# publishing joint trajectory msgs on gazebo

hello i have a delta robot that is controlled using joint trajectory. i created 1 publisher for the inverse kinematics and a subscriber to receiive the result . i want those result to be published on gazebo directly. i am facing those problems:

```
[ERROR] [1557254010.564552520, 268.353000000]: Exception thrown when deserializing message of length [104] from [/inverse_sub]: Buffer Overrun
[ERROR] [1557254010.565049509, 268.353000000]: Exception thrown when deserializing message of length [16] from [/inverse_sub]: Buffer Overrun
[ERROR] [1557254010.565280432, 268.353000000]: Exception thrown when deserializing message of length [8] from [/inverse_sub]: Buffer Overrun
```

the following is my subscriber.py file :

```
#!/usr/bin/env python
import rospy
from std_msgs.msg import Float64MultiArray
from std_msgs.msg import Time
from std_msgs.msg import Header
from std_msgs.msg import Duration
import numpy as np
from math import *
import time
from matplotlib.pyplot import *
from trajectory_msgs.msg import JointTrajectory
from trajectory_msgs.msg import JointTrajectoryPoint
sqrt3 = sqrt(3)
sin120 = sqrt(3) / 2
cos120 = -0.5
tan60 = sqrt(3)
sin30 = 0.5
tan30 = 1 / sqrt(3)
default_drob_dimensions = {'R':0.40941, 'r':0.4, 'l':0.8, 'd':0.07845}
c_default_drob_dimensions = {'R':0.40941, 'r':0.4, 'l':0.8, 'd':0.07845}
a = 0
b = 0
c = 0
secs = 0
nsecs = 1
def s_inv_kinematics(x0, y0, z0, drob_dimensions = default_drob_dimensions):
"""
Takes the position of the end effector as input and returns
the corresponding angle in degree if existing
else it returns "position does not exist"
"""
# Robot dimensions
d = drob_dimensions['d']
R = drob_dimensions['R']
r = drob_dimensions['r']
l = drob_dimensions['l']
e = 2 * sqrt(3) * d
f = 2 * sqrt(3) * R
re = l
rf = r
y1 = -0.5 * 0.57735 * f
y0 -= 0.5 * 0.57735 * e
a = (x0 * x0 + y0 * y0 + z0 * z0 + rf * rf - re * re - y1 * y1) / (2 * z0)
b = (y1 - y0) / z0
d = -(a + b * y1) * (a + b * y1) + rf * (b * b * rf + rf)
if (d < 0):
return "position does not exist"
yj = (y1 - a * b - sqrt(d)) / (b * b + 1)
zj = a + b * yj
if (yj > y1):
toadd = 180
else:
toadd = 0
theta = 180 * atan(-zj / (y1 - yj)) / pi + toadd
return theta
def inv_kinematics(x0, y0, z0, drob_dimensions = default_drob_dimensions):
"""
Takes the position of the end effector as input and returns
the 3 angles in degree if existing
else it returns "position does not exist"
"""
# Robot dimensions
d = drob_dimensions['d']
R = drob_dimensions['R']
r = drob_dimensions['r']
l = drob_dimensions['l']
e = 2 * sqrt(3) * d
f = 2 * sqrt(3) * R
re = l
rf = r
theta1 = s_inv_kinematics(x0, y0, z0, drob_dimensions)
theta2 = s_inv_kinematics(x0 * cos120 + y0 * sin120, y0 * cos120 - x0 * sin120, z0, drob_dimensions)
theta3 = s_inv_kinematics(x0 * cos120 - y0 * sin120, y0 * cos120 + x0 * sin120, z0, drob_dimensions)
if (
theta1 == "position does not exist" or theta2 == "position does not exist" or theta3 == "position does not exist"):
print ("position does not exist")
print (theta1, theta2, theta3)
theta1 *= 3.14/180
theta2 *= 3.14/180
theta3 *= 3.14/180
a = theta1
b = theta2
c = theta3
pub1 = rospy.Publisher ("/delta_robot/delta_robot_controller/command", JointTrajectory, queue_size=10)
pub2 = rospy.Publisher ("/delta_robot/delta_robot_controller/command", JointTrajectoryPoint, queue_size=10 ...
```

Why are you creating 5 different publishers for the single action server

`/delta_robot/delta_robot_controller/command`

?because i am sending a joint trajectory that requires all those data and each data has a type of message. am i doing wrong? do you have a solution or an example that can help me?

that's not how things work. You don't have to create publishers for each field separately. Just create a single one per message.

But in this case, you'll want to actionlib and the Python Simple Action client, as that

`/delta_robot/delta_robot_controller`

actually exposes a`FollowJointTrajectory`

action server and you need to write a client for it.