how to calculate quadroped stability

[US Ajayvignesh]

I am doing a 4 legged robot for my project and I need to determine the stability of the robot while walking... the gaiting mechanism has been proposed and I am unsure of how to start the calculations....  Can someone help me out... Should I  find the ZMP(zero moment point) and COG(centre of gravity.... Can someone give me a clear Idea to start with the calculations??



admin edit: changed the subject line from 'Need help' to something more informative

[US Ajayvignesh]

I am doing a Hybird spherical robot which has to walk and roll... For the walking we have chosen a 4 legs so that... the weight falls within our 5 kg limit.... our walking speed should be 0.15m/s..... and I also need help with the material selection... what all factors should I take into consideration to select the appropriate material for the robot...I am looking at HDPE,Aluminium,Steel though mainly plastics.... I will try and upload the picture of our robot.. within a day or two.. please help me..

[Admin]

Should I  find the ZMP(zero moment point) and COG(centre of gravity..

Yeap, this is how to determine *static* stability. It will be statically stable if suddenly all the motors freeze and the bot still doesn't fall over.

http://www.societyofrobots.com/mechanics_statics.shtml


But if your robot will be running, you would need to determine if its *dynamically* stable. Most people write basic simulators for this, as its much easier. I'm sure after a search you'll find some code. There isn't any simple equations because robots can have any feedback PID you want . . .

[US Ajayvignesh]

this is how or robot looks when it rolls....

[US Ajayvignesh]

Can you gimme more inputs on static stability... and I checked with the SoR websites on materials...... But I aint able to come to a clear conclusion.. I mean what all factors should I take into account for choosing the material...I felt aluminium is a good choice as it is lighter and at the same time stronger.... But what if we use plastics...Should I do a FEA on this??

[Admin]

First step whenever doing a mechanical analysis is drawing a Free Body Diagram. Start with that, labeling all the force vectors and lengths of anything of concern.

For material selection, google around for 'stress analysis' and 'calculating beam bending'.

You won't need FEA.

[US Ajayvignesh]

and for the simulation... I found yobotics simulation set.. but it aint working properly... can u suggest if theres some other simulator

[Admin]

I haven't yet found a good simulator . . . search the forum, you'll find links to a few simulators . . .