# Installing VOXL IO on Sentinel Drone – QUP2 and QUP7 Conflicts

Source: https://forum.modalai.com/topic/4580/installing-voxl-io-on-sentinel-drone-qup2-and-qup7-conflicts
Category: Development Drones (https://forum.modalai.com/category/44/development-drones)
Tags: sentinel
Posted: 2025-07-09 17:02:20 UTC by tonygurney
Replies: 13 · Views: 2541

## tonygurney · 2025-07-09 17:02:20 UTC

Hello ModalAI Team,

I was wondering if you have a specific guide or documentation on how to install the VOXL IO on the Sentinel drone. I’ve run into a couple of issues regarding available QUP ports:

The QUP2 port (J18) is currently occupied by the ESC.

The QUP7 (J16) port has its RX line already in use by the receiver for my remote controller. Pin 11 is already being used.

Given this setup, am I expected to remove the ESC and rewire the motors to the VOXL IO? Or is there an alternate recommended configuration for integrating the VOXL IO on the Sentinel platform?

Any guidance or examples you could provide would be greatly appreciated.

## Reply by Eric Katzfey (ModalAI staff) · 2025-07-09 17:26:52 UTC

@tonygurney What are you trying to use the VOXL 2 IO board for?

## Reply by tonygurney · 2025-07-09 17:27:50 UTC (in reply to Eric Katzfey)

@Eric-Katzfey I am looking to attach a gripper to the drone

## Reply by tonygurney · 2025-07-09 17:35:31 UTC (in reply to tonygurney)

@tonygurney I am also using a ghost atto as my receiver

## Reply by Eric Katzfey (ModalAI staff) · 2025-07-09 17:45:09 UTC (in reply to tonygurney)

@tonygurney Did you want to control the gripper using an application on Linux? Or as a driver in PX4?

## Reply by tonygurney · 2025-07-09 17:54:25 UTC (in reply to Eric Katzfey)

@Eric-Katzfey I’m trying to control the gripper using a Python script running in a Docker container on Linux. My plan is to use pymavlink to listen for remote controller commands, like a specific channel input, and then trigger the gripper based on that input. So I think it's not integrated directly as a PX4 driver; it’s more of a companion application running alongside PX4 that reacts to MAVLink messages in real time.

## Reply by Eric Katzfey (ModalAI staff) · 2025-07-10 16:42:53 UTC (in reply to tonygurney)

@tonygurney One option is to use the ESC board. It has PWM outputs. There is a `voxl-send-esc-pwm-cmd` utility on your VOXL 2 that can be used to send PWM commands to the ESC. However, with this option you would need to solder the PWM connections directly to the ESC board and not everyone is comfortable with that.

## Reply by tonygurney · 2025-07-11 12:44:26 UTC (in reply to Eric Katzfey)

@Eric-Katzfey Correct me if I am wrong, but doesn't the ESC only have enough motor outputs for each of the propellers? So to add another PWM signal I need to either use a GPIO pin or the expansion voxl2 IO board

## Reply by Eric Katzfey (ModalAI staff) · 2025-07-11 16:09:19 UTC (in reply to tonygurney)

@tonygurney The ESC doesn't use PWM to control the motors. So it has the PWM channels free for other uses. The ESC used in the Sentinel actually has the PWM IO on a connector (J3) so no need to solder: https://docs.modalai.com/modal-esc-datasheet/

## Reply by tonygurney · 2025-07-11 20:09:14 UTC (in reply to Eric Katzfey)

@Eric-Katzfey How can I control those PWM signals? Since at the moment I am not reading anything from any of the pins.

## Reply by Eric Katzfey (ModalAI staff) · 2025-07-11 23:43:11 UTC (in reply to tonygurney)

@tonygurney Try the test application `voxl-send-esc-pwm-cmd`. Source code is here: https://gitlab.com/voxl-public/voxl-sdk/services/voxl-io-server/-/blob/dev/tools/voxl-send-esc-pwm-cmd.c?ref_type=heads

## Reply by tonygurney · 2025-07-15 17:09:52 UTC (in reply to Eric Katzfey)

@Eric-Katzfey Thank you I got this helped a lot! I was able to get it working with root access!

## Reply by tonygurney · 2025-07-18 15:42:31 UTC (in reply to Eric Katzfey)

@Eric-Katzfey when using the voxl-send-esc-pwm-cmd do you know how I would be able to trigger the VREF Pin on the ESC 4-in-1? 

I have tried running:

> sudo voxl-send-esc-pwm-cmd -p 12 -w 2201
> sudo voxl-send-esc-pwm-cmd -p 11 -w 2000

and when I measure the voltage from that wire I get ~0.01V which I presume to be noise. 

Is there something that I am missing?  

I am looking to produce a 5V Rail.

## Reply by Alex Kushleyev (ModalAI staff) · 2025-07-21 14:16:00 UTC (in reply to tonygurney)

@tonygurney , I am assuming that you are using the ESC hardware version M0134 (you can confirm using `voxl-esc scan` tool.

Here is the datasheet for M0134.
https://docs.modalai.com/modal-esc-datasheet/

This ESC has an option (via installing a 0 ohm resistor) to provide 3.3V to pin 1 of J3. This is the same voltage that is used for the MCUs that run on the ESC and should be used with caution (if this voltage rail is brought down by overloading, the ESC will shut down). Please see image below that shows where 0 ohm resistor should be (carefully) installed to enable 3.3V on pin1 of J3 (marked in red)

![m0134-diagram.jpg](https://forum.modalai.com/assets/uploads/files/1753107113526-m0134-diagram.jpg) 

If you actually wanted 5V (VAUX), that is available on the other side of the board via two test points at the edge of the board. This voltage rail is provided by a separate switching regulator. See the following section : https://docs.modalai.com/modal-esc-datasheet/#neopixel-led-support

If you REALLY need 5V to be present on pin1 of J3, then you can add a small wire jumper from the VAUX test point directly to the pin1 of J3 (which is marked with a white dot). This pin 1 of J3 is normally disconnected. Please only do this if you are comfortable performing this type of soldering and we cannot guarantee the results :).

Alex