How does your team reduce weight on your robot?

I’m not doing this to pick on you, but I do want to make sure people understand the importance of wall thickness choices.

For an example, I made two 18" lengths of 6061 1x2 tubing. One is .125" wall, with a pretty extreme hole pattern on the 2" faces. Each hole is 0.5", to match a reasonably available drill bit, and the pattern is through both faces. The other is .0625" wall, unswissed.

According to Onshape:

Swiss cheesed .125" wall tube: 0.877 pounds.
Unswissed .0625" wall tube: 0.631 pounds…and a less sore arm from all the drilling.

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Ehh. If it’s for your drive train especially I wouldn’t recommend this as a weight saving tactic for most teams. Your drive train is the most critical component of your entire robot and if a gear dies (see Richard’s post above or any of the other number of dead aluminum gear posts on CD, this is not uncommon) then you’re dead in the water for at least a match. And it will be a very important match probably because it always happens at the worst time.

Usually accessing drive train gearboxes that are buried under mechanisms can be one of the worst things you have to work on during a competition too.

Do the fractions of a pound really gain you that much benefit over having confidence that you’ll never have to touch your drive train all season long? My suggestion is to find the weight elsewhere and stick with all steel gears in your drive gearboxes.

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Does the red make the swiss cheesed one go faster?

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On top of that, the plain 1/16" wall will almost certainly be stronger in most applications due to no stress concentrations caused by removing load-bearing material. I haven’t done the official analysis, but I would pick the unmodified tubing over the thicker Swiss-cheesed material any day.

Another option I’ve seen some teams do is put a lightening pattern but not have it cut through the tubing so as to retain the majority of the structural integrity, minimize stress concentrations, and loose some weight as well. This obviously is a LOT of work for what is usually marginal gains, but it’s a good option if you’ve already trimmed everywhere else (and you want to improve the cool-factor of the bot too).

Good example from one of my favorite robots this year:

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I’ve been working on cars for a long time…I’ve never seen aluminum gears in the drivetrain. But I have seen them in low load applications, such as driving the camshaft, where they outlast fiber gears.

Interesting to see who is advocating what concepts here. Mentorship in action.

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No, but stickers add five horsepower as always.

It is magnificent work, when a team has that option. Pocketed plates used to be in fashion for drivetrains in the late 2000s, especially down among the top Florida teams like 233 and 1251. But like you said, it’s very time- and labor-intensive for a small gain–and that’s if the machine access is even available to you. The average team thinking Swiss cheese is probably whipping out a hand drill, or maybe a drill press if they’re lucky.

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We Swiss cheese (#9 holes 0.5” OC) not so much for the weight savings but for the ease of positioning (and re-positioning) attachments.

This is a weight relief thread. Functional holes (even if they’re not being used for a function at the moment) are beyond the scope of both my demonstration and this thread. If you have the manufacturing capability to do those kinds of hole patterns, they’re certainly nice to have.

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Two birds, one stone.

Some of these strategies may be different if you are trying to just make the weight limit, or if you are trying to make a lightweight fast robot for strategic reasons.

Lately we’ve been chasing the latter. Ditching the pneumatics is my first go to, pretty much every other weight reducing idea has been mentioned so far. Fast robots are fun. 80lbs is about right.

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.196" holes, 0.5" spacing, top and bottom.

No holes: .631 pounds.
With holes: .618 pounds.
Delta: .013 pounds, or right at 0.2 ounces, or about 5.9 grams.

It may be two birds, but those birds are female bee hummingbirds.

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I guess I hadn’t entirely realized how great the weight difference was between thin and thick wall tubing as you demonstrated, even with lightening holes.
In my previous post, I had been primarily referring to methods used when the bot is at or over the limit right before competitions, compared to when the robot is being designed and constructed. When designing our robot, we generally try to use thin wall tube as much as possible, and as thin sheet metal as we can get away with.
Lightening holes are used as a last resort.

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Well, we have also 3 rows of holes on each side as well, so that’s ~1oz/foot.
Which I would wager ends up being a lot more than drilling a couple of holes in your drivetrain gears, which I believe I saw suggested here.

Three rows of holes on the sides would mean you have 4x as many rows of holes as I do (you have eight, I ran it with two), so your savings on an 18" segment would be .052 pounds. Or 0.035 pounds per foot. Or 0.56 ounces per foot.

With the calculated information: Bet.

am-0150: 0.425 lbs
am-3488: 0.25 lbs

Same tooth count, DP, face width, and bore; am-3488 is the weight-relieved version used in the EVO gearboxes.

The difference is 2.8 ounces in one gear, and in a drivetrain you’d be running at least two such gears. 5.6 ounces. (Repeat the exercise with the 40 tooth gears used in a Toughbox’s 5.95:1 ratio against its EVO counterpart, and it’s 4.28 ounces for two.)

Do some robots use more than 8-10 linear feet of 1x2 tubing? Sure! If I was overweight, would I advocate for adding a hole pattern in an at-least-two-often-four-setup process ahead of looking at those gears?* Heck no!

*For the record, I’d look at other things before even contemplating the gears. But we’re comparing two things right now.

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There are a lot of excellent reasons for a standard hole pattern in tubing. The weight savings from a bunch of #9 holes is miniscule enough as to not be “worth it” for solely that reason. It’s a great idea to do it from a modularity perspective (all of my teams’ robots do this), but for weight it basically doesn’t help.

