24v Steering Servo Power and Signal from PM07 board

I’m working on building an autonomous rover out of an electric quad atv. To manage the ackerman steering I’m using a large 24v servo. I just got the Pixhawk4 board in and I’m struggling to understand how to power and provide signal through the PM07 board to this servo. Am I going to have to bypass power direct from the 24v source straight to the servo and use the FMU PMW-OUT connectors on the PM07 to provide the signal or am I missing something. My first thought was to connect the servo to the M2 mount to get power and signal, but wasn’t sure that it would map correctly when I go to configure this as a servo and not a drive motor. Anyone out there dealt with servos that need more power than the +5v?

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So is the pwm signal that the servo uses a 5v signal? It is common to have a 12 or 24v supply and a 5v data (pwm) level.

If it requires a 24v pwm signal (unlikely) then you will have to check that the pwm pins on the flight controller are ok to be fed 24v on the specs.

The PWM signal is a standard signal voltage. Its the voltage supply for the servo that is 24V. Thats what I’m trying to wrap my mind around with the PM07. Lets say I was running a HITEC high torque servo that needs +7v, it can’t pull that from the BEC 5v rail on the PM07, does that mean the power for that servo needs to bypass the PM07 and only the signal is connected through the board and he power comes from a power distribution block or straight from the battery or am I missing something about the PM07 that isn’t documented.

Exactly as you said


Thanks. Thats kind of what I figured. It just wasn’t obvious looking at the board and trying to make sense of how its managing power? This adds another question then? Should I even be pulling power for the 24v brushed motor to the sabertooth from the PM07 as well using the M1 spot or leave that out as well and just route the signal? I get the sense that the PM07 is intended for multirotor setups, but its marked as supporting high current and up to 12s. Are there pros and cons to this setup for rovers?

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Well I hated this fc and it’s pm07 which is humongous. Than you need the power sensor before it, again space. However, power pads on that board are just fine to provide all 6s without any issue though a bit small. You can draw all your 6s requirements from those. Power the Servo rail with 5v and I guess your good to go!?
I see no reason not to power you Servos from power pads and use m1-m8 for your signals.

Your definition of humongous and mine must be drastically different, but considering the vehicle is man sized, space isn’t a problem for me. When you say power sensor A) what power sensor are you referring to and B) before what element the motor controller or power management board?

You can take the 24v directly from battery source, the only con is you won’t be counting the current with fc but that wont matter on a rover with a generator.
All the power board is really giving you is a 5v supply to the fc. And the one supplied with the ph4 is really aimed at a multirotor.
If anyone is doing any other platform than a multirotor they should use a simpler power module with the ph4.
Normally the servo supply with flight controllers is from your own voltage source, ie the esc or from a bec or separate battery for servos.

For your info.
The power module is connected with 2 x 6 wires. They are -,-,volt,current,++ so if you aren’t worried about your remaining battery capacity, you dont need it. Get a small power module that plugs into the same 6 pin cable for easy plug in and your done.
The pwm section (fmu and io) is just fancy labelling and multirotor aimed positioning for 16 pwm outputs on two 8ch cables.
Just use one of the little supplied right angle pin headers that plug into the 8ch io cable and leave the power management board in the box.

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Good to know. When you say the con is I won’t be counting the current do you just mean the current draw from the motor and the servo? If I switch to the smaller power module, is it best to wire it between the 24v battery supply and the power distribution block in terms of the FC monitoring the current draw? I saw that MRO has a new small power module, I’m guessing that is what you are referring to. Also I’ve been reading a lot about placing diodes between FC and the servo or bec, I’m not sure if that matters in this scenario.

So if you use a smaller power module, it will replace the pm07 completely. The pm07 is ok if you have the room, none of them ( power modules) supply a 5v to the servo header. So you still need a bec or an esc or a separate battery for that.

The voltage measure and mAh counter in fc comes from whatever power module is connected to the 6 pin power connector on the fc, and it will only measure what load you have connected to the module, (through the shunt resistor).

Ok that makes it more clear in terms of these specific boards. So its also more obvious now why this board really isn’t great for my application, I could use the smaller power module and connect it between the batter and the power distribution block and that will accomplish what I need much simpler. I can use this to prototype with for testing but I’ll definitely be switching to the smaller module when I can get one shipped. How do most people handle longer runs of the jst 6pin connects? In my case the only thing I can think of is to break out the cable in the power supply box to an amphenol connector up to the control box into the pixhawk or carry it over cat6. Thanks again for the help clearing this up.

No problem, i havent done a large rover yet so a longer cable isn’t something that i have needed yet. You could do any cable type you like, cat6 etc would work, the current and volt signals are both analogue voltage i think (just from memory)

Yeah its not super important at the moment, I’m still waiting on random odds and ends parts to arrive and still working through the electrical schematics for the final install. For now I’m bench testing everything before I move it to the rover frame.

I have a problem similar to yours. How did you solve the 24v servo? have images of how it was to help?

Hi Sean! I am working on a quite similar project as you did. However, I am a bit new to all of this and I was hoping to get in touch with you to see how you did this and ask you some questions. Is there some way I can get in touch with you? Thank you in advance!