This year we had a 500:1 reduction from a neo 550 to 3 5:1 stages on a max planetary, then a 4:1 with a chain/sprocket. This would control an arm that would move down to intake, then up to shoot. Does anyone else have examples of really high ratios and what they were used for?
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We used a 1000:1 gear reduction on a Neo in 2019 to drive a four bar linkage to lift the robot onto the Level 3 hub platform. We used a 100:1 Cim Sport on a Neo, which went to a 2:1 chain sprocket reduction and then to another 5:1 chain sprocket reduction.
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Team 71’s file-card walking system comes to mind. Zero idea what ratio they had, other than “many”.
Outside of that, I’d imagine it to come up any time you have a fast motor (775 pro, neo 550) and a slow and small range of motion on the end effector (think, an arm or linkage that only rotates through < 90 deg)
In general big ratios start to introduce exotic failure modes. Like, where shock loads start shearing off gear teeth.
The VersaPlanetary Design guide is definitely good reading for folks looking to design with big ratios.
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2017 we climbed with a BAG motor at 270:1 in a VP.
My memory may be shot, but I think there is a lot more red in that table than there used to be.
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The higher-powered brushless motors are unsurprisingly better at crunching the gearbox internals.
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Pretty sure our arm in 2019 was 1058:1.
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This robot had a 710:1 total reduction with CIM motors for the arm (that’s ~7.5 RPM at full speed for those curious), with the design intent so it could lift ~35 lbs of game pieces with a 5ft lever arm.
Probably not the best design decision ultimately, but the robot did pretty good overall. We did strip a few worm gears.
2 CIM motors → 10:1 VPs → RAW Box (14.2:1) → 60:12 sprocket reduction
Hold this ratio : EDIT : This was the rotary gearbox mechanism for 1519’s arm in 2019
33 had a 2592:1 reduction for the climber in 2019 to be able to lift 3 robots onto HAB3. This fluctuated throughout the season as we played with the VP ratio, and we upgraded the last chain stage to #40 chain thus using different sprockets so that stage of the ratio got modified, but overall it was a very high reduction.
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I think RUSH had 1000+ :1 for their climber arms in 2019. Can someone please confirm?
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our 2013 tilt mechanism wa 3888:1
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Care to describe the transmission? I’m intrigued.
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We had a BAG motor doing our climb, geared through a VersaPlanetary to 343:1, then into a pulley system at 36:18 and finally into a spur gearbox at, effectively, 14:1. Total ratio is 9,604:1
It’s still at our first competition – we expect it to complete its climb next week.
our 2020 climber had a 3333-1 reduction to a neo 550 for the climber, we just pivoted around the high point on our bot to lift off the ground. used a versaplanetary 180 DEG 2-1 into a 100 to 1 versa driving a very large custom sector gear
We had a I believe to be 933:1 off each 775pro we used on our 4 bar climber in 2019.
This year the largest gear reduction we have is 16:1 on a NEO 550 on the bottom stage of our elevator.
On each side was 775 into a 3 stage 300:1 VP gearbox attached to a two stage custom gear box. Stupid overkill. It could and did turn a steel hex shaft into a pretzel.
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Leverage is an incredible thing…
Others have already posted large ratios, but the largest on a robot I had worked on was a 900:1 direct drive geared arm from 2791’s 2013 robot. The whole thing was built with VexPro aluminum gears in a custom box powered by a CIM (or was it a mini-CIM?). In some ways it was great - very easy to control without any kind of control loop (just an encoder and “stop when you see this number”…). The biggest issue was that the system was not shock isolated, leading to fatigue on the gear teeth and eventual failure. We bolted the gear to the arm to transmit torque but the arm was also riding on a big steel hex shaft - this too failed at some point if I remember correctly, though maybe that failure was in 2014.
A later arm used on 228’s 2016 robot learned lessons from this - we used a mini-CIM running through a 63:1 VP with a roughly 12:60 reduction on the arm. It turns out you don’t need a 900:1 gear reduction for an arm. Who knew? (Everyone knew.)
We knew our arm would be pretty heavy, so we didn’t want it to fall suddenly if something failed (we disconnected every match at our offseason comp this year so we were rightly concerned). I knew brake mode, especially on a brushless motor, could probably hold it back if the gear ratio was sufficiently large. I don’t know how a mini cim would perform, but for our neo 550 powered arm, 500:1 was about the minimum that would work and keep the arm locked.