pic: 2012 FRC971 Transmission Actual

[James Kuszmaul]

Originally Posted by DampRobot

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.

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.

[apalrd]

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.

[GDG 2337]

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.

[Adrian Clark]

Originally Posted by GDG 2337

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.

[GDG 2337]

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.

[M. Mellott]

Very nice design!

So it's my understanding that half of the final gear pair is attached to the wheel and the other attached to the transmission--please correct me if I misunderstood.

Was it easy to line up the gears and obtain/maintain the proper spacing when you first assembled the drivetrain and installed the transmission(just bolt it up and done), or did you have to make several tweeks to get the gears to line up just right?

[James Kuszmaul]

Originally Posted by M. Mellott

Was it easy to line up the gears and obtain/maintain the proper spacing when you first assembled the drivetrain and installed the transmission(just bolt it up and done), or did you have to make several tweeks to get the gears to line up just right?

As I recall, assembling the transmissions went well, but when we mounted it, there were a couple things which caused small problems:

• For some reason, one of the holes for mounting the transmission was the wrong size (too small), so it had to be drilled out by hand. It works now, but there was a flaw in the design at some point.
• The mounting bolts are tricky to access, with the shooter conveyor and all the electronics. The ideal place for getting an allen wrench to unscrew the bolts happens to be by poking the allen through the belly pan, and unscrewing a couple of the bolts. This is something we could try and improve on.

Overall, it went reasonably well, and come competition, we were able to switch transmissions relatively easily.