Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

servo motor pulse width

Status
Not open for further replies.

tinto

Junior Member level 2
Joined
Mar 23, 2011
Messages
21
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Kerala, India
Activity points
1,413
what should be the minimum delay between two successive pulses given to a servo motor? Or, what should be the maximum duty cycle of the pulse train given to a servo motor, if the required pulse width to bring the servo motor to middle position is 1.5ms?
 

tinto

Junior Member level 2
Joined
Mar 23, 2011
Messages
21
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Kerala, India
Activity points
1,413
I had referred that. But I am not clear. I need to know the minimum value for t2. How short it can be? Please refer the figure.
 

vikas_verma

Junior Member level 1
Joined
Jun 30, 2010
Messages
19
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,283
Location
Delhi
Activity points
1,393
generally a servo works with t1 around 1 to 2 ms.
and if T= t1 + t2
then T shuld be around 18 to 20 ms.
means a servo requires 50Hz refreshing rate!
 

tinto

Junior Member level 2
Joined
Mar 23, 2011
Messages
21
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Kerala, India
Activity points
1,413
can t2 be small as 5ms? Will servo motor work with higher refreshing rate?
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
47,489
Helped
14,050
Reputation
28,355
Reaction score
12,708
Trophy points
1,393
Location
Bochum, Germany
Activity points
276,162
can t2 be small as 5ms? Will servo motor work with higher refreshing rate?
It depends on the servo design. With some analog servos, the control loop gain may increase, possibly causing instability. Some won't accept the control signal at all, others will. 50 Hz repetition rate is preferred, because all servos can work with it.
 
  • Like
Reactions: tinto

    tinto

    points: 2
    Helpful Answer Positive Rating

jpanhalt

Advanced Member level 3
Joined
Jun 28, 2010
Messages
724
Helped
216
Reputation
442
Reaction score
219
Trophy points
1,323
Activity points
6,964
can t2 be small as 5ms? Will servo motor work with higher refreshing rate?
FvM is absolutely correct and this comment is not meant to disagree. However, using a Microchip MCU, one may have have problems using the built in PWM to drive a hobby servo with a 50Hz refresh rate, depending on your clock speed. I tested some Hitec analog servos a few years ago, and they will work up to a refresh of about 100 to 120 Hz. Above about 140 Hz, they became unstable. For that particular project, I used a higher refresh rate. For other projects, I have just generated the servo PWM by software.

John
 
  • Like
Reactions: tinto and FvM

    FvM

    points: 2
    Helpful Answer Positive Rating

    tinto

    points: 2
    Helpful Answer Positive Rating

vikas_verma

Junior Member level 1
Joined
Jun 30, 2010
Messages
19
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,283
Location
Delhi
Activity points
1,393
Yes FvM is right and i would suggest you to do some practical with servo!
 

tinto

Junior Member level 2
Joined
Mar 23, 2011
Messages
21
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Kerala, India
Activity points
1,413
I did some experiments with my servo (TowerPro SG 5010) by giving 50Hz refresh rate as well as 100Hz. Both works with my servo. If so how can I understand whether my servo is working properly with 100Hz refreshing rate or my servo is neglecting extra pulses? I don't need to spend time giving extra pulses in my program. Will higher refreshing rate increases the power consumption of the servo?
 

jpanhalt

Advanced Member level 3
Joined
Jun 28, 2010
Messages
724
Helped
216
Reputation
442
Reaction score
219
Trophy points
1,323
Activity points
6,964
What are you using to test your servo? That is, is it something like one of the many NE555 clones or a microcontrller? If you can change the repeat rate easily (e.g., with the 555), you could try something like an 80 Hz repeat rate. If it is dropping pulses, then it would be seeing only 40 Hz and its response -- rate of movement -- should be slower. Slowing the repeat rate is one way to slow servos down, but it is not very effective, and there are better ways available now to do that.

You could also go up in repeat rate until it becomes unstable. Let's say that is 140 Hz. Then test at half that rate. If it is stable there, then it probably is not dropping pulses. I suspect it is not dropping pulses.

John
 
  • Like
Reactions: tinto

    tinto

    points: 2
    Helpful Answer Positive Rating

tinto

Junior Member level 2
Joined
Mar 23, 2011
Messages
21
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Kerala, India
Activity points
1,413
I am now using pic microcontroller to give pulses to the servo motor. Let me try giving higher pulse rates too as you said.
 

vikas_verma

Junior Member level 1
Joined
Jun 30, 2010
Messages
19
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,283
Location
Delhi
Activity points
1,393
50Hz refreshing rate is sufficient and power consumption doesn't depend on refreshing rate,actually motor's motion causes it so!
 
  • Like
Reactions: tinto

    tinto

    points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top