pic: FRC973 offseason teaser #2

Something using these gears (30 gears pictured, 10 of each style) will be competing at 2-3 offseason events this fall! We’ll upload a teaser a week or so until the full reveal. We might post a full .stp file of the robot when it’s finished.

They are all .125 6061 water-jetted out. Props to 148 for the inspiration and advice.

If you had a Dog gear with more teeth, like 6 (guessing by the gear on the far left). then the 4.5 lbs of force that the mini cylinder you posted might have enough force to shift a transmission. I bet those gears don’t weigh much at all, but if they weigh less then that chain in your drive-train then there might be an advantage to using them.

Believe it or not, these 30 gears come to a total of .99 lbs! That’s equivalent to just two 50T 20DP.

What is the PA and DP of those gears?

14.5 PA, 16 and 20 DP.

I love the gear with the matching window motor pattern. How many gears will you be stacking together per assembly? (If any)

Really cool stuff, can’t wait to see the big reveal.

Cool so did yall use a gear generator to get the gear pattern?

We’re stacking two per “gear” for all places these are used.

I actually used the formulas out of the Machinery Handbook to generate the curves. In hindsight, we made gears with teeth that were way too detailed. The specific waterjet our sponsor uses hesitates slightly before moving to each new curve, so the teeth had much more material blown out than if we had used a simpler tooth model (which would technically be less accurate, but would survive the cutting process better). We learned our lesson for next time here, but even with that flaw the gears still roll smooth on each other.

I have a feeling these are part of one of the coolest and lightest two speed gearboxes ever seen. Possibly as low as one pound flat.

I think I’ve got it.

Taking a leaf out of 25’s 2006 gear-drive locking drivetrain, are you?

Believe thats not what they are for :stuck_out_tongue:


Stacked together, these would make 2, 3 or 5 gears of each type. So my guess is that these gears will help 973 add 1-2 window motors to their shoulder joint that assists with anti-backdrive of their arm. Yet I dunno how that would affect their PID when doing ‘over the shoulder’ scoring (pick up from the front, rotate the arm and score at the back).

Their render from earlier this year:

At first I thought the middle gear would be used for a dog gear coupling where the dog gear only has 2 possible coupling positions (180 degrees from each other), yet that setup would shear the bolts/rivets holding the plate gears together. It’s an interesting design for a solid steel gear though.

Good guesses, but our arm this year was so ridiculously overpowered that PID wasn’t even needed to hold position, friction did it well enough. We did have PID of course, it just wasn’t what actually held the arm up.

What features of the gear tooth profile would you say were too complex/detailed/unnecessary? What features were essential, in your opinion? And lastly, would it make much of a difference to the tooth surface if cut on a laser as opposed to a waterjet?


It’s not so much what is essential/non-essential, it’s more about how much detail is needed; it’s the same feature either way (the tooth profile). The gear tooth profile is not just a simple arc, it’s a changing curve. You can approximate it as less curves and still get reasonable accuracy (which you’ll notice a lot of people/companies have done on their CAD models). I also imagine different machines might not get “confused” by the new curve.

If you google some about how to draw spur gears, you’ll see what I mean and it will make total sense.

I can’t make the blanket statement about water versus laser, just that the run of lasered parts we did this year that were .125 thick had a much cleaner and smoother edge than this run of waterjetted parts. I did tell the waterjetter to cut everything very fast though (to test if we get the same functionality out of less sponsor time), not sure how valid of a comparison that is. There are an awful lot of machines on the market as well, combined with the fact that machine settings can also have a huge effect on finish.

You probably mean how many points to use to define the involute. The involute can have a few points like 5 or 6, or many points like 20 or 30. You’ll get basically the same tooth form if the CAD software and/or waterjet blends the points together into a single curve. It sounds like the problem you had was too many points along the involute and the waterjet stopped / started before each point.

If anyone is interested in the math, I posted a spreadsheet in CD Media that creates a file to import gears into Pro/E. (It only does full fillet gears - sorry but flat root gears are against my religion.)

I’d be interested to give this a try, could you have it export the data in .txt for Solidworks?

Or into something else that more CAD packages can read?



It would be easy to modify if you can tell me exactly what the file format needs to be.

[EDIT] Actually, Solidworks may be able to read the IBL file - I found a reference to it in their online help. Give it a try and let me know if it works.

So I got a chance to check out gear tooth profiles in my work’s copy of the Machinery’s Handbook. DEFINITELY understand what you mean now about the curvature of the tooth haha.

To propagate the curve, how many points should I use if using a laser, or should I just use whatever the gear generator in SW does?

Thanks again!

GearGen is another quick and dirty way of generating a pretty good involute for gears.