I made a geogebra model to see what would work and what wouldn’t for getting the Generator Switch Level.
Here’s a download if you want:
Generator Switch.ggb (23.9 KB)
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Is the variable that has a range from 0-200 -> weight?
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Yes it’s the robot weight in pounds.
This is super nifty - thank you!
Did you account for switch weight? It would shift the COM slightly towards the center.
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Just want to say that this is fantastic. Thank you so much for creating this!
Yes this includes the switch weight.
The main thing that it’s missing is when the robots aren’t hanging exactly vertically.
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Also missing tandem climb options - allow up to 450 lbs weight perhaps?
thanks, this was very useful!
What about robots that attach rigidly to the bar, this doesn’t properly model the hang angle when the robot CG can’t swing as the bar rotates.
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Yep, including a variable for a rigid attachmet vs a pivoting attachment makes a non trivial difference in the system response.
Essentially, a rigid attachment lends itself to helping stabilize/balance the system.
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Could you explain the physics math behind your model? What equations are you using to calculate the angle?
Very helpful visual tool. Thank you!
All I’m doing is calculating the center of mass of the switch+robot system (the weighted average of the switch COM and the robot COMs) and then finding how far that point is from vertical. So I actually managed to avoid doing pretty much any physics.
This is critical.
Very nice. thanks for creating this.
When I saw the endgame details this year, I immediately wanted to know how difficult it would be. This led to “what are the limits”? After some trial an error I settled on table that illustrates nominal, good, marginal; and no-go parking positions for different robot weights. Please refer to the pdf that explains the problem, assumptions and derivation of the equations for more details.
The Excel sheet is also attachted.
Endgame_2_Robot_Balance.pdf (763.4 KB) Infinite_Recharge_2_Robot_Endgame.xlsm (1.0 MB)
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For those interested in the equation used to calculate the angle of tilt for various configurations, I have provided it below. This assumes that robots hang vertically as the generator switch tilts. Rigid robot attachments would be more difficult to calculate but not impossible, as you would need to know the (x,y) coordinates of the center of mass of each robot relative to the pivot.
I have generated an equation to calculate the angle with respect to the vertical for the generator switch (see 2020 FRC game details) with three robots attached. The equation gives negative angles for clockwise rotations and positive angles for counterclockwise rotations. For positions to the left of the center line, negative distances must be entered.
- Let M1 = mass of robot 1
- Let M2 = mass of robot 2
- Let M3 = mass of robot 3
- Let Ms = mass of generator switch = 93 lb.
- Let D1 = horizontal distance of center of mass of robot 1 from center line
- Let D2 = horizontal distance of center of mass of robot 2 from center line
- Let D3 = horizontal distance of center of mass of robot 3 from center line
- Let L1 = height of generator switch (from pivot to horizontal bar) = 48.375"
- Let L2 = height of center of mass of generator switch = 26"
Equation 1: Angle calculation for 3 robots hanging from a generator switch.
Enter whatever masses you want for your three robots – the units cancel so as long as you use pounds or kilograms exclusively, you should be fine.
Remember to use negative distances for D1, D2 or D3 if they are left of center. The choice of units is up to you as long as you use them exclusively. This equation is only valid between the hard stops on the generator (roughly ±14.5 degrees).
I have no “dog in the fight” as I am no longer on a team, but I would encourage everyone to do the above analysis. You will be shocked at how much more stable it makes the system. Well worth the added design complexity.