pic: 2012 FRC971 Transmission Actual


Here’s a look on our transmission for 2012.

Inverted placement of motors, 2 speed (7’/16’)/sec, single reduction, alum gears, pressed on hex adapter, .090 laser cut side plates, mounted fan for motor cooling, pancake piston, hexed alum shafts

Very lightweight and simple to assemble and mount. The kids are making better designs every year.

Really like this setup! You guys had a great bot this year!

Do you have an overall weight for the transmission? It looks very light weight, plus with AL gears.

This is a very nice looking gearbox.

How do you mount the two gears to the output of the CIM that allow you to do single reduction?

What is the part number/soruce for the pancake cylinder they seem really useful in this application.

Not entirely sure what you are asking here, but the way the gears are mounted to the CIM shaft is by pressing a hex sleeve over the CIM shaft, then using the hex to mount the gears. If I remember correctly, then the smaller gear is 15 tooth, the larger is 30, and then the two gears in the second stage are 60 tooth and 45 tooth, respectively.

Bimba FO-020.3-3FMT

That’s exactly what I was asking, thank you for the quick response.

If I were to design up a transmission like this, I would get a lot of flack from the programming leadership about not including space for an encoder. Did you end up including one that we can’t see, or was there an argument for not including one?

Most teams who do WCD end up just connecting an encoder to another wheel(any of the front or back wheels) and then zip tying the encoder wire down to the bellypan. I can speak for 971 but I assume they did this too.

971’s drive wasn’t a WCD, and since they used dead axles, I doubt this was the method they chose.

This is actually beautiful.

Man, you guys make some of the nicest robots around.


The encoders aren’t part of the transmission. They are off on the back wheels on a plastic gear I believe.

And just to be clear, did you ever end up using them? In my experience, they are often a pain to design in, and not that useful for the programming team.

Why do you find them to be not very useful?

And just to be clear, did you ever end up using them? In my experience, they are often a pain to design in, and not that useful for the programming team.

If you just use the AM encoder bracket for the E4P ts really straight forward to design them in; from memory I think its something like .75" out to each side and .1875" down for the mounting holes with respect to the shaft.

Pretty easy to design in. Just drill a 1/4 hole and shove a s4 in. Literally no work at all.


The theory always seems to be that they will get used for autonomous tracking or smoothing out driver control or something. Because the programming team seems to have so much trouble even getting basic functionality, they never end up getting used.

I don’t mean that it’s hard to design in two drilled holes. I mean that often both sides of the output shaft are used, so there is no easy place for an encoder.

Thanks for the tip about zip-tieing the encoder to the bellypan, and putting it on a wheel shaft. Wouldn’t that cause them to rotate off axis?

The encoders were/are used.

The encoders are mounted to a hole on the inside of the drive train, and are driven by a pair of plastic gears, one of which is mounted against the wheel, the other on the encoder. We have one encoder on each front wheel, although because of our ball intake and barrier-traversing skids, the space in the front of the robot is crowded, so it might’ve made sense to put the encoders on the back wheels.

Encoders are very useful.

Common algorithms I’ve implemented with drivetrain encoders:

-Autonomous straight driving with speed control, distance thresholds (each side has a speed controller and stops when distance hits a target)

-Autonomous straight driving with a dual distance controller and distance error controllers - Each side has a distance controller. The steering input is calculated from the integrated distance error (sorta like using the distance delta between the sides as a heading input in an I-controller gyro steering loop).

-Autonomous straight driving with dual distance controller and gyro heading correction - This is my favorite. Each side has a distance controller, plus a single steering controller based on gyro feedback primarily using an I term. When properly implemented and tuned, this is my favorite autonomous driving algorithm.

-Autonomous stop decel controller - We drove fast enough to jump on decel, so we implemented a PI controller to do a controlled decel. We could play with the PI gains until the decel was repeatable.

-Teleoperated speed control - Each side has a controller for speed, allows you to “push through” in situations where you request partial power. You can also straight drive when one side is unable to meet the demand by lowering output power on the other side, which is sometimes also used by trans algorithms.

-Automated Trans control algorithms often rely on encoder speed feedback in addition to driver demands. Some downshifting cases are primarily based on vehicle speed and/or acceleration.

Some of these controllers are more useful than others. I highly recommend playing with some autonomous controls during the off season, since they are often a large factor in autonomous reliability. Simply measuring distance and stopping at the right time can make autonomous significantly more reliable in most games.

To make the design even more compact rotate the CIM motors like Killer Bee’s (FRC 33) 2011 design and use the CIM motor bolts to hold the transmission halves together.

Assuming I understand you correctly and what you’re saying is that the CIMs should be rotated so that one of the mounting bolts can be used to mount the standoff: if the CIM was rotated in such a way then one of the bolts would be behind that massive low-speed dog gear. Although mounting gearbox standoffs to the CIMs is a great way to simplify the design, in this gearbox because of the way they gear their CIMs, the CIMs are much closer to the dog gears making it so the CIM cannot be oriented in any way much different than its current orientation.

In IanW’s Robot Tutorials, see Making a 2-Speed Custom Gearbox for pictures of the concept. The long 10-32 screws can be found at specialty nut/bolt places. I bought ours at Mid-State Fasteners, they are pricey.