Hexapod math :O

[Nikita]

Hey guys, I don't trust my own math too much nowadays, so could you please just have a look and tell me if I've made a mistake? NOT HOMEWORK!

Okay so lets say I have a hexapod robot. 6 legs. Absolute worst case screnario: 3 of them are in air and the other 3 are stretched out to the max. Each of leg has to lift 1 kg. Each leg has 2 servo's on it. If the robot tries to rise while keeping the legs straight, how long can they possibly be?

Diagram:
[img]http://img191.imageshack.us/img191/7876/hexapodcalc.png[/img]
How I understand it: If one-third of a body has a mass of 1kg (1) (including other legs), and if I had servo's that provided a torque of 14 kilogram-force/cm (2) (4), then the first servo would provide 14 kg/cm torque (2), thereby applying 1 kg-force at the distance of 14 cm. The second servo would do the same (4) and the force it applies after 14 cm (5) would be equal to the bot's weight. Ground's reaction force (6) would be the same. Because the servo 2 is active (4) this force would not bend the limb upwards but instead effectively act on the second joint instead (5) and for the same reason that force could be said to also act on the body (6), therefore 14 cm would be short enough for the whole construct not to thumble.

Either that or I am horrible at math and I should beg you to point out the mistake.

I'm planning to buy 21x9$ servo's and build a robot; While 7 kg/cm servo's are powerful enough to lift the bot, I thought that doubling the power would mean that I could mount some sort of tools on the legs and generally the bot would be faster and stronger, though also heavier and more power-hungry.

PS: any clue how to wire 21 servo so that each of them could get 0.5 A from a 6V source?

[LandTurtle]

I did this stuff in the first grade. :eng101:

[koeniginator]

if this isn't homework, what is it?

[ElectricSquid]

EOD bots are better with treads, screw the legs and go with treads.

[Nikita]

It's me wondering how long should I make the legs for my hexapod. Longer means it can run faster, but too long means it won't have enough servo power to move.

Actually I do believe that legs beat threads on extremely uneven terrain. While it certainly would solve alot of problems to just use threads, legs are more flexible.

[Miktor.]

[QUOTE=koeniginator;26566789]if this isn't homework, what is it?[/QUOTE]
A hobby?

[samframpton]

Or a pick up line.

[FlashFireSix]

I entered the thread, I saw complicated shit, I left the thread

[Mezmer]

[QUOTE=FlashFireSix;26567805]I entered the thread, I saw complicated shit, I left the thread[/QUOTE]
But decided to post

[Water Bear]

[QUOTE=FlashFireSix;26567805]I entered the thread, I saw complicated shit, I left the thread[/QUOTE]
[QUOTE=Mezmer;26568014]But decided to post[/QUOTE]

:D dissed you FlashFire....

Errybody [img]http://xworddeb.files.wordpress.com/2010/09/back-to.gif[/img]

[Bubz]

This thread makes me feel retarded.

Math does too.

I am retarded.

[Cherry Gmod]

Wire it in series, so you have power+ to resistor to servo to power negative. I'm assuming you would want this remote controlled as well?

[Superstormj]

Oh fuck this shit.

[A Wet Towel]

Oh god. This confused me.

[rakkar]

[QUOTE=Yahnich;26569983]You'd need a resistance of 12 ohm to get 0.5A out of 6V.

To get 12 ohm, I guess you'd need to make a resistor with about 360m of copper wire, assuming you use 26 gauge copper wire (0.016 inch thickness). Or you could use carbon, and then you'd need about 1 meter of carbon (26 gauge too)[/QUOTE]

Or maybe you could just buy a resistor...