Paper: JVN's Mechanical Design Calculator 2016

#21

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.

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#22

Greatest tool in my FRC toolbox for sure.

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#23

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.

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#24

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

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#25

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?

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#26

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)

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#27

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

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#28

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

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#29

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.

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#30

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

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#31

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

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#32

Just a warning for anyone looking to use this calculator for the VEXpro 2-CIM Ball Shifter. The 3rd stage gearing options are reversed in the dropdown as compared to the picture and website. (Option 1 => Option 4, Option 2 => Option 3, Option 3 => Option 2, and Option 4 => Option 1).

In my haste to get an order submitted last night, I didn’t double check, so we ended up ordering the wrong 3rd stage gearing option. Oops!

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#33

For some reason I’ve been getting a lot of emails about linear gearing mechanisms that can lift 150-300 lbs. Weird, right?

I made this to help:

-JVN

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#34

For those people (like me) who sometimes have trouble finding a link to this thread and the latest version of my spreadsheet, I made an easy to remember URL with a direct link which I will always keep pointed at the latest version.

Hit up: johnvneun.com/calc

That’s…
[my name].com/[an abbreviated version of the world calculator]

If you can’t spell my name this trick isn’t going to help very much, and I can’t help you… Or at least I’m not going to.

As always, YMMV - enjoy the sheet and good luck with your season!
-JVN

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#35

Quick question about the two efficiency values:

From what I’ve seen, the “speed loss constant” is only used in determining adjusted drivetrain speed, while the “drivetrain efficiency” is only used to determine current draw per motor in a pushing match - are these two qualities related, and if so, why are they separate?

My initial guess was that the drivetrain efficiency is 90% and that the 81% comes from that efficiency being 90% efficient in it of itself (.9*.9 = .81), but I’m unsure if that’s purely coincidental or not. If that is the case, why is there efficiency loss at the wheel that isn’t translated into the motor?

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#36

The answer is that “speed loss constant” is a practical hack with basically no direct theoretical justification.

Read the whitepaper linked in my signature for more information.

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#37

First, I would like to say thank you for making this incredibly useful resource available, it definitely saved our elevator this year.
I have one question about how to use the intake mechanism tab. When you set the number of Intake Sides to 2 does it calculate as if there was one gearbox for each Intake Side or as one gearbox running each side? For example, if I set the number of Motors per Gearbox to 2 and the number of Intake Sides to 2 as well would that mean the the intake mechanism has a total of 2 or 4 motors?
Thanks again for this awesome resource!

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#38

So I’ve been trying to use the linear mechanism tab and for some reason the current draw per Motor isn’t calculated using the gearbox efficiency, am I using an old version or is their a reason for that?

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JVN-Design Calc Question
#39

It depends on how your intake is built. # Intake Sides is used to calculate the speed - a one-sided intake implies that the opposite side of the intake is stationary (and that the game piece is approximately round at least in the plane of the intake wheels). Note that the way Drag Load is used, this is “drag load per gearbox”. So, if you have the most common intake this year of independently powered dual intake (4 motors in your case above), you would only put half the total drag load here. If you have both intake sides powered off a single gearbox (2 motors in your case above), you would put the full drag load here.

It doesn’t make much sense to me, either. The gearbox efficiency only affects (in dependency order): Stall Load (G17), Loaded Linear Speed (F13) and Loaded Arm Time (G13). The rotary and intake mechanisms do the same thing. Caveat: Arm Time is based on “terminal velocity” only and does not account for the time required to accelerate the load from a stationary position to that terminal velocity.

Looking at a couple of drive tabs (Custom 1 and Custom 2), the drivetrain efficiency IS used to calculate pushing current (and nothing else) by dividing the traction limited torque calculated at the motor by the efficiency to get the motor torque required and the current from there. This usage I get.

If you want the gearbox efficiency to be used the same way in the linear mechanism tab, change the formula in F17 by inserting the four bolded characters as follows:

=((((F$5*C$8)-(G5*C$8))/(E$5*C$8))*(F$8*G$8**/D$8**/2*(C12*C13*C14*C15/D12/D13/D14/D15)/(0.2248*39.37))+(G$5*C$8))/C$8
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#40

Are there plans for the calculator to support the NEO Motor in the near future?

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