Over the last few seasons it has become rather common to see shooters with adjustable hoods , and more specifically - actuated from the back of the hood with a “rack and pinion”, using a wide/long gear to move the adjustable hood (example in pic)
I was wondering, how are these gears made? (both rack and pinion)
Especially high load bearing ones like 2910’s one (in the picture).
Are they 3d printed? (if so, using what materials?)
are the hoods made from stacked laser-cut plates? (I’ve seen it on 971’s 2017 robot but cant find a decent picture)
I’ve seen quite a lot of 3D printed implementations of this design. I’ve personally done it on a Markforged, but I don’t think Onyx is really required to make this work. You can always bump up the gear DP for bigger teeth if you have a less precise printer, or go with something like a herringbone gear instead of a standard spur gear.
2910’s hood is made of 3d printed onyx. Additionally, the 3d printed parts aren’t really under much load. Most of the load is taken up by the side plates on the hood supporting the top rollers.
If you run a less precise printer or a bigger DP, your hood is less precise which hurts the accuracy. If you don’t have a markforged or something similarly accurate, I would suggest a different method of actuation, as there are many different viable ways of actuation a hood.
4020’s rack and pinion is 3D printed. Standard 20DP spur gear profiles. The pinions are made on a Markforged out of Onyx (nylon with chopped carbon fiber). The racks are made on an Ultimaker out of ColorFabb nGen PETG. We tried prototyping the racks from PETG to keep the cost down, but they have held up perfectly. We’ve had no need to print the racks in Onyx.
Hood is made from 1/8" 6061-T6 aluminum plate, cut on a CNC router.
and yet the force of the whole robot rotating (during 2910’s climb sequence)
is being pulled by one 3d printed gear tooth at a time. that’s really impressive
That rotating force isn’t as much as it actually looks. The hooks pop up to the center of their bot so it doesn’t take much force to tip the bot. Because their hood is so wide, it likely is quite overkill and would be unlikely to break (not a bad thing).
We found over the off-season that stacked laser cut wood worked quite well for the prototypes we used. We didn’t get a chance to battle test it on the field, but I would be willing to use it again (provided a few spares are made)
What this translates to in terms of overall system accuracy is made totally irrelevant by several other variables.
Backlash is easy enough to eliminate by simply changing the gear C-C; at low speeds and with deflection like this, a slight interference fit on the gears isn’t an issue.
The 10dp gear rack I printed on my Prusa mk3s worked out great all season.
Had a little backlash, but this didn’t seem to make a big difference. 20dp probably would have worked better, but we didn’t know at the time if we were going to machine or 3D print it.
Printed out of Prusament PC blend CF (as were many other parts on our robot)
Our students designed what we called the chonk gear. It was just a ramp that nested inside our shooter’s lower guide ramp. Using Limelight we’d set the angle based on distance. It worked pretty well. The initial ones were all PLA. Eventually made an Onyx version just due to some wear that we were seeing over time.
Yes. In the transition from our 2020 robot to its 2021 variation we considered adding an “infinitely” adjustable variable hood, but the math showed that it made little difference in shot accuracy, and that we didn’t even need 4 positions (for the 4 zones), so we went with a simple servo-actuated two position hood.
We looked at using gears for driving the hood. But we don’t like using 3D printed gears. There’s just a lot of load going through 3D printed parts. The real trick is to have the part layed properly on the print bed so that the thread that gets layed down has the grain direction so that you don’t create a week spot in the tooth profile. Basically lay it on the bed so that the teeth end up on their side. The gears need to be relatively wide to carry the load.
What we ended up doing is functionally identical, but we use a HTD belt. It is bolted through each end of the hood, then over a pulley on the motor.
Either the motor / pulley can be fixed, or the track can be fixed. (In the above example, the motor is on the rotating hood arms, and the track is fixed. )
The belt is the red line and the bolts are blue at the end.
What was the print time on that chonk 
