FRC Mechanical Design Calculator (By Dillon Carey and Aren Hill)

#1

This link below will allow you to make a copy of the spreadsheet that both Aren Hill and myself have developed and used over the last couple years.

It isn’t quite as polished as I would like, but it gets the job done. Feel free to poke around and leave a comment if you find anything that seems wrong, have any questions, or any suggestions for future revisions.

Here is an index of what is included in the sheet currently:

Motor Specs
Motor Combiner 1
Motor Combiner 2
Single Speed Drive
Motor Analysis
Available Drive Components
Sprint Distance
Gears
Belts
Battery Stats
Wire Stats
Arms/Rotary
Choo-Choo
Winch
Shooter Wheel
Momentum Vs Traction
Pneumatics
Weight Analysis

Link to create a copy of the sheet:

https://docs.google.com/spreadsheets/d/1_JS2IudP2v3aj_PhyVQysM31IObV7KFWVXE1luA5Bp0/copy?usp=sharing

Paper: JVN's Mechanical Design Calculator 2016
#2

A nice bit of work! Thanks for sharing!

#3

Thank you and Aren Hill for putting this sheet together. It’s definitely going to be one of those calculators I refer to throughout the year for conceptualizing and designing robots and mechanisms.

#4

Awesome job. I think there are some improvements that could be made to the available power transmission components. I realize with Aren’s involvement, it’s going to be Vex-biased, but there are quite a few AndyMark gears not shown (particularly some of the odd-toothed gears), which can be useful for getting just the right reduction you’re looking for. It would also be useful to include dog gears and ball-shifting gears as well.

Also, the motor spec for some of the motors use the published specs rather than the tested specs.

#5

Awesome that this is finally public. Thanks guys.

#6

Adding the AM gear options would be useful. I would definitely still want to separate AM and VEX, to help reduce shipping costs.

As you can see, there is a distinct lack of any support in the spreadsheet for multiple speed gearboxes. This is because in my opinion, drive trains only need 1 speed (with verrry rare exception).

That being said, the dog and ball gears can be used on things other than drive trains, so I may add them.

This is definitely something that would be nice. Does anyone happen to have all of the test motor specs in a convenient spreadsheet format?

#7

Correct me if I’m wrong, but JVN’s 2016 design calculator has all of the tested specs I believe. Just go to the data page and you should find everything you’re looking for.

#8

This would be great. Perhaps use color coding to indicate which are available from which? (e.g. Blue = AM, Yellow = VEX, Green = both)

#9

This is AWESOME! Thanks!

#10

Thanks this looks very useful.

I just wanted to point out on the Gears tab the formula written in cell A2
CC=((N1+N2)/P)+O should be CC=((N1+N2)/(P*2))+O. It appears that it is correct in the actual calculation just not in the description.

Thanks,

Chad

#11

I’m wanting to resurrect this thread to ask a quick question. I’m looking at the Sprint Distance calculator, specifically the data table at the bottom. The data table also includes information about traction limiting and whether or not a drivetrain could break traction. Cell F29 references J25, and I believe it should be referencing I25 instead. J25 is the force limit at kinetic coefficient of friction, when I believe it’s supposed to be referencing the force limit at static coefficient of friction.

I’m pretty sure it’s just a slight typo, but I wanted to do a sanity check to make sure I’ve not made a mistake.

Thank you!

EDIT - Ok, now I’m looking at it again and I’m just not sure. I would think that’d you still use static COF for the moment the wheel starts rolling against the carpet, but I can see how it might not be as simple as that. But I also don’t think you would use the kinetic COF either. So is this an instance where the reality is somewhere in between? Or am I misunderstanding things?

#12

I was using this calculator for other purposes and took a glance at the pneumatics tab out of curiosity. I noticed a few potential issues as I reviewed it.

First off, you’re using PSIG for air consumption. You’ve made the units work out since you’ve also definited a minimum tank pressure. But your calculations would be more robust and potentially more useful if you converted to PSIA, instead. This would allow for a 0 minimum tank pressure term to still produce a valid result, and also can help compare to “free air” (useful for when you begin to factor in your compressor).

Additionally, all your force and air consumption values are set for extension, rather than retraction. For a single-acting cylinder that’s fine. However, a double-acting cylinder will have varying forces and air consumption when extending and retracting due to the surface area and volume occupied by the piston rod. A double-acting cylinder used in retraction will have less force (and consume less air) then when it extends. While you can chalk up the air consumption to a safety margin, the reduction in force may end up being important.

#13

The first thing I noticed as well. Our students figured this out the hard way a few years ago.

#14

This isn’t really that big a deal unless you’re using very small cylinders. The difference between extension and retraction force on a 1.5" bore (0.44" rod) and 1.06" bore (0.31" rod) cylinder is less than 9%. The difference on a 7/16" bore cylinder (0.19" rod) is more like 19%. It’s good to know that there’s a difference, but hopefully you have more margin than 10-20% in your mechanism.

#15

Obviously you should always be designing with a safety factor (margin) in your numbers, but you should be basing that safety factor off the more conservative force you get from the retraction.

And 10-20% is a pretty noteworthy delta. If someone were to come around saying you really get 10-20% less power from your CIM motors than you think, there would be more than one substantial thread discussing the concept and pouring over whether or not it’s worth switching over to MiniCIMs. :wink:

#16

The official CIM specs are plus or minus 10%, so you may actually be getting 10% less than you think.

#17

I guess I was playing too coy…