Methods of adding ballast to underweight robots

[vivek16]

I'd like to start this discussion up again. We are underweight but also have skewed weights over each wheel. I've been thinking of riveting 2 foot long pieces of 1x1 (sealed on one side and removable cap on the other) to each corner "tier" (vertical beam on the bot that essentially form a box) and filling them with steel or lead shot. This way, we can quickly add more or less shot to each beam on thursday to adjust weight with each wheel resting on a cheapo bathroom scale.

Any thoughts?

thanks, Vivek

EDIT: What sort of store would have lead or steel shot locally? I know Mcmaster has it but shipping will be ridiculous.

[gorrilla]

dimond-plate is obviously the best choice

[Bob Steele]

Originally Posted by vivek16

EDIT: What sort of store would have lead or steel shot locally? I know Mcmaster has it but shipping will be ridiculous.

Try a local gun store. They should have lead shot in sacks for use by shotshell reloaders. They will have several different sizes...your choice.
Not cheap but you won't have to ship it..

[vivek16]

To err on the safe side, I should have some ideas on alternatives to lead shot.

I just got the idea to use pennies instead. They are cheap and easier to use.

With 2.5 grams per penny, 20 pounds of pennies costs about 36 dollars which isn't too bad.

-Vivek

[Bob Steele]

I think you could use pennies ... They are just about 25% less dense than lead so that's not bad. Better than steel which is something like 30% less than steel
Steel bolts are cheap though...put them or pennies in a PVC pipe...

tungsten is what you really want... but expensive...twice as dense as copper..
pretty cool stuff...

R

[vivek16]

Turns out newer (past mid 1980's) pennies are actually 97.5 percent zinc and only have a 2.5 percent copper coating. Who knew?

I think either the pennies or just scrap bolts we have lying around will work. I'll have to take a look at our junk bins later this week.

-vivek

[Mike Betts]

Originally Posted by vivek16

... What sort of store would have lead or steel shot locally? I know Mcmaster has it but shipping will be ridiculous.

Any sporting goods store (and most Walmarts) sell steel BB shots for air rifles. That being said, I'd use pennies as noted by others...

If you go the "shot" route, please be sure that the "removable cap" you use is very secure. In the event that your robot tips over, pounds of "shot" spilling onto the floor will cause a very dangerous situation for referees, field reset, et cetera and will almost certainly get you disqualified...

Regards,

Mike

[IndySam]

To add to Al's pneumatic suggestions, the brass fittings can be screwed together and can add a lot of weight fast.

[Al Skierkiewicz]

It will be interesting to see teams using pennies and listing them on the BOM.
Ex. 2000 copper or copper/zinc one cent US or Canadian coins Undepreciated Cost $20.00

[Dick Linn]

If you can find a gunshop that will loan you a bag of Tungsten shot, that is about as dense a material as you'll commonly find. Costs about $30./lb. Lead shot is much cheaper. An old bicycle inner tube partially filled with shot or old wheel weights and tied up like link sausage should be pretty easy to strap on there somewhere.

[DonRotolo]

We found (and used) a 1" square bar of bronze which weighs 0.17 pounds per inch. Last year we used about 8 pounds of it, this year about half that.

large copper wire - like 600 MCM - is heavy and relatively inexpensive. We have an 8 inch piece which weighs about half a pound, maybe more. If you know an electrician, maybe she will loan you a few feet - but give it back after the season, or pay the scrap value to them at least.

I hear small pieces of railroad track are heavy...

[MikeMascaro]

We're using pieces of steel we had laying around as "armor plating"

[Teammax]

Originally Posted by Don Rotolo

We found (and used) a 1" square bar of bronze which weighs 0.17 pounds per inch. Last year we used about 8 pounds of it, this year about half that.

large copper wire - like 600 MCM - is heavy and relatively inexpensive. We have an 8 inch piece which weighs about half a pound, maybe more. If you know an electrician, maybe she will loan you a few feet - but give it back after the season, or pay the scrap value to them at least.

I hear small pieces of railroad track are heavy...

Don has the same idea we did. We used 1" diameter brass rod because it is what we had around. It looks very sharp when polished up and was easy to mount pretty much anywhere we wanted. One rod runs along the back of our base and weighs about 10lbs. The other rod runs near the front and weighs about 8 lbs. In the end I would recommend this method for adding weight due to the ease of mounting and the nice look it adds.

[Jeff Pahl]

Originally Posted by Mike Betts

If you go the "shot" route, please be sure that the "removable cap" you use is very secure. In the event that your robot tips over, pounds of "shot" spilling onto the floor will cause a very dangerous situation for referees, field reset, et cetera and will almost certainly get you disqualified...

We had this happen a few years ago at Peachtree. I think it was 2005. A team used a large container of BBs to add ballast. It ruptured. We spent the rest of the weekend picking them up Spilling a bunch of shot on the floor at the inspection station while adding it to your robot will not make you real popular, either.

Make absolutely sure that any container of shot is durable, secure, and sealed. I can promise you that any robot at 10,000 Lakes using shot for ballast will invite extra attention at inspection.

The best method I have seen so far this year for adjusting weight at the scale is to add some pieces of threaded rod to the robot, and bring a bucket of washers that fit over them. Add washers to the desired weight, and then put the nut on the rod. Use big rod, like 1", and the washers will also be big and substantial weight. If you are way under weight, bolt on some of the heavy stuff mentioned earlier in this thread to get you close. I've always been partial to barbell plates.

And the best thing I have heard of so far this year for ballast is an arbor press, borrowed from another team in the pits...

[Creator Mat]

What my team does is we take weights out of a weighted ankle band (just ask for one at sports authority or D(stupid censor)icks they will find it for you) and just drill holes in them and zip tie them somewhere safe. Its great because they come in 1 lbs increments so you can add just enough.