Mechanics and Construction > Mechanics and Construction

Calculating Stability

<< < (2/2)

Robotboy86:
To be honest the math is kinda ridicilious and I don't remeber it..  your BEST bet though is to make the base dynamic.   Using momentum monitoring(check robotshop.ca for acceloeramators) to determine if it is tilting.. and if it is, then move in the same direction as the tilt.

Otherwise, your base would have to HUGE as hell and heavy to be super stable.

hazzer123:
To do this i would -

Calculate how far up the centre of mass from the floor:

Σmx/Σm = [30 * (6.25 + 48) + M * 6.25] / [30 + M]    M = mass at the base
            = [1627.5 + 6.25M] / [30 + M]

Calculate how far I would have to tip this to get the centre of mass so that it isnt over the base (tipping point) i have assumed that all the mass is spread evenly.

tan(θ) = opp/adj = 9 / [Σmx/Σm]
         = [270 + 9M] / [1627.5 + 6.25M]

θ = tan-1([270 + 9M] / [1627.5 + 6.25M])


Substitute different base mass values into M to get the angle in which your robot could be tipped before toppling over.

eg - no base mass - angle = 9.41 degrees
      10lb base mass - angle = 12.03 degrees

I dont have much time to explain it sorry! :)

Admin:
Actually its more complicated than this.

The above stuff handles what is called static stability. That means if your robot isnt moving, will it tip over? Its like standing on one leg and balancing. Or a car just sitting there not moving (or without flipping over with the engine off).

However what you really want is called dynamic stability. This is like running and not falling over. This is also like a car making a sharp turn on a bend in the road without tipping over.

Its a bit hard to calculate and Im too lazy to derive the equations right now, but it involves momentum about the center of mass as well as robot acceleration rates.

Intuitively you want to do this:

* Wide base
* center of mass as close to the ground as possible
* low acceleration rates
One reason it may be hard to calculate is that you may have trouble finding the center of mass of your robot, or you may have some crazy shapped robot. To compensate, after building your robot, just run tests varying acceleration to tweak it until it doesnt flip over.

This is also why I always tell people to keep the batteries at the very bottom of their robots - for dynamic stability.

(hope that helps)

Navigation

[0] Message Index

[*] Previous page