Is there a ratio between the coxa, femur and tibia leg segments on a 18 DOF hexapod that people tend to prefer? I was looking for papers and posts on the subject but didn’t see a whole lot. What are the design considerations and tradeoffs that should be considered when choosing these ratios. Speed, stability, clearance height, weight, energy efficiency of locomotion, torque requirements for the joints all come to mind, are there other factors to consider that I haven’t included? Are there general rules of thumb like the tibia should never be greater than 2x the femur? or the femur should generally be longer than the tibia because of x? Are there good resources that discuss this topic that someone could point me to? Thanks so much!
@Gorillapaws Welcome to the RobotShop Community. It sounds like you’re looking to develop a custom hexapod? You have some very interesting timing because Lynxmotion is currently developing the next generation of hexaopds with help from experts in the community:
The mechanical prototype has been created so everyone is working on the same platform, and the dimensions were largely based on those of the previous Lynxmotion SES V1 generation of hexapods:
Although these were developed before my time here, the development threads can still be found on this forum (ex. Phoenix, A-Pod). I suspect that the following criteria played important factors in the dimensions:
- Torque needed at each joint (two in the shoulder, one in the knee)
- Size of the RC servos used which can provide the torque
- In the case of Lynxmotion’s modular Erector Set, the dimensions of existing brackets
This might also help with basic calculations for torque:
However, in terms of optimizing the dimensions for a walking gait, can’t provide you specific articles or information. Sorry.
Zenta’s Phoenix spreadsheet might offer some information: