Mechanics and Construction > Mechanics and Construction
building a bi-ped - tension calculator
TrickyNekro:
Greetings to everybody!!!
Lately I'm trying to materialize my new idea to build a biped robot (walker)
I know programming will be tough and building the case even more difficult but I have somethings that I need to work out...
First of all I'll be using some (10 by number) HS - 311 from hitec at 49 oz/in @ 6V
Considering I'll apply 7.2Volts to the servos (which is a max rated value) and building a extremely lightweight robot is this torque enough???
Probably my source of power will be some cell phone Li-po so same samples I've got will do, from Dallas!!!
And the case will be made out of plastic (or steel sheets at worst occasions)...
So the weight probably won't be over 1kilo or 2.2 libs (if I'm right!!!)
I came to the conclusion I need a tension calculator and any suggestions available for building a case (not the right forum I know)
But most important to me is the calculator!!!!
So if anyone knows the math or a Java program I 'd like it very very much!!!!
With best regards,
Tricky Nekro, Greece
Admin:
Tension is calculating the stretching of something. Like if you pull a rubber band, you'd use a tension calculator to determine how far it stretches.
What you want is a statics calculator, more specifically a moment arm (torque) calculation of the knees.
Here is what you do. Draw your robot as a stick figure, with the robot is a sitting position, knees bent at 90 degrees. This position requires more servo torque (in the knee servo) than any other position.
The torque is simply robot_weight * thigh_length. Thigh_length being the distance from the knee to the hip of the robot, and robot_weight being the weight of everything on the robot above the knee.
You might want to consider using lighter/smaller micro servos (that also cost ~$10) for the arms and head to reduce robot_weight.
Oh and if you use a double knee design (makes legs faster), then both servos need the same torque you calculated earlier (they dont add unfortunately).
One day I'll make a biped calculator for SoR . . .
TrickyNekro:
Thanks for the reply!!! I'll be able work with that!!!
I'm not planning to use any head or hands! I'm olny planning building a walking platform!!!
Thanks again,
Best Regards, Tricky Nekro
Admin:
just an FYI, some people put arms on their bipeds solely to improve weight shifting and balancing
(for example, run around your room and notice what your arms do)
TrickyNekro:
I know, but I just don't have the money to buy more servos...
I have been trying to walk as a robot days now to understand the weight balancing and the movements needed to be done!!!
BTW do you know , or anybody else, how to build the joints for the legs. I mean that in order to make a stable joint you need at least two points grabbed together... I one is the servo horn, how can I build the other... (It's tough finding any links in google since I don't know what to type!!!)
Thanks for the reply again,
Best regards,
Tricky Nekro, Greece
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