pic: Bit Buckets 2015 Offseason Drivetrain

[fb39ca4]

Very nice. Our team has had laser cut chassis for the past two years, but they are nowhere near as modular as yours.

[z_beeblebrox]

Originally Posted by fb39ca4

Very nice. Our team has had laser cut chassis for the past two years, but they are nowhere near as modular as yours.

Thank you. We looked at your team's robots when we were trying to figure out whether or how a laser-cut robot would work.

Do you guys have any experience with wood gearboxes or bearing press fits? We're trying them on this robot but won't have much time to test them before build season.

[fb39ca4]

Originally Posted by z_beeblebrox

Thank you. We looked at your team's robots when we were trying to figure out whether or how a laser-cut robot would work.

Do you guys have any experience with wood gearboxes or bearing press fits? We're trying them on this robot but won't have much time to test them before build season.

We've never done wood gearboxes, but bearing press fits work fine, you just have to make the hole a hair smaller than the size of the bearing.

Is your chassis held together entirely with T-slots? We thought those would not be strong enough, so we use wood glue for everything. It probably helps that you are using 1/4" plywood, rather than 3/16".

[asid61]

Originally Posted by fb39ca4

We've never done wood gearboxes, but bearing press fits work fine, you just have to make the hole a hair smaller than the size of the bearing.

Is your chassis held together entirely with T-slots? We thought those would not be strong enough, so we use wood glue for everything. It probably helps that you are using 1/4" plywood, rather than 3/16".

How small is "a hair smaller" for wood?
Press fits in metal are pretty precise. 0.001" smaller than the bearing is a light/ medium fit, whereas 0.002" is a heavy press fit, for the usual FRC bearings. Wood would be more forgiving on the size.

[fb39ca4]

Originally Posted by asid61

How small is "a hair smaller" for wood?
Press fits in metal are pretty precise. 0.001" smaller than the bearing is a light/ medium fit, whereas 0.002" is a heavy press fit, for the usual FRC bearings. Wood would be more forgiving on the size.

Like z_beeblebrox was saying, the number varies due to the laser kerf, as well as the softness of the wood. If you haven't tried it before, I would cut a test piece with different sized holes in 0.001" increments to determine the ideal size. The other option is cutting holes slightly too small and sanding the inside until the bearings press fit.

[z_beeblebrox]

Originally Posted by fb39ca4

Is your chassis held together entirely with T-slots? We thought those would not be strong enough, so we use wood glue for everything. It probably helps that you are using 1/4" plywood, rather than 3/16".

Everything is held together with t-slots.

Originally Posted by asid61

How small is "a hair smaller" for wood?

We've experimentally found that cutting the bearing holes .006" undersize compensates for kerf and gives a pretty tight fit. I imagine that this number varies with laser model and material.

[asid61]

Originally Posted by z_beeblebrox

Everything is held together with t-slots.



We've experimentally found that cutting the bearing holes .006" undersize compensates for kerf and gives a pretty tight fit. I imagine that this number varies with laser model and material.

Thank you, I will file that away for when we use wood.

[z_beeblebrox]

Here's the next version of the drivetrain. It maintains the same general design as the last iteration, but the CAD model has been completely redone. It is now better organized and entirely equation driven- the length, width, height and other properties can all be adjusted by changing numbers in a text file.

This model is not intended to be cut out as-is. It's intended as a base that a team can quickly and easily adapt to any game, changing the size, wheels, gearbox or anything else. As such, the gearbox mounting, which is intended as an example, is not equation-driven and the model includes no lightening or access holes, wheels or axles.

The electronics layout is also not a final design - it is simply a demonstration of how SolidWorks' blocks can be used to quickly draw an electronics board.



The gearbox included in the model is a repackaged Vex Pro Ball Shifter. Its only custom parts are the 4 wooden enclosure pieces.

SolidWorks files are available on GrabCAD here. Look in the folder "2015 Offseason Drivetrain v2 Upload".