Versaplanetary Output Direction

[feverittm]

I am going to change a question that might be a major Duh! moment.

Given a Versa Planetary with three stages a 5:1, a second 5;1, and a third 4:1 to make 100:1.

Now during competition season the ring gear on our 4:1 broke. For offseason repairs we replaced the 4:1 with a 3:1 and therefore we now have net 75:1 after repairs.

Now a question. Should we expect the direction of the output shaft to reverse with the change from 4:1 to 3:1?

I don't think so because that's not how planetary gears work. But I have been know to be wrong.

Thanks!

[Jay O'Donnell]

Your assumption is correct. The output shaft will turn the same direction.

[ollien]

Originally Posted by Jay O'Donnell

Your assumption is correct. The output shaft will turn the same direction.

Is there any situation, short of running the motor the other way, where a VP would turn the other way?

[Jay O'Donnell]

Originally Posted by ollien

Is there any situation, short of running the motor the other way, where a VP would turn the other way?

No. All of the stages turn the same direction, regardless of how many there are or what gear ratio they are.

[Max Boord]

The output direction should not change. Just out of curiosity why did you run 3 stages to get a 100:1 reduction when you could have done it in 2 and saved the space, weight, and money the additional stage?

[ollien]

Originally Posted by Max Boord

The output direction should not change. Just out of curiosity why did you run 3 stages to get a 100:1 reduction when you could have done it in 2 and saved the space, weight, and money the additional stage?

Correct me if I'm wrong, but the 5 5 4 will be less prone to breakage than the 10 10.

[asid61]

Originally Posted by Jay O'Donnell

No. All of the stages turn the same direction, regardless of how many there are or what gear ratio they are.

To add onto this, the reason why this is true is because the VPs use the carrier plate as the output. In a planetary gearset where the ring gear is held still (like the VPs) the carrier plate will turn in the same direction as the pinion. Thus, no direction change.

[Chris is me]

Originally Posted by Max Boord

The output direction should not change. Just out of curiosity why did you run 3 stages to get a 100:1 reduction when you could have done it in 2 and saved the space, weight, and money the additional stage?

The 3-stage version is stronger - check the load ratings document to see how strength improves with more stages. That tiny 10:1 pinion can't take as much abuse as the 3:1 or 4:1 stage can.

[Anupam Goli]

Originally Posted by Chris is me

The 3-stage version is stronger - check the load ratings document to see how strength improves with more stages. That tiny 10:1 pinion can't take as much abuse as the 3:1 or 4:1 stage can.

Although the 3 stage 100:1 reduction is stronger, it is more inefficient than a 100:1 using two 10:1 stages, right?

[Max Boord]

Originally Posted by Anupam Goli

Although the 3 stage 100:1 reduction is stronger, it is more inefficient than a 100:1 using two 10:1 stages, right?

Correct. it is also worth noting that the 10:1 carrier plate fails at 100 N-M while a stalled 775pro with a 100:1 reduction will develop only 71 N-M at stall neglecting the inefficiencies of the stages needed to develop the 100:1 reduction. in other words, unless you use the dual input stage or use a motor and gearbox combination not recommended by vexpro it should not be possible to develop the torque necessary to break the ring gear on a VP.

Also as someone who managed to accidentally stall a 775pro into a 100 to 1 versa (10:1 and 10:1) this season, I can attest that the 775pro will fail before the versa will.

[AdamHeard]

Originally Posted by Max Boord

Correct. it is also worth noting that the 10:1 carrier plate fails at 100 N-M while a stalled 775pro with a 100:1 reduction will develop only 71 N-M at stall neglecting the inefficiencies of the stages needed to develop the 100:1 reduction. in other words, unless you use the dual input stage or use a motor and gearbox combination not recommended by vexpro it should not be possible to develop the torque necessary to break the ring gear on a VP.

Also as someone who managed to accidentally stall a 775pro into a 100 to 1 versa (10:1 and 10:1) this season, I can attest that the 775pro will fail before the versa will.

You're able to develop more than the stall torque in FRC in two likely cases;

1) Reversing the voltage of the motor while still travling the other direction, this will results in a larger voltage across the motor than 12V, and generate higher torques (it stops being linear after the magnets saturate, unsure when that point is).

2) Dynamic and shock loads can cause brief torque spikes above the stall torque of the motor.

Unfortunately the above two make system sizing to avoid failure a little trickier, and for those reasons I would want to stay a good deal inside the Vexpro published ratings for the versaplanetaries to guarantee they keep running smoothly.

Voltage ramping (limiting the instantaneous rate of change of the speed controller output) can help alleviate the above two, but at the cost of acceleration time (likely negligible in most designs).

That being said, 330 has run them in quite large (but within spec) reductions the last two seasons on nearly all their systems with good success. I'm unsure if they do any voltage ramping or other tricks.

[ollien]

Originally Posted by Max Boord

Correct. it is also worth noting that the 10:1 carrier plate fails at 100 N-M while a stalled 775pro with a 100:1 reduction will develop only 71 N-M at stall neglecting the inefficiencies of the stages needed to develop the 100:1 reduction. in other words, unless you use the dual input stage or use a motor and gearbox combination not recommended by vexpro it should not be possible to develop the torque necessary to break the ring gear on a VP.

Also as someone who managed to accidentally stall a 775pro into a 100 to 1 versa (10:1 and 10:1) this season, I can attest that the 775pro will fail before the versa will.

Where is the 100 N-M stat located? From what I see, the load rating guide only includes safe ratios.

Or are you calculating the torque from the safe ratio?

[Max Boord]

Originally Posted by ollien

Where is the 100 N-M stat located?

The 100 N-M number is from page 13 of this sheet. Im assuming that the 1/2 inch hex or round shaft is being used causing the weakest link to be the carrier plate as the shaft fails at above the force the carrier plate can withstand.

[troy_dietz]

Originally Posted by AdamHeard

Voltage ramping (limiting the instantaneous rate of change of the speed controller output) can help alleviate the above two, but at the cost of acceleration time (likely negligible in most designs).

That being said, 330 has run them in quite large (but within spec) reductions the last two seasons on nearly all their systems with good success. I'm unsure if they do any voltage ramping or other tricks.

The voltage on our arm motors is ramped. The motors are redundant, but we would likely have issues with our srimech if one was missing.

We have had issues with the carrier pins coming out occasionally, we're planning on welding them in place.

Since 2014, all of our arm VP's have led to an 5:1 chain reduction (the large yellow sprocket). I believe 2013 has a double chain reduction.