如何理解continuous_state向量? [英] How to make sense of the continuous_state vector?

问题描述

我正在尝试平衡移动的倒立摆(即segway).

I am trying to balance a mobile inverted pendulum (i.e. segway).

对于仿真，我创建了一个简单的机器人，该机器人包含一个通过旋转接头连接到圆柱(车轮)上的杆.

For the simulation, I created a simple robot that involves a pole attached to a cylinder (wheel) through a revolute joint.

构造我的MIP工厂后，plant.num_positions()返回8，而plant.num_velocities()返回7，即continuous_state的总大小为15

After constructing my MIP plant, plant.num_positions() returns 8 and plant.num_velocities() returns 7, i.e. the total continuous_state size is 15

1. 我如何理解如此众多的州?
我假设其中之一代表杆与垂直线所成的角度.我怎么找到那个?
2. 还有，为什么num_positions()不等于num_velocities()?

1. How do I make sense of this large number of states?
2. I suppose one of these represents the angle that the pole makes with the vertical. How do I find that?
3. Also, why is num_positions() not equal to num_velocities()?

推荐答案

默认情况下，urdf/sdf解析器为系统添加基于四元数的浮动基数.该浮动基础关节具有7个位置变量(x，y，z +四元数)和6个速度(xdot，ydot，zdot和空间速度).您应该使用多实体API以正确的顺序获取变量.

By default, the urdf/sdf parser adds the system with a quaternion-based floating base. This floating base joint has 7 position variables (x,y,z + quaternion) and 6 velocities (xdot, ydot, zdot, + spatial velocity). You should use the multibody API to get the variable in the right order.

您可以在世界链接和您的基地之间添加接缝(在urdf/sdf或代码中)，以将隐含的浮动接缝替换为例如.底部的棱柱形接头.

You can add a joint between the world link and your base (either in the urdf/sdf or in your code) to replace that implied floating joint with e.g. a prismatic joint at the base.

在drake中有许多如何进行模拟的示例，但在 http://underactuated.mit上也有. edu

There are lots of examples of how to simulate it, in drake, but also at http://underactuated.mit.edu

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