# Control robot arm with on / off button

**URL:** <https://discourse.nodered.org/t/control-robot-arm-with-on-off-button/18213>\
**Category:** General\
**Created:** [21 November 2019 01:54 UTC](https://discourse.nodered.org/t/control-robot-arm-with-on-off-button/18213 "2019-11-21T01:54:29Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![Suave](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@Suave](https://discourse.nodered.org/u/Suave)\
**Post date:** [21 November 2019 01:54 UTC](https://discourse.nodered.org/t/control-robot-arm-with-on-off-button/18213/1 "2019-11-21T01:54:29Z")

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I have a robot arm with 4 servos and I want to use an on / off button to start a process. I found several examples of flows where they use a slide bar to individually control each servo. My question is can I use a button to start the process until I turn off that button?

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**Author:** ![craigcurtin](https://avatars.discourse-cdn.com/v4/letter/c/94ad74/32.png) [@craigcurtin](https://discourse.nodered.org/u/craigcurtin)\
**Post date:** [21 November 2019 03:52 UTC](https://discourse.nodered.org/t/control-robot-arm-with-on-off-button/18213/2 "2019-11-21T03:52:59Z")

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How does the robot talk to the NR controller ?

Create a dashboard page, insert a Button, have it send a command on a MQTT topic.

In your Flow - monitor that topic and then send out the commands to the 4 servos on other MQTT topics

Have a 2nd button on the dashboard that does the opposite to stop the robot

This all assume of course that your robot is able to be spoken to by MQTT

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**Author:** ![Suave](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@Suave](https://discourse.nodered.org/u/Suave)\
**Post date:** [22 November 2019 03:00 UTC](https://discourse.nodered.org/t/control-robot-arm-with-on-off-button/18213/3 "2019-11-22T03:00:42Z")

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Thanks I will try that.  
I am using an Esp8266, MQTT and Node-RED.  
Another question, I have to put an MQTT theme for each servo even if it is a single process but that includes each servo separately?

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**Author:** ![craigcurtin](https://avatars.discourse-cdn.com/v4/letter/c/94ad74/32.png) [@craigcurtin](https://discourse.nodered.org/u/craigcurtin)\
**Post date:** [25 November 2019 02:39 UTC](https://discourse.nodered.org/t/control-robot-arm-with-on-off-button/18213/4 "2019-11-25T02:39:23Z")

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No you could have a single MQTT topic and have your code on the ESP8266 turn off/on all the servos at one depending on what you receive

Are you writing your own code for the ESP8266 or using one of the prebuilt firmwares ?

Depending on what level of PMW/Stepping you are trying to do on the ESP8266 i do not think you will be able to control 4 servos

It may be worthwhile looking at a dedicated servo controller/board that connects to the ESP8266

Craig

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**Author:** ![dynamicdave](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/dynamicdave/32/96_2.png) [@dynamicdave](https://discourse.nodered.org/u/dynamicdave)\
**Post date:** [25 November 2019 07:16 UTC](https://discourse.nodered.org/t/control-robot-arm-with-on-off-button/18213/5 "2019-11-25T07:16:45Z")

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I've used this servo controller board with a Wemos D1 Mini (ESP8266) flashed with ESP-Easy.

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The basic PWM function (using ESP Easy) is limited to controlling two servos, so this external board gets over that limitation. There are drivers on the 'Devices' tab (within ESP-Easy) so implementation should be simple.

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**Author:** ![Suave](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@Suave](https://discourse.nodered.org/u/Suave)\
**Post date:** [25 November 2019 21:01 UTC](https://discourse.nodered.org/t/control-robot-arm-with-on-off-button/18213/6 "2019-11-25T21:01:34Z")

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The arduino code I am doing based on some examples but using the slider and the original code of MQTT\_esp8266, what I am trying to do is that when the switch button receives a 1 it starts the process of the robot arm and when it is a 0 it stops.

I decided to do it this way because I could do it with Blynk, but this is just the beginning of my programming, then I went to add sensors and other motors, and the blynk no longer supported me for that.

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**Author:** ![craigcurtin](https://avatars.discourse-cdn.com/v4/letter/c/94ad74/32.png) [@craigcurtin](https://discourse.nodered.org/u/craigcurtin)\
**Post date:** [25 November 2019 23:04 UTC](https://discourse.nodered.org/t/control-robot-arm-with-on-off-button/18213/7 "2019-11-25T23:04:02Z")

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As Dave has said above - go to a precompiled image (EspEasy) and use the board above (presuming that it is adequate for the servos you are driving)

Craig