Gearing up low-RPM motors vs. Gearing down high-RPM motors

In general, will gearing up a lower-RPM (200 rpm) motor have a different result than gearing down a high-RPM (600 RPM) motor to achieve the same net RPM? Will there be a difference in acceleration, physical power, etc.?

From what I’ve seen on the forum, it is better to gear down a 600 rpm because the 600 rpm cartridge is more direct (6:1). I.e, it uses fewer gears compared to gearing up.

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But I guess the rpm, torque, etc, is the same? It seems logical. You’re saying the difference is in his much space it takes up?

Theoretically, yes. All of the torque, rpm, and other misc. stuff would be the same. I only know this from what I’ve seen on the forum. I would guess that less gears would, first, make the actuation time much lower, and less friction because of a lower amount of gears. When i mean actuation time, I mean the amount of time between the motor starting to move and the actual robot moving. The physical size would still be the exact same, the only difference is the cartridge.

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forgot to add this in, but besides power, would the 600 rpm motor option be more prone to overheating?

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From a theoretical standpoint, it would make no difference how you obtain your final gear ratio, whether internally or externally. However, real life is not theory and we must take into account efficiencies and friction. The fewer gears involved in the gear train, the higher the efficiency and the less friction in the whole system; therefore, it would be best to use a gear cartridge to get the ratio as close as possible to what is needed, and obtain the remainder of the ratio, if needed, with a simple single gear solution.

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I believe (someone correct me if I’m wrong) that 600rpm cartridges have fewer internal gears than the other two, and thus less internal friction.

Additionally, gearing up 100 or 200 rpm cartridges would involve backtracking of sorts from the internal motor, where the cartridge gears it down, and then you externally gear it back up again, which can be redundant and add more friction and slop.

Also, gearing down 600 rpm will have less slop than gearing up 100 or 200 rpm, because the slop from the motor is reduced in the gearing, where when gearing up, the slop is amplified.

So I try to gear down from 600 when it makes sense to, such as on a drive or intake.

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Can confirm this is correct. Blue cartridges have only one planetary state, while green and red cartridges have two. Having less stages also give two extra benefits. First, the cartridges are lighter so it counts toward weight reduction, and having one stage results in significantly less motor slop (which is really the only slop that should exist within a chassis)

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This makes sense. If I’m not mistaken, I think the actual first shaft that is spun inside the motor is going very fast, and VEX gears it way down inside what we still consider the motor, so that once it gets to the hole where we stick our shafts, it’s already geared down a lot. So the 600 cartridge would still be gearing it down.

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For those who are interested, the input gear into the cartridge spins at a top speed of 3600rpm. Inside the motor cartridges are either 1 or 2 planetary stages (1 for 600rpm, 2 for 200 and 100rpm).

The first planetary stage in all 3 types of cartridges have a 6:1reduction ratio.

3600 / 6 = 600

This means that the input to the second stage for any cartridge will be 600rpm.

In the 100rpm carts, the second stage is also a 6:1 ratio.

600 / 6 = 100

And in the 200rpm cartridges, the second stage is instead a 3:1 ratio

600 / 3 = 200

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Unless your gears have no lash (space) then there’s always slop in a powertrain.

slop begins:
gear cartridge
output shaft to metal shaft
metal shaft to input gear
input gear to output gear
output gear to metal shaft
metal shaft to wheels/device/arm/etc

Some of these are larger than others, but they all add up.

And, all else equal, I’m in the ‘gear down a fast cartridge’ voting group.

Sure, let’s have a vote. We can all kind of see what the consensus is, but let’s poll to see if anyone disagrees.

What does everyone think, given these options?
  • Gear up a slow cartridge.
  • Gear down a fast cartridge.

0 voters

And let’s say, please only vote if you didn’t get your opinion from reading this thread.

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