Drilling holes or turning down steel drivetrain gears reduces their weight substantially - easily 1/4 lb per gear depending on the size. In terms of weight per operation, it really can’t be beaten.

Re: aluminum gears in the drive

We saw much more frequent aluminum gear-shredding in the drivetrain 2019, probably due to a combination of the 3x brushless motor drivetrain and increased amount of defense (and this was in COTS gearboxes). We took all the teeth off several 52t aluminum gears directly after the pinions that year.

That all being said, weight of steel gears adds up. Aluminum gears can still have a place in certain locations in the drive, but you really need to either be certain you’re fine to make it work ahead of time or keep a very close eye on the wear (and have replacements ready to go). Ex. we won’t run an aluminum gear on the output stage of the drive lower than 24t after our experience driving over the defenses and shredding teeth in 2016.

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Why would you not use a gear like the am-3821 which starts at 3.6oz? Or on one that size even an aluminum one.

Sometimes, it really does have to be a 50T gear. For example, a Toughbox-series gearbox can’t run a 52T gear (like am-3821 is) because there’s no matching 12T gear for the appropriate spacing.

Aluminum drivetrain gears have been discussed to death earlier in the thread. Emphasis on “death”.

Here are some of my favorite ways to keep robots light:

Pneumatic Systems

As mentioned previously, getting rid of this can sometimes drastically reduce total weight, but sometimes a few well placed cylinders can accomplish things lighter and better than motors.

General Fittings

Where ever you can, try to stick to aluminum fittings instead of brass. I can’t find exact PNs right now but they are available online.

Mainfold

Use an appropriately sized manifold. If you know you only need 2 cylinders, get a 3 port base instead of a higher number (1 overhead is usually good for later additions).

Special Fittings

Don’t use those giant pressure gauges or inline pressure regulators that come in the KOP and require brass fittings. Automation Direct has some really small and light push-to-connect legal variants you can find here.

Compressor

The standard FRC Viar compressor sold by AM is really good, it mounts well and is pretty robust. If you are really in the need for weight savings, there is this Thomas compressor. Be warned - it is more expensive, difficult to mount, and requires the use of bent metal tubing to be FRC legal.

Tubing

This is a weird one but for the 2020 season we only used 5/32’’ tubing and fittings on components post manifold. We found over previous seasons this worked well in select applications compared to the 1/4 standard variant and provides weight reduction, which can be important if you end up having pneumatic actuators on mechanisms with long tube runs.

Electrical Systems

Battery Wire

More of a design thing, but try to keep the battery, main breaker, and PDP close to each other. This reduces the length of large gauge wire that needs to travel between these components.

Specialized Components

When looking around for non-specific items, look for components with non-metal cases and the right amount of ports that you need. A good example of this is this Monoprice Ethernet switch we recently switched to vs this Netgear Ethernet switch that we used back in 2016/2017 because it was the first thing we found on Amazon.

Mechanical Systems

Drive Trains

Echoing what a ton of people said earlier, don’t skimp too hard on your drive train. Make sure your gearboxes are bulletproof and that the system will be able to keep up during competition. That being said, we have successfully used 1/16’’ wall box tubing for front/back frame rails. We have also switched out colsons/pneumatic wheels in the past for AM HiGrip wheels. We love them to death, even though they can sometimes get a bad wrap, and weigh a significant less compared to other wheel alternatives.

You can see the HiGrips and the front drive rail that we swapped out for 1/16’’ tube to get some weight back at a competition.

Pocketing

Don’t get too crazy with it, but something we found helpful was “scalloping” the edges of plates. All this is doing is getting rid of unnecessary attachment points between the plate and what it is providing rigidity to, which can net you good weight savings.

Pulleys

You can get away with 3D printing pulleys in a lot of cases. This not only helps with part procurement and integrating designs together, but also allows you to use belts and pulleys in a more creative way that can allow for a lighter mechanism than just using gears. A good example of this was in 2016, where the pulleys driving our wheels were printed out of PLA. They held up all season without any problems.

image

Intakes

People often design intakes with large rollers on them or lots of different wheels, with a giant hex shaft going through the middle. You often don’t need that shaft. Try to replace smaller wheels with a more lightweight roller supported on both sides and either a dead axle system, or a way to get rid of the middle unused portion of the hex shaft.

image
You can see inside the bottom transparent roller that the hex shaft driving the roller extended from the 3D printed tube insert to the bearing on the far side of the plate, retained on both sides by snap rings.

Bushings

Lots of cases where bushings would be a lighter weight, better solution than bearings. Good examples are intake pivots, mechanisms that drop down once a match, and other low load rotary points.

Hex Shafts

Thunder Hex from VEX has been a real game changer, but you don’t need to use 1/2’’ hex everywhere. VEX also sells a 3/8’’ variant which is perfect for intakes, rollers, conveyors, and standoffs.


Every shaft on our 2020 intake was 3/8’’ thunderhex, would have weighed a lot more with the 1/2’’ variant.
Thanks @JackTervay for reminding me about this one.

Turrets

They weigh a lot, don’t use them.

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So if we add contingency stickers everywhere, will i gain infinite HP?

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