Lighter Robots

[bardd]

You can use #25 chains instead of #35 (that you get in the KOP). #25 chains are twice as light, and even though they're weaker, you can still hang 6 robots (~720 lbs) on a single chain without it breaking (it can hold up to 780 lbs). Sometimes you might want to use the regular, #35 chains in arms and the like, because of the stress (just to be on the safe side, there's no reason a #25 chain will break on an arm), but there is no reason not to use them in the drive system, unless you don't have the money to buy them.

[John]

One thing to remember about #25 chain is it must be tensioned properly in order to work well, while #35 chain pretty much keeps working even if it has a little slack in it. So if you use it, make sure you have some plan for keeping it tensioned, either with a mechanical tensioner or by designing exact center-to-center dimensions.

[dtengineering]

Originally Posted by AlexH

Tell your robot to lay off the McDonalds...

Why would you want a lighter robot? Heavier robot = more downforce on the wheels = harder to push.

True enough... but often at competitions you have to make repairs and/or upgrades to your machine. As you are doing them under the heat of competition, they rarely make your robot lighter.

In Toronto one year we weighed in at about 118.5, broke a component or two, fixed them up and strengthened them a bit and... then had to be reweighted for elimination rounds.

120.0 lbs.

I'd also suggest building your robot a little under sized in each dimension so that in the event of a major impact causing a slight frame twist (or adding a bolt to make a repair) you don't go from legal to illegal.

As a tech inspector I am always pleased when size and weight are mere formalities and not serious obstacles.

Jason

[AdamHeard]

I could go on for days, but I'll list the few that bring in the biggest weight savings for the least effort for us.

-thinner materials (both tubing wall thickness and plate in generally). Thinner extrusion tubing is far lighter and far more efficient in terms of strength.

-Plastic spacers/standoffs (they're cots from mcmaster in all sorts of sizes from $5-10 for 100 QTY) instead of custom metal.

-Smaller Fasteners. We try to only use #10-32 (which is killer strong if you check the math), and have now implemented #4-40's to supplement them in lower load spots.

-Focus on Quantity. Look at what parts you robot has a LOT of, take a small bit of weight from them (either in thinner material, pocketing, whatever is is) and it adds up fast.

-Plastic fasteners for electronics and low load spots (plastic rivets as well).

-Rivets instead of bolts for many items. We tend to add a lot of little gussets, brackets, doo-dads, wire tie downs, etc... If we bolted all these on versus rivets, it'd add up FAST!

Most of what I suggested above is pretty much effective use of COTS fasteners, and would maybe cost a team $100-200 per season versus their usual methods, but can easily save 5+ lbs without changing the function, strength, or performance of the robot. Pick up 100 1.5" long 1/4-20's with their associated washers and nuts and you'll see what I mean.

[bardd]

Originally Posted by AdamHeard

-Rivets instead of bolts for many items. We tend to add a lot of little gussets, brackets, doo-dads, wire tie downs, etc... If we bolted all these on versus rivets, it'd add up FAST!

Also, if you want to use bolts, try and use the smallest possible. According to stories of the older guys in my team, in 2010 the robot was 0.5lbs overweight three hours before shipping, so they cut all the bolts and left only the length they needed, and that got them to just under 120lbs. Since cutting bolts is not recommended, becuase it makes them alot harder to open and close, you better use small bolts to begin with.

[Ian Curtis]

Originally Posted by bardd

Also, if you want to use bolts, try and use the smallest possible. According to stories of the older guys in my team, in 2010 the robot was 0.5lbs overweight three hours before shipping, so they cut all the bolts and left only the length they needed, and that got them to just under 120lbs. Since cutting bolts is not recommended, becuase it makes them alot harder to open and close, you better use small bolts to begin with.

Thread a nut on before you hacksaw the excess off, then unthread it off afterwards. It may turn off pretty hard, but it will clean the threads up significantly.

Since steel is way denser than aluminum and teams often tend to use much larger bolts that necessary, this is probably the first course of action on Thursday when you try to meet weight.

[EricH]

Originally Posted by Ian Curtis

Thread a nut on before you hacksaw the excess off, then unthread it off afterwards. It may turn off pretty hard, but it will clean the threads up significantly.

Or it'll help align the Dremel with a cutoff wheel, which doesn't mess up the threads as much... Oh, wait, that won't work in the pits, as it throws sparks. OK, so you do that at home and hacksaw at the event!

[engunneer]

Originally Posted by AdamHeard

-Smaller Fasteners. We try to only use #10-32 (which is killer strong if you check the math), and have now implemented #4-40's to supplement them in lower load spots.

The same math says never use #6-32. It has the worst strength to weight ratio in the #4 to 1/4" range, IIRC.

#10 and #4 will do 90% of what you need.

[DonRotolo]

Originally Posted by dtengineering

I'd also suggest building your robot a little under sized in each dimension

Quoted for truth

[lil'est lavery]

In DC, we were 0.1 over the weight limit, so we let the air out of the tanks for the pneumatics and ended up at 119.9