Machines 2026 Competition

[greyd]

Hello there,

I am doing Machines B this years and its my first year doing SO. I have a few questions about the event. I think that I am using plywood or MDF as a base for the fulcrum.

1. What is the optimal length of the beam?
2. What is the best material for the beam?
3. Is the hangar loop for the mass provided by the ES?
4. What are good options for some ball bearings to use?
5. What is an appropriate way to connect the beam and fulcrum?
6. What are good designs for the fulcrum?

Thank you,
Grey D
Division B

[Unome]

Hello there,

I am doing Machines B this years and its my first year doing SO. I have a few questions about the event. I think that I am using plywood or MDF as a base for the fulcrum.

1. What is the optimal length of the beam?
2. What is the best material for the beam?
3. Is the hangar loop for the mass provided by the ES?
4. What are good options for some ball bearings to use?
5. What is an appropriate way to connect the beam and fulcrum?
6. What are good designs for the fulcrum?

Thank you,
Grey D
Division B

1. I'd recommend a cm or so under the max length. Nationals caps at a ratio of 7.0, so you can e.g. place one mass 5 cm from the fulcrum and the other will go to at most 35 cm on the other side. Accuracy for this event's device portion is generally pretty straightforward so no need to push ultra close right up to the 80.0 cm limit.
2. We used some sort of solid wood when I competed, which should be sufficient - maybe there is a better option, but it won't be so much better as to matter unless you're already in the National medaling range and trying to eke out every advantage possible.
3. Yes, it's part of the mass so it's provided by the ES.
4/5/6. We used some sort of metal rod directly through a hole in the wooden beam. If it's a reasonably precise fit and the beam can rotate easily, that should be sufficient. Getting negligibly close on accuracy is not too complex, it's getting a fast time that really helps your score a lot.

[GlitchyNebula87]

Hello,

First time doing Machines B but anyways do the instructors give you the box to put your weights in or do we have to make our own?

Btw this is in Redmond



Thanks

[knightmoves]

You don't bring weights.

You bring a class 1 lever device. The ES provides you with three weights (labeled A, B, and C). Your job is to use your lever to determine the ratios A/B and B/C. The rules describing the weights (must fit in a box of particular size, must be able to fit golf ball through loop of string or whatever) are for you to ensure that the device that you build can accommodate the weights that the ES will have.

[greyd]

GlitchyNebula87,

I would recommend watching this video to understand the Division B competition this year. https://www.youtube.com/watch?v=jGMgPnRHsx0

[GlitchyNebula87]

Sorry for the confusion.

I am trying to ask if the instructor give us the box for the mass or do we make the box on ourselves. Or if we can use strings to hold the masses. This part is not clear in the rules.

[knightmoves]

Sorry for the confusion.

I am trying to ask if the instructor give us the box for the mass or do we make the box on ourselves. Or if we can use strings to hold the masses. This part is not clear in the rules.

Usually, if you think the rules aren't clear, you need to slow down and read through them carefully again.

In this case, there is no such thing as "the box for the mass".

The rules require that the mass, when the loop is fully stretched, fit within a 15.0cm x 15.0cm x 20.0cm box. An FAQ clarifies that the 20.0 cm is the vertical dimension. There is no actual box - this is to tell you what size of mass you need to be able to accommodate on your device.

As explained in the rules, the ES will provide the masses, and these masses will have a flexible loop (made of string, fishing line, zip ties etc.) large enough to pass a golf ball through.

The expectation is that you would use this string to suspend the test mass from your device, but it isn't actually required. You could, in theory, build a wide beam and rest the masses on top of it. You'll probably find it more difficult to judge where the center of mass is if you do that, though.

Rue 3d explicitly says that you may have movable lightweight hooks that you hang the masses from. You don't have to - if your beam is smaller than a golf ball, you can pass the string directly over the beam. The implication of this statement is that you may not have movable pans or other heavier components to support the mass; you wouldn't want to do that anyway.