# Paper: JVN's Mechanical Design Calculator 2016

Wow @ the 550 power. I now get why we had issues with our elevator last year. Thanks for testing the 550.

Thanks for the effort you put into - and for sharing - this universally valueable tool

This is the first time I have worked on a drive base, and so I wanted to make sure that I was doing everything correctly.

1. For the “Weight on Driven Wheels”, that weight is distributed evenly among wheels, right? (say 25% if there are 4 wheels)
2. What is the “Speed Loss Constant”?

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.

Can a brother get more stages in the Rotary Mechanism tab for the 2017 version? I need more than 4 stages please.

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.

Has any free technical resource had a greater impact on the design quality and competitiveness of FRC robots than this calculator has? I seriously doubt it. This continues to be an essential tool for any FRC designer, and I’m so glad it continues to exist and be updated with useful features.

Greatest tool in my FRC toolbox for sure.

It’s such a fantastic cheat code. I assume the existence of the calculator is JVN’s property so it shouldn’t get re-hosted where he wouldn’t want it… but that being said, I wish that if I could pick one resource to put on any and all FIRST related websites, any tangential email blast, write in the sky, etc., it would be this.

I am not an engineer or studying for a career in engineering but this tool has unlocked a lot of doors for me and my team.

Thanks John! Great work, super helpful to us EEs!

I love this tool, it’s done wonders for us in determining reasonable motors and gear ratios to use.

I do have a question though- For the Intake Mechanism tab, how does one determine a reasonable drag load?

New version (2/14/2017):
Fixed an error in the Intake mechanism sheet which applied the load based on the pulley diameter instead of radius.
(Yes, that means I forgot to divide by 2 at some point)

Ahh, well I guess that explains a few things. :rolleyes:

Wel, that explains why we thought we needed 3 775 pros for our intake… well, overkill never hurt right?

On the bright side, having teams across the country add more power to their intakes than necessary will only result in higher quality intakes across the board. That’s really the only “secret” to a good ball intake other than material - just throw power at it.

cant find the link to the new one in the media section.
Searched on JVN, only found old ones.
Where is the new one?

Click on the link in the OP, its the last one in the list of edits.