This new version published for 2016 includes some small improvements.
Incorporates the “tested” motor values from motors.vex.com
Includes drop-downs to select motors directly from gearing sheets (or you can still enter your own numbers).
Includes sheets for design of drivetrains using VEXpro and WCP gearboxes (with drop-down selection of gearing options)
Includes a sheet for articulated drives (Butterfly, Octocanum, etc) with different wheel types, and varied gearing between wheels.
Some sheets have been simplified for inexperienced users.
Sheets have been tweaked to make it easier to have “multiple iterations” on the same worksheet.
Everything is iterative. Email me if you have questions or find issues!
Thanks for keeping this up to date! I’ve learned a lot just from puzzling out your earlier versions. I’ll definitely have to dig in this year on the calculations for the heteromotored gearboxes.
Speed loss constant accounts for the difference between actual speed and free speed of the motor. You can pretty much leave it at 81% for most FRC applications.
For “weight on driven wheels” if you have a 4WD robot with all wheels being driven then you would set that at 100%. If 2 of the wheels where non driven casters that would be 50% assuming a perfect weight distribution. Also for the purposes of this calculator omni and mecanum wheels are the same as traction wheels and wheel drop is ignored.
It’s an empirically-determined value, and will “vary from robot to robot”.
The 81% value is “about right” for the robots that team 148 builds.
“This is all very inexact. The calculations end up being “about right.”
“About right” is totally okay for a FIRST Robot.”
Stuff in quotes are excerpts from an old JVN post.
Your team can measure this speed loss constant for robots that your team builds, and eventually to get an idea if a different number would be more suitable for your team’s robots. The number depends not only on type of drivetrain and the design details, but also on craftsmanship.
Just wanted to bring this resource everyone’s attention. I’ve had a lot of teams contacting me this year asking for help on selecting gear ratios and motors for drivetrains, intakes, and hangers. The easiest way to walk teams through these calculations is the JVN calculator. It has tabs set up for commonly used gearboxes, rotary mechanisms, linear mechanisms, and much more. It also has motor specs for many of the commonly used FRC motors pre-loaded. I highly recommend that all teams take it for a spin. It’s a huge time saver and a great educational tool.
From our builds and testing, we have found the 80% overall ‘efficiency’ is a very good number to use. With so many COTS gearboxes available, the gear fits and alignments are great, so it is straightforward to put together a very good drive system.
Absolutely agree with Karthik. This is a great resource. We have used it extensively in the past, used it for our drive and lift in 2016, and are using it now for our drive and lift for 2017. In fact, a training session is on the agenda tonight for a wider group of students.
Chiming in too. We use this thing a lot and love it. We couldn’t build robots without it. Will also mention the VexPro load ratings guide for the VersaPlanetary gearboxes. Also very important.
