# Thread: HELP legged robot torque math

1. lutinplunder Relay Join Date
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## HELP legged robot torque math

I am trying to modify Ferret's Quad Torque spreadsheet to work with hex and octopods. The first problem I am running into when calculating N1 & N2. The numbers I am getting don't look right to me and I am not sure where my mistake is. If I understand the forces/math involved, for a hex N1=2*N2 and an octo should be N1=N2 since you have the same number of legs in contact with the ground on each side.

I am hoping those of you with more experience can help me figure it out.

Legged Robot Torques.zip  Reply With Quote

2. lutinplunder Relay Join Date
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## Re: HELP legged robot torque math

I found one of the major errors in my N2 formula for the hex so now if my above logic is correct I'm within 0.5 (N2 high) for the hexapod and 1.96 (N1 high) for the octopod.

Legged Robot Torques v2.zip
Last edited by lutinplunder; 3 Weeks Ago at 07:07 PM.  Reply With Quote

3. lutinplunder Relay Join Date
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## Re: HELP legged robot torque math

Solved the equation for the octopod, I needed to reconfigure equation to be 2*N1=2*N2. I had originally thought that simplifying to N1=N2 would work... odd.  Reply With Quote

4. lutinplunder Relay Join Date
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## Re: HELP legged robot torque math

Still haven't figured out the Hexapod calculation for N2 Here's what I've got so far...

Calculations extended from those found at the RobotShop website and based on Ferret's original Spreadsheet.

Leg section masses are taken to be actuator weights plus leg weights
N1,2: normal (reaction) forces
L1,2,3,4,5: Lengths of leg sections and half body width
W1,2,3,4: Weights of actuators at each joint
M1,2,3,4: Weights of leg segments
WBody: Weight acting at center of mass
T1,2,3,4: Torques required at Tars/Tibia, Tibia/Femur, Femur/Coxa, Coxa/Body joints respectively. (+) is counter clockwise, (-) is clockwise

Wbody = Wcomplete chassis
WIncline = WTotal(Sin(incline angle))

N1+2*N2=Wbody+(#LegsUp)(W1+W2+W3+W4+Wn+M1+M2+M3+M4+Mn)

To simplify and reduce equation lengths;
L1.cos(a)=A, L2.cos(b)=B, L3.cos(o)=C

N2=2*(W1+M1)(A+2(B+C+L4+L5))+2*(W2+M2)(A+B+2(C+L4+ L5))+2*(W3+M3)(A+B+C+2(L4+L5))+2*(W4+M4)(A+B+C+L4+ 2 .L5)+(Wbody+(#LegsUp)(W1+Wn+M1+Mn))*(A+B+C+L4+L5)+ (W4+M4)(A+B+C+L4)+(W3+M3)(A+B+C)+(W2+M2)(A+B)+(W1+ M1) A/4(A+B+C+L4+L5)  Reply With Quote