2168 Off Season WCD Prototypes

Our 2015 offseason prototype designs.


Transition from a fully customized sheet metal drivetrain to COTS that is fast to design, fast to manufacture, fast to assemble, fast to maintenance while maintaining performance, reliability, repeatability and durability. This transition to a COTS focus is taking place to shorten our build season and allow for design focus on key areas instead of the entire robot. All questions are welcome. Note: The CAD was developed to a point to support manufacturing and may contain re-build errors.

Two 8WD WCDs


Single Speed:
8WD - 4x1.5 colsons on spread-center 4 wheels
2" x 1" x 1/8" wall 6061-T6
#35 Chain / 1:1 12T Sprockets
3CIM Single Speed WCP Transmission (11.5 ft/s theo)
About 38 lbs. with transmissions


Two Speed:
8WD - 4x2 colsons on spread-center 4 wheels
2" x 1" x 0.1" wall VPRO tube stock
#25 Chain / 1:1 16T Sprockets
3CIM Two Speed WCP Transmission (5.5 ft/s and 17ft/s theo)
About 42 lbs. with transmissions

CAD is available here:


What are the square cutouts in the front of the frame for?


The pockets are for easy access to our bumper clasp hook mounting bolts and the encoder bracket mounting bolts (see the single speed DT).


We received several inquires on the bumper clasp part numbers. They can be found as follows:

McMaster 6139A27 Draw Latch, Zinc-Plated, 61 lb. Work Load Limit, 1-3/8" Latch Distance

Looks like a solid base that can be built quickly, nice work.

With a large number of people concerned about brownouts with running 6 CIM drive on the roboRIO, what testing have you guys done to look at current draw and battery voltage drop over time, and are you willing to share this info?

Looks great

What decided WCP gearbox vs. Ball-shifters?

Justin, we have our test fixture built and mounted which will bring the total robot weight to 150 lbs and we have our diagnostic code from 2015 downloaded, its simply a matter of putting the drive train in stall conditions and recording the plots. We have been in the middle of build season preparation and moving to a new shop space, so not much time has been available. It will be one of the first things we “prototype” week 1, subsequent to the testing, I will make the said plots available on this thread.

Rick, there were several driving factors:

#1 We only built the single speed version, because we had spare single speed WCP transmissions from last year and thus this made the project much more affordable.

#2 We personally are not fans of plastic gearboxes which can compress if over tightened and apply friction to the gear train. Otherwise we have no bad personal experience with the VPro ball shifters. In fact, we designed a single stage ball shifter with two variations of quarter-inch parallel plates and completely enclosed aluminum housing a couple years ago. If not for trying to minimize manufacturing time on components that can procured as COTS we would likely be running customized ball shifters.

#3 I was able to reach out to a number of engineering mentors from various teams who have used the VPro ball shifter and communicated their experiences with them. While there were various stated positives and negatives, a common theme arose relative to installation technique. In fact a number of teams I talked to that were relatively satisfied with the ball shifters indicated they had set up some variation of a dyno and tuned each side of their tank drive to be “synchronized” by adjusting the tightness on the gear box assembly bolts. Obviously with the proper software, the motor controllers could be used to overcome most of this. But it is rarely good practice to use software as a means to make up for mechanical deficiencies as a baseline approach. In the interest of not trying to come across as a “down with the off-the-shelf ball shifter”, I will be clear and say in none of my solicitation did I determine if the mounting of the gearbox was followed to exact instructions. That being said, we have always used Dog shifters in competition and thus are very familiar and proven with them. Additionally, as we are transitioning from sometimes custom transmissions and custom sheetmetal parallel plate drivetrains (for the last 6 years) to COTS WCD, we did not want to deal with the potential variability in performance and as we have not had the opportunity to physically ever test the VPro ball shifter off-the-shelf. Thus for us, the Dog shifter was the lowest risk approach to a highly reliable and smooth performing drive train.

As a side note / hopeful suggestion for the VPro employees who surf CD, we would be overjoyed if WCP and VPro partnered to package the ball shifter in aluminum plates with single and two stage options.