# How to make the diagonal legs of the quadruped robot have the same step height when walking?

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Nayla 2023 年 6 月 5 日

Hi there,
i have another concern regarding the robot modelling of a quadruped robot. How can I get the attached multibody robot models legs liflt at the same rate while its walking. Fact is when running the simulation it can be observed that the diagonal legs are not lifting up the same way as they should (for example, the rear right leg is not lifting as high as the front left leg).
Why are the step heights in the simulation so different even though the values were set the same? How do I get a homogenous step height for all the diagonal legs during the entire simulation?

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### 回答 (1 件)

Nathan Hardenberg 2023 年 6 月 5 日
For me it looks like the legs are moving the same! But what happens, is that the robotdog tilts. Thats why the front legs are farther from the ground. The back legs do not really leave the ground at all. Lifting two legs at the same time results in an unstable position thus resulting in the tiliting movement.
There are two ways to resolve that issue:
• Implement dynamic walking. This is when the legs move so fast that the model can't tilt as fast and the robotdog can balance on two legs for a short period of time (very simplified). This is very hard to do right! Just moving the legs faster could work but is normally not dynamic walking.
• Implement better static waking. This is when the robot has always 3 contact points with the ground, and the center of mass is in the middle of them. This is easier but still no trivial task. You would most likely also need to change your shoulder joints to be able to move the center of mass to the desired position. I recommend checking out this and the following videos from James Bruton on Youtube regarding this topic: https://youtu.be/TmY8CwuATiU

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