# Help from model and robot making professionals

**URL:** <https://discourse.nodered.org/t/help-from-model-and-robot-making-professionals/40881>\
**Category:** Developing Nodes\
**Created:** [12 February 2021 17:20 UTC](https://discourse.nodered.org/t/help-from-model-and-robot-making-professionals/40881 "2021-02-12T17:20:26Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![iiot2k](https://avatars.discourse-cdn.com/v4/letter/i/8baadc/32.png) [@iiot2k](https://discourse.nodered.org/u/iiot2k)\
**Post date:** [12 February 2021 17:20 UTC](https://discourse.nodered.org/t/help-from-model-and-robot-making-professionals/40881/1 "2021-02-12T17:20:26Z")

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Hi,  
I start to write two nodes for pca9685 pwm chip.  
One node is for normal pwm output.  
And other one is special for robot and model making hobbist.  
My question is how control the servos on pca9685 output.  
I read on internet, that servos works with pwm frquency 50Hz and pulse between 1 and 2 ms.  
Is this valid for all servos or is there difference between servos ?  
There are Continuous Rotation Servos. How control this servos ?  
Thanks for answers.

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**Author:** ![dceejay](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/dceejay/32/38_2.png) [@dceejay](https://discourse.nodered.org/u/dceejay)\
**Post date:** [12 February 2021 17:58 UTC](https://discourse.nodered.org/t/help-from-model-and-robot-making-professionals/40881/2 "2021-02-12T17:58:52Z")

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Certainly most servos have a centre point at 1.5mS - (but can usually be trimmed (ie moved slightly) so you don't have to adjust manually.). Some servos have hard end stops - and so the max and min must also be adjustable so as not to wreck the gears. Typically they are around 1mS and 2mS for +- 90 degrees... but they all vary - most normally they are within that - but I have seen some go beyond.  
I'm not sure re continuous rotation ones - never used them. It may be just the speed is proportional to the "distance" from 1.5.. but again the centre point may need to be adjustable so that the servo is fully stopped at that point.

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**Author:** ![iiot2k](https://avatars.discourse-cdn.com/v4/letter/i/8baadc/32.png) [@iiot2k](https://discourse.nodered.org/u/iiot2k)\
**Post date:** [12 February 2021 19:17 UTC](https://discourse.nodered.org/t/help-from-model-and-robot-making-professionals/40881/3 "2021-02-12T19:17:43Z")

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Thanks for answer. Its best case to order servos and test it real. 💯

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**Author:** ![Colin](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/colin/32/17040_2.png) [@Colin](https://discourse.nodered.org/u/Colin)\
**Post date:** [12 February 2021 20:59 UTC](https://discourse.nodered.org/t/help-from-model-and-robot-making-professionals/40881/4 "2021-02-12T20:59:26Z")

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> [@iiot2k](#):
>
> There are Continuous Rotation Servos. How control this servos

I think these work from the same pwm signal, but it controls the speed rather than position.

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**Author:** ![iiot2k](https://avatars.discourse-cdn.com/v4/letter/i/8baadc/32.png) [@iiot2k](https://discourse.nodered.org/u/iiot2k)\
**Post date:** [12 February 2021 21:56 UTC](https://discourse.nodered.org/t/help-from-model-and-robot-making-professionals/40881/5 "2021-02-12T21:56:43Z")

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Yes I look in manual:  
1.5ms stops servo.  
0.7ms-1.5ms reverse speed  
1.5ms-2.3ms forward speed.  
Its more for robot application (vacuum cleaner robot).  
I ordered 2 of them for test.  
 ![servo](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/3/c/3cb4b2cb489ca691c25baf8432c2ba6541ab1519.jpeg)

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**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [13 April 2021 21:56 UTC](https://discourse.nodered.org/t/help-from-model-and-robot-making-professionals/40881/6 "2021-04-13T21:56:49Z")

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