Minimising jerk by publishing faster than subscribing

asked 2018-01-23 09:07:32 -0500

Alsing
27 ●10 ●12 ●17

Is there a way I could publish a node at a different rate of subscribing?

I do intend to have a python script instercept /cmd_vel and publish it 5 times faster in incrementally.

For eg:

pub = rospy.Publisher("/cmd_vel", Twist)
rospy.SUbscriber("/pre_cmd_vel")
i = 1
rate = rospy.Rate(10)
while linear.change < 5:
    rate = rospy.Rate(50)    
    p.linear.x = i
    pub.publish(p)
    i = i + 1
    rate.sleep()
rate = rospy.Rate(10)`

Would something like that work? SInce jerking is caused by acceleration, breaking a command for a sudden jump in velocity into smaller blocks would give less jerk?

answered 2018-01-23 09:34:05 -0500

gvdhoorn
86574 ●283 ●1432 ●1054 http://cor.tudelft.nl/

Would wiki/yocs_velocity_smoother not do what you want?

As to your question: of course you can 'publish faster than you subscribe' (more accurate would be: publish faster than the rate at which messages are incoming). Just use a timer to control the publication rate.

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Thanks for the recommendation!

I'll take a look at it. HOwever, is my implementation correct?

Alsing ( 2018-01-23 22:31:05 -0500 )edit

Well, no:

Rate inside while
no callback for your subscriber

and some other things.

I would really recommend using the velocity smoother. If you must create something yourself: use a timer, not a while loop.

And I don't understand the p.linear.x = i line.

gvdhoorn ( 2018-01-24 02:52:18 -0500 )edit

@gvdhoorn The crux of the code would be having rate inside while. So while [condition], rate is different. But I looked at the timer and probably will go with that route. Or yocs_velocity_smoother. Thanks alot!

Alsing ( 2018-01-24 04:29:21 -0500 )edit

I don't think Rate works like you think it does: it's a convenience object, that keeps track of time for you between calls to sleep(). It doesn't affect scheduling of your while loop or something. Creating multiple Rate instances at different lines will not do anything special.

gvdhoorn ( 2018-01-24 04:31:03 -0500 )edit

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