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Calculating Stability

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airman00:
How can I calculate how much weight I need to put on a motorized base in order for the robot to be stable? I intend to put  30 pounds on the robot but I need those parts to be at least 4 feet above the base.
What is the calculation for  finding out how much weight I need on the bottom so that the weight on top doesn't cause the robot to tip over?
 My base is 18" by 18" with 12.5" wheels. The base can move a maximum of 250 lbs.
 
Please help.

Robotboy86:
Torque my friend :)

If you have 30 lbs on top of the robot, 4 feet above the base.. they can exert 4ft*30lbs of torque onto the base.. of 120ft/lbs of torque.  Is 120ft/lbs enough to move your base of 250lbs?

airman00:
But did you take into account the fact that the base is on wheels?

Does that equation add up with more than one object? If i have object that is 20lbs at 2 ft and object that is 30 lbs at 4 ft, do i do 40 + 120 and then figure it out?

Robotboy86:

BEFORE YOU READ THIS!  Remeber, its been 3 years since i've taken physics lol.

The fact that is on wheels DOES factor in, but in your favor.

As far as the weight distrubition it does change several factors..

If you have 20lbs at 2 feet, thats 40ft/lbs of torque, along with 120ft/lbs, which is 160ft/lbs.  Now as far as your wheel base,  if you could provide that, along with its weight(and height) we could determine its ability to resist tipping.

Another key factor though is the size of the base.  If the base itself is 4 feet wide, and 250lbs.. then you could literally take the 30lbs and 20lbs load and lean them off the base, and it would not tip over.  The fact that it is on wheels is in your favor, because it would resist tipping, and would move forward.  Infact, this is how modern SUV's avoid roll overs. If it detects that is leaning past X point it will apply brakes to turn the vehicle INTO the fall, and transfer the motion from side to side, to forward motion(where the suv is far less likely to tip).

airman00:
Thanks,
can you please give me the equation and tell me what to fill in. Like say V=IR, tell me that V= volts I= current and R= resistance
If you remember the equations

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