您如何在Pymunk中实现“伺服”关节？
我正在尝试创建一个简单的模型，其中一个盒子在它下面的一条细“腿”上保持平衡。我已经能够创建一个盒子并使用PinJoint将其连接到地面，但是似乎没有任何方法可以控制连接到盒子的角度。我希望能够指定附着角度。其他关节似乎都不支持这一点。除了SimpleMotor关节外，它们似乎都是被动关节，但即使如此，这也只是您无法控制的恒定旋转关节。
通过使用PinJoint在两端将两个薄盒以及一个SimpleMotor附加在一起，我设法将一些东西拼凑在一起，以响应用户按下“上”和“下”来使它们相对旋转“ 方向键。下面是代码：
import sys
import pygame
from pygame.locals import USEREVENT, QUIT, KEYDOWN, KEYUP, K_s, K_r, K_q, K_ESCAPE, K_UP, K_DOWN
from pygame.color import THECOLORS
import pymunk
from pymunk import Vec2d
import pymunk.pygame_util
class Simulator(object):
def __init__(self):
self.display_flags = 0
self.display_size = (600, 600)
self.space = pymunk.Space()
self.space.gravity = (0.0, -1900.0)
self.space.damping = 0.999 # to prevent it from blowing up.
# Pymunk physics coordinates start from the lower right-hand corner of the screen.
self.ground_y = 100
ground = pymunk.Segment(self.space.static_body, (5, self.ground_y), (595, self.ground_y), 1.0)
ground.friction = 1.0
self.space.add(ground)
self.screen = None
self.draw_options = None
def reset_bodies(self):
for body in self.space.bodies:
if not hasattr(body, 'start_position'):
continue
body.position = Vec2d(body.start_position)
body.force = 0, 0
body.torque = 0
body.velocity = 0, 0
body.angular_velocity = 0
body.angle = body.start_angle
def draw(self):
### Clear the screen
self.screen.fill(THECOLORS["white"])
### Draw space
self.space.debug_draw(self.draw_options)
### All done, lets flip the display
pygame.display.flip()
def main(self):
pygame.init()
self.screen = pygame.display.set_mode(self.display_size, self.display_flags)
width, height = self.screen.get_size()
self.draw_options = pymunk.pygame_util.DrawOptions(self.screen)
def to_pygame(p):
"""Small hack to convert pymunk to pygame coordinates"""
return int(p.x), int(-p.y+height)
def from_pygame(p):
return to_pygame(p)
clock = pygame.time.Clock()
running = True
font = pygame.font.Font(None, 16)
# Create the torso box.
box_width = 50
box_height = 100
leg_length = 100
mass = 1
points = [(-100, -1), (0, -1), (0, 1), (-100, 1)]
moment = pymunk.moment_for_poly(mass, points)
body1 = pymunk.Body(mass, moment)
# body1.position = (0, 0)
body1.position = (self.display_size[0]/2, self.ground_y+100)
body1.start_position = Vec2d(body1.position)
body1.start_angle = body1.angle
shape1 = pymunk.Poly(body1, points)
shape1.friction = 0.8
self.space.add(body1, shape1)
# Create bar 2 extending from the right to the origin.
mass = 1
points = [(100, -1), (0, -1), (0, 1), (100, 1)]
moment = pymunk.moment_for_poly(mass, points)
body2 = pymunk.Body(mass, moment)
# body2.position = (0, 0)
body2.position = (self.display_size[0]/2, self.ground_y+100)
body2.start_position = Vec2d(body2.position)
body2.start_angle = body2.angle
shape2 = pymunk.Poly(body2, points)
shape2.friction = 0.8
self.space.add(body2, shape2)
# Link bars together at end.
pj = pymunk.PinJoint(body1, body2, (0, 0), (0, 0))
self.space.add(pj)
motor_joint = pymunk.SimpleMotor(body1, body2, 0)
self.space.add(motor_joint)
pygame.time.set_timer(USEREVENT+1, 70000) # apply force
pygame.time.set_timer(USEREVENT+2, 120000) # reset
pygame.event.post(pygame.event.Event(USEREVENT+1))
pygame.mouse.set_visible(False)
simulate = False
while running:
for event in pygame.event.get():
if event.type == QUIT or (event.type == KEYDOWN and event.key in (K_q, K_ESCAPE)):
#running = False
sys.exit(0)
elif event.type == KEYDOWN and event.key == K_s:
# Start/stop simulation.
simulate = not simulate
elif event.type == KEYDOWN and event.key == K_r:
# Reset.
# simulate = False
self.reset_bodies()
elif event.type == KEYDOWN and event.key == K_UP:
motor_joint.rate = 1
elif event.type == KEYDOWN and event.key == K_DOWN:
motor_joint.rate = -1
elif event.type == KEYUP:
motor_joint.rate = 0
self.draw()
### Update physics
fps = 50
iterations = 25
dt = 1.0/float(fps)/float(iterations)
if simulate:
for x in range(iterations): # 10 iterations to get a more stable simulation
self.space.step(dt)
pygame.display.flip()
clock.tick(fps)
if __name__ == '__main__':
sim = Simulator()
sim.main()
但是，这种行为有些奇怪。当您按向上/向下按钮时，会动态设置SimpleMotor关节上的速度，从而使两个框在其共同的“伺服关节”处旋转，例如：
除了随着时间的推移，这两个杆将翻转到一端，否则将克服重力并看起来像：
为什么是这样？我对Pymunk / Chipmunk物理模拟器还很陌生，所以我不确定我是否正确使用了这些关节。
最佳答案
可能导致问题的几件事：
忽略两个形状之间的碰撞。由于电机和销接头将它们压在一起，但是碰撞解决方案将它们推开，可能会发生奇怪的事情。您可以通过将两个形状设置为同一组来实现：shape_filter = pymunk.ShapeFilter(group=1)shape1.filter = shape_filtershape2.filter = shape_filter
这两个形状的重心在其末端，而不是在中心。尝试将其移到中心（[(-50, -1), (50, -1), (50, 1), (-50, 1)]）。
（在这种情况下，我认为1足以解决问题，但在您发现其他奇怪的情况下，我加了2）