In order to aid VexU teams with making use of this season’s ruling that allowed vexU and VAIC teams to modify and use V5 motor cartridges and use their componets externally, I have reverse engineered the internals of the Green, Red, and Blue motor Cartridges. [Shoutout to RobotRevolution for sponsoring me with the motor cartridges].
These can be found at the following link: VexU-Configurable-motor-cartridge
The Top section, mid section, and gear included are all configurable iParts that can adjust to any ratio desired (1/6 inclusive to 1/2 exclusive). When entering a custom ratio in the parameters it will tell you the actual ratio that most closely matches the entered ratio, as well as the sun teeth and planatary teeth needed. The gear will promt you for the number of teeth and give you the pitch diameter in the parameters. For more details on iParts you may follow my tutorial found at: customizable-gear-for-vexu-and-vaic.
Additionally I included one custom cartridge, the Thanos cartridge which is 155.556 rpm as an example of how these parts can be used. This is the purple cartridge pictured above.
My key findings when reverse engineering these parts is that the gear is nonstandard as follows:
The pitch diameter (Pd) of the gear in inches can be found with the following formula:
Pd = 11 * Teeth / 500 + 0.0295
[the pitch is 45.4545 (fraction 500/11) with a static offset of .0295].
Addendum is 0.022875" ( fraction: 183/8000)
Dedendum is 0.027125" (fraction: 217/8000)
To get these numbers I measured the outer and inner diameter of each gear and plotted a best fit line in excel.
Because pitch is a linear relationship, the slope of these lines gives the approximate pitch. I then measured the shaft spacing in the 100rpm and 200rpm cartridges, and using the mathematical relationship of planatary gears along with the estimated pitch I was able to establish the addendum and dedendum (distance from outer and inner diameter to the pitch diameter). From this I then could directly calculate the pitch diameter of each size gear and plot them to establish the final formula.
I then double checked the results by using this formula to find the theoretical outer diameter and inner diameter of each gear and calculated the percent error of the measured gears. I found a maximum error of less then half a percent (0.5%), which is well within the manufacturing tolerance of the gears.
I have also included the Red, Green, and Blue cartridge files in the zipped file below, as well as the motor gear ipart:
V5_carts.zip (1.8 MB)
The top and midsection iparts are only available on my grabcad page previously linked.