible, substitute Lexan instead of aluminum. This is advisable only when the part you're substituting doesn't carry much load (if it carries a lot of load, you'll need to do some calculations to see if it will survive and not bend too much). For instance, all of our control system parts last year were mounted on an aluminum plate. We replaced the aluminum with Lexan and saved about 2 lb. The heat conduction properties of aluminum was nice, but the matches only last 2 minutes so it's not that necessary. You may need to reinforce the Lexan with a couple of thin aluminum strips to keep it from sagging too much, but overall, you can save a lot of weight.

Also, a lot of bearings can actually be replaced with delrin bushings. I would keep the bearings in your drive wheels, or other areas that cary an enormous amout of load, but delrin bushings are adequate for most spinning shafts that don't carry a lot of loading.

Just remember that you don't need to design your robot for infinite life. As long as it lasts a few months, it will be fine.

[Mike Norton]

To get rid of wieght. First don't build something that will have alot of wieght


Everything you put on the robot have someone look at it and see if there is another way of doing it lighter.

We used it put holes in our robot many years ago. But now we make sure what we put on the robot is the best wieght we can come up with.

we run with track. within 3 years we took out 10lbs just in the track system. this is because we figure a life span of a 1000 hours. after that we have to go in and start changing things.

if you give us more information about how your robot looks or going to run I bet we could help you out alot more.

[CaptainPlaid]

Depending on how bad the weight problem is you can get very creative. For example, if you have a 1/4-20 bolt there is wasted weight on the very inside of the bolt. DRILL IT OUT! "Hollow bolts" take a while to make but can really save some unexpected weight if you are desperate.

you guys have come up with some great stuff, but unfortunately we are stuck drilling holes

you see, we tend to have an overweight robot every year and have to cut it dont last minute due to simple deseigns that end up being eleborate (i know you guys know what i mean on that one) we end up building everything out of the lightest material possible from the beginning and thats why we are in such a crunch now, even drilling holes (pockets slots included) may not remove enough

i wish i could explain the design and see if anyone could help from there, but my team tends to operate under a code of secrecy for the most part (just certain mechanisms) and i wouldnt want to infuriate anyone

i never thought of drilling out bolts though.... its a small area but youre right, it would add up

oh, and i bet this brainstorming about saving weight has helped other people too, so thank you guys

[Dima]

our bot was over weight so we went out and bought titanium bots and nuts and washers etc... 130.0 after that

[nwagers]

I think that some people worry too much about secrecy. At this point in the build, no one is going to change their robot design because your idea is better. This is because there isn't enough time.

Just my thoughts

[Leo M]

"I have one word for you - PLASTICS."

http://www.microplastics.com/

[UCGL_Guy]

Welding your frame or pieces together saves weight and adds strength over bolted systems if you have the means.
KY