Reducing the weight of our intake

So we built our intake but then we found that it was way too heavy for our lift to support without bending it.
Our intake looks like this from the bottom:

and mounts like this:

We have some ideas for getting rid of some of the weight and support the second stage when it’t fully extended. We just wanted to see if there were any suggestions on what we could do without rebuilding the intake

Some of these would require rebuilds but things to consider.

  • There are a lot more shaft collars than are needed. You have bolts in the end of the shafts so you should be able to make quick plastic spacers that will be a lot lighter than the shaft collars.
  • cut holes in all the sheet metal or replace it with lexan
  • switch to VP lites instead of standard VPs, also BAG motors or AM 9015s are lighter motors
  • belts instead of chain
  • thin wall 1*2 instead of the .1 versaframe, though holes are probably quicker
  • swap from bolts to rivets

We have a very similar design…

Thought of Lexan ?

We did our arms a bit different but out of poly carbonate
With 9mm belts and 3d printed sprockets.

I will try and get a weight of the intake for you the weekend.


Will take a look into some of these ideas! Thanks!

We did originally try with lexan, but we had issues with the rigidity. It’ll be interesting to see your weight! Thanks for the reply.

Speed holes!!! Not only are they functional they look good if done right as well.
Perhaps speed holes in the form of your team number? I know that’s on my hope to do list.

Build a stronger lift?

This is highly dependent on your axle loads, but also consider swapping hex axles for Churro. At 0.16 lbs/ft, it is appreciably lighter than regular hex shaft (0.27 lbs/ft). (3/8" is 0.15 lbs/ft, which is not zero but is definitely diminishing returns since you’d be swapping a lot of stuff out for the new bore.)

If you can’t run belts, at least consider #25 chain.

If you can’t use rivets (and please, give real thought to using them), at least keep the bolts as short as they can be. Hard to say what you’re using by the pictures, but I like #10s for situations where things may get a little rough.

The outer arms as mounted have the chain running below the compliant wheel. Can the complaint wheel go on the bottom? That would let you shorten up one shaft significantly.

And while you had trouble with lexan rigidity, consider lexan with a bent flange or lexan reinforced in the necessary places to stiffen it up. A thin piece of angle can add quite a bit of rigidity (indeed, that’s how FIRST did it on the hoppers on last year’s field).

We are working with a different poly-carbonate product this year.

Similar to this

Have some left from for our shop renovations that are in progress.


What is the whole robot likely to weigh now? It looks incomplete so just pile on the components that are not yet installed and add a few pieces of sheet and tubing to approximate other mechanisms you have yet to build. Reducing the weight of your intake by, say, 3 pounds will take a fair amount of effort but it will be a nasty surprise if your total robot weight happens to be 20 pounds too high. On the other hand, if you are 20 pounds under the limit, you know you can do things like add a stronger structure to hold your intake and/or add motors to lift it.

I hope that is just extra shiny aluminum or plated and not stainless steel. If it is stainless, switch it to aluminum.

If you are using 1/8" wall tubing, you might be able to replace it with 1/16" tubing to save a small amount of weight. Test thoroughly before committing to ensure it is still strong enough under all conditions.

You could consider taking that 2x1 out of the center and replacing it with a few standoffs.

What you need to do is add some lightening holes. You can cut the weight by a third with little change in strength.

Easy if you have a big CNC mill. My team does them with a conduit punch.

Once when I was a young engineer, my boss told me my design was good, but needed some lightening holes.

I didn’t get it at first. I said “how big of hole does lightning make?”

Some of this reiterates what’s said above, some of it doesn’t:

You have way more structure there than you need – plate with lots of lightening holes, spaced with standoffs, will be shockingly strong (and will allow you to get rid of the box tubing on the central piece altogether).

Ditch the shaft collars, retaining bolts, and washers in favor of clip rings (you’ll need a lathe*, but once you start doing this you’ll never go back.)

Those other shaft collars can be replaced with nylon or PVC spacers (you can buy them or just cut them to size out of a piece of PVC–the latter is ugly but fast and functional) OR with more grooves and clip rings to hold everything right where you want it. (I prefer spacers for spacing, because it is both faster and more adjustable, especially when you have lots of spacers in lots of sizes to choose from, but clip rings will be lighter.)

Ditch the wide box tube on the arms in favor of 1" box with VexPro end effector gussets.

Ditch the bolts for rivets.

Use belt instead of chain if you can, and if you can’t, use lighter chain.

Use BAG motors–they’re light and plenty strong to do the job on an intake.

All that said, once you’ve lightened that as much as possible, you’re going to be adding the weight of a crate and then driving around/getting hammered by other robots, so if your lift mechanism is straining under the weight right now it may definitely strain under those conditions even with a lighter mechanism, so you might want to consider a redesign to a stronger lift.

*you can cut clip ring grooves with a drill press and a hacksaw, but I wouldn’t recommend it

This style design was really effective for those large totes in recycle rush but I wonder if it may be a bit overkill for these powercubes. In some of our early testing just two wheels on a spring loaded arm was surprisingly effective. Take a look at the many videos available from Ri3D, etc. Just remember any extra weight up high really puts you at risk for tipping over.

swiss cheeseing with a drill could start to get your weight down, I also like the polycarb idea, Polycarb could also add some flex to your intake to make up for the strength lost by swiching from aluminum.

What shape/design do teams usually use for the lightening holes? (I’m assuming triangles/rhombuses, but is it some sort of tessellating pattern?)


If you have CNC access you can do lots of things, if you are doing it by hand, get a hole saw and some cutting fluid, and get to work.

Belts belts belts. Those chains and sprockets are much heavier than you realize, and their high-torque performance is unnecessary for an intake.

Other than that, I can’t say much more than anyone else has already said- thinner material, swiss-cheese every plate, and switch to churro instead of steel hex.

And a deburring tool such as this or this. Figure on spending about as much time deburring as cutting the holes. It’s probably best to do it all before a Robot Inspector tells you to do it.