Hi all, I have begun to research gearboxes in hopes of designing our own either next season or for this coming off-season. I understand the great value of shifting, but what is the reasoning behind having a 3 stage gearbox, instead of a two-stage? Is it for easier gearing, or am I missing something here?
3 stage vs 2 stage comes at the question of how you’re trying to package your gearbox. For the same reduction (ex. 7:1), a 2 stage will require larger gears to attain the same reduction. Depending on how you want to package, each have their own advantages and disadvantages.
For drivetrains, it’s really up to you on how you want to do it. With the Falcons, some teams have moved to single stage reductions, while others have moved to 2 or 3 stages for a larger reduction for a larger wheel diameter.
For other mechanisms, the reduction needed mostly determines how many stages you want/need. For our intake pivot and turret gearboxes, I designed each with 3-4 stages for packaging considerations and for the larger reduction needed. JVN Design calculator is super helpful here.
I designed 3+ custom gearboxes for our 2020 robot, feel free to reach out with questions or if you want any CAD models/screenshots…
there is a preference for low stage count for higher efficiency (and backlash). if I recall correctly each one reduces the power by roughly 5%, albeit minor, it is still something to keep in mind, though not enough to prefer it over packaging and the like.
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Generally speaking the way I see gearboxes is to use as little stages as possible. This reduces backlash and allows for greater precision. The issue with single stage is that depending on your drivetrain speed and wheel size, your driven gear may end up being quite big which increases the chance of the gear hitting the floor or an obstacle. You can avoid this by having the gearbox extend below the gear to prevent gear damage.
The benefit to multiple stages is packaging as you can package a large reduction in a small area. Generally more stages are required with larger wheels as you need to slow down the motor more.
You ideally want to minimize the number of stages to increase efficiency, and weight. You will have larger gears as the expense though.
Having more stages will allow for more combination of gear ratios depending how you set it up. With a single stage, you are nearly stuck with that initial gear ratio, besides changing the pinion on every motor. On the second stage reduction, you could switch a 20:54 to a 14:60 if you desired with only having to change the two gears, and having the ability to change the 3rd stage allows you to get even finer adjustments if desired.
Would live some cad on your gearboxes
A 3rd stage is sometimes necessary if you want a large spread between your low gear and your high gear. Normally a large spread is not needed for drivetrains, but can be very useful for other applications. We used a 3 stage shifting gearbox for our elevator in 2018 because we also used that elevator for our climb. We could use the high stage for lifting the power cubes and get very high speed out of the elevator and then switch to low speed for hanging and have enough torque to lift the weight of 3 robots. I think our ratio spread was 3.68 between the low gear and the high gear.
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