Gym exercise equipment analysis

AI Thread Summary
The discussion focuses on analyzing the forces exerted on a leg extension machine's workarm, specifically with a maximum load of 300 pounds from the weight stack. The user is calculating torque on the cam and analyzing the mechanical structure, considering the forces acting on various components, including the cam, rotating bearing, and lever. They have computed torque values for the cam and bearing but are uncertain about how to determine the forces on the final beam where the user's leg applies force. The conversation emphasizes the need to clarify whether to analyze the system as a whole or in parts, with an interest in understanding the reaction forces involved. The user seeks confirmation on their calculations and approach to ensure accuracy in their analysis.
JasmineRM
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I need some help on the direction to go with this problem. This is a workarm on a leg extension machine and there's 300 pounds (max) coming from the weight stack attached via a cable on the cam. I need to find the total force exterted on this system to double check my results on an analysis.

To explain the diagram a littler more, there's a cam that exerts a torque onto the shaft connected to it. Then there's a perpendicular lever connected to that where the leg extension pad is connected perpendicular to that. I know there's a force exerted on to the work arm from a person seated using the machine.

I know for sure I can calculate the torque on the cam using distances from the cable as different degrees to the pivot point and multiplying that by the 300 lbs. I am lost on how to approach the rest. Should I analyze part by part or as a whole system? Any input would be great because I've racked my head on this for quite some time and I am stuck. Thank you

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Are you trying to find the Force by the user's leg (as a function of angle), or the reaction Forces applied to the shaft by the bearings?
that is, are you analyzing the biology/kinesiology, or the mechanical machine structure?
 
lightgrav said:
Are you trying to find the Force by the user's leg (as a function of angle), or the reaction Forces applied to the shaft by the bearings?
that is, are you analyzing the biology/kinesiology, or the mechanical machine structure?
The mechanical machine structure
 
Would this be the correct thinking...
I analyzed each part separately. For the cam, I took the distance from the cable to the center and found the max torque to be 2435.4 lb*in. Then for the rotating bearing, I used T = F*d, with the force being 300 lb and distance as the length of the bearing, getting 1912.5 lb*in. For the lever, I used the cantilever beam equation and 3750 lb*in. As for the final beam which is where the leg has a force going up on ...I was unsure of how to go about the forces on this one. I have two reaction forces, one in the x and one in the y which equals 300lb, weight going down, another weight of a person going down because there's a potential someone could sit in the end of this beam (although hopefully unlikely) that is at max 300 lb(weight stack weight), and the questionable force going up that I am trying to find.

Is this correct?


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