4194B Drivetrain (Differential, Planetary, Pneumatics)

I am from team 4194B - Taipei American School from Taipei, Taiwan.

Planetary gear set up with a differential pneumatic locking transmission.


Our drivetrain has 6 motors in total, 4 - 393 Motors in torque config, 2 - 269 config. The difference is that 2 of the 393 and the 269’s can be switched to the drive train or to the arm. There are two dedicated 393 drive motors to ensure that we can continue to drive no matter what.

We do this by using a differential transmission system. The basic concept is by spinning the differential carrier, the frame that holds the center bevel gear, the output is split to two sides. However by using pneumatic to lock one side. All of the input goes to the unlocked side. We have two differentials, one for each side to keep them isolated from one another so we could turn.


When not lifting the arm, we lock the arm side and channel all the energy into the drive train. We have a planetary gear system that combines the input from the dedicated drive motor and the extra motors. The planetary gear system adds the rotation of these motors together which speeds it up. Furthermore, by controlling the speed of one of these motors, we can have torque mode by having but of these inputs working together thus lowering the rotations but increasing force. A benefit of this mode is that since the motors are working together, they won’t burn out.


We have CAD Models of the planetary gear system in an assembly file for Autodesk Inventor 2012, download the zip from this link

More pictures at this Picasa Album:

video link


i saw your “demo” robot base and we are AMAZED!
this is the best transmission i have seen in my life!
all you need to do is reverse the direction of one motor and that changes the speed/torque mode
it is nice, clean, and compact also
we are planning to make this the “new standard” in our region (credits to you ofc)
this is just truly amazing! :slight_smile:

:eek: :eek: :eek: :eek:

I heard about this at worlds, but I couldn’t find your pit LOL.

Wow. :eek: This thing is a beast.

Utterly brilliant piece of engineering.

I don’t know how it works, and it’d take quite a while for me to figure it out even with the pics and explanations, but I know this is really just amazing.

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Can you guys please post a close up video? Like showing how it works and all of that good stuff?
I’m sure everyone on the forum would appreciate it!

Also, I’m not sure if you remember me but, after seeing your display, we made a sloppy planetary gear system in our hotel room that night. We came by your pits to show you guys.

Two questions: 1, how much does it weigh? and 2, do you think it’s worth it for your team on your competition robot?

Very nice work, congratulations.

I studied this for quite a while; here’s my probable explanation. Correct me if I’m wrong, 4194b.

Also, this is GENIUS.

The gearing is split into two main parts: the differentials and the planetary drive. The “sun gear” of the differential is hooked up to a 393. Each side of the differential can be locked, transferring all the power to the drive/lift. The side of the differential hooked up to the drive powers the “sun gear” (chain) of the planetary gear.

Inside of differentials locked: outermost gears of differentials drive the small sprockets to the planetary gears, more speed.

Outside of the differentials locked: differentials drive the arm through the center pair of chains, the wheels are driven by the dedicated drive motor only, but at slower speed since the planetary gear chains are stationary.

to Mediumdave
You are correct on all accounts except one part. The differential powers the planets, not the sun gear. If you check the picture of the planetary, the sprockets are connected to the planets which then turn the sun gear.

to vdsa
The robot weights quite heavy, roughly around 17-20 pounds. The point of this system is to make use of idle motors, such as the arm lifting motors. By doing this, the motors are used more frequently. If its useful or not, it all depends on the type of robot. By adding this transmission, it adds weight. So it won’t be as agile, however it makes the robot more flexible. For our robot, our enemy was time and friction. We didn’t have enough time to further lower the friction in this system. If we could lower the friction in this system, we could have geared the drive to a faster speed, thus making it more agile. The primary benefit of this system is flexibility.


Wow. This is insane. I am totally amazed. You guys have done an incredible job on this!

Thanks for the link to the CAD too - I will be studying it for a while now.

Again, you guys have done an incredible job! :slight_smile:



This is ridiculously impressive, on too many levels to count.

A few questions:

Does the robot weigh that much because of your drive train or was it always like that?

Do you think that you could further lighten the drive train?

Are there any issues with tripping the breakers in the cortex? (I know they work together, but when you push someone else, would you stall?)

I’ve always wanted to link all the motors together so that nothing gets wasted. And you guys have done that WITH a 2 speed transmission. Just awesome :wink:

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In this diagram:

The red outer gear is called the sun gear, at least according to wikipedia. The differential powers a chain that acts as the red sun gear, right? Then it powers the planet gears.

Epicyclic gearing - Wikipedia <====sauce

Also, how many sprockets and gears are needed for each planetary gear set? I’d love to build one for fun, but it sounds really resource-intensive.

Goes to beg VEX to sell 6-tooth sprockets by themselves

Doesn’t the differential power the ring gear (the chain)? The two dedicated drive motors appear to be powering the planetary gears. (I’m that guy with the differential drive)

So in high-speed, were the dedicated drive motors (geared 5:3) powered, and if so I’m guessing the speed difference didn’t matter because they were adding with the 4 other motors?

mediumdave, the outer pink gear is the ring gear and the inner yellow gear is the sun gear. The ring gear is chain and sprockets in 4194B’s setup.

When I get back from St. Louis I’ll post a video of our differential drive (which is basically one of 4194B’s planetary gears but with a lock to prevent backdriving in high-torque mode, a problem they did not have because they didn’t use the 4 drive/arm motors on high-torque mode).

The red outer gear is called the ring gear. The yellow central gear is called the sun gear. Sun is in the center, with planets that orbit it, surrounded by the ring.


  • Dean
1 Like

It is things such as this that both scare me and continue to draw me back to the forum.

  1. WOW!! :eek: :eek:
  1. While this is amazing, I would also like to know if it is really worth all of the extra effort to build (assuming that it is extra effort for ypu guys). My team tends to keep the drive system pretty simple - usually just direct driven - but transmissions look really cool

i wish was anywhere even close to being that smart.

Whoopsie, sorry about that one.

This is truly amazing!!! :smiley: i am impressed