Hardware Setup for Servo Control

Discussion related to "under the hood" OpenMV topics.
gabriel_colon32
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Hardware Setup for Servo Control

Postby gabriel_colon32 » Mon Dec 21, 2020 8:10 pm

Hi! I've looked a bit on the examples and docs about servo control, but I still cannot move my servo. I believe it has to do with my doubt about the power supply for the servo itself. Do I need an external power source for the battery or could I use the VIN and GND ports?

I also believe it might a hardware issue with the pins not connecting properly. Is there a way for me to check if they are passing current?
Thanks for your time!

-Gabriel
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kwagyeman
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Re: Hardware Setup for Servo Control

Postby kwagyeman » Mon Dec 21, 2020 8:36 pm

You have to provide an external power source for the servo. VIN powers the camera. It’s not a power output.
Nyamekye,
gabriel_colon32
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Re: Hardware Setup for Servo Control

Postby gabriel_colon32 » Tue Dec 22, 2020 11:13 pm

So there are no power outputs on the board?
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kwagyeman
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Re: Hardware Setup for Servo Control

Postby kwagyeman » Wed Dec 23, 2020 11:57 am

Yes, you can get 3.3v from the 3.3v pin.

To be clear... you should NOT power a servo from your computer's 5V USB.
Nyamekye,
gabriel_colon32
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Re: Hardware Setup for Servo Control

Postby gabriel_colon32 » Wed Dec 23, 2020 4:35 pm

So I can't power my camera from my computer and use the pin? And the negative cable I just put it on GND?
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kwagyeman
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Re: Hardware Setup for Servo Control

Postby kwagyeman » Thu Dec 24, 2020 12:56 pm

You should attach a secondary voltage source for the servo not from the PC. Like a battery. Servos draw a lot of current and will cause issues on the USB bus.
Nyamekye,
NoBearSnack
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Re: Hardware Setup for Servo Control

Postby NoBearSnack » Thu Dec 24, 2020 1:29 pm

Is a relay board a good way to allow the pin from the OpenMV H7 to turn power "on" to a servo while it takes power from an external power source (like a battery)? Or is there something more simple that will do the same thing, like a relay switch, so that a relay board isn't needed?

Will the pan and tilt shield allow plugging a 12V car battery into the servo shield to power the H7 plus AND three servos, or do those servos still have to be connected to external power?

Can the servo shield be used with the wifi shield and still power three servos? Some stuff I've seen online suggest that can't be done.
NoBearSnack
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Re: Hardware Setup for Servo Control

Postby NoBearSnack » Mon Dec 28, 2020 1:19 am

I bought the pan and tilt shield and when it comes in I'm hoping I can power the H7 from a 12 volt battery and use the shield to power three servos. My understanding is that's what the shield is for, taking input power and using it to power servos.
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kwagyeman
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Re: Hardware Setup for Servo Control

Postby kwagyeman » Mon Dec 28, 2020 2:18 pm

Yes, this shield can do that. However, keep in mind you're dropping 12V to 5V with a large current draw. This is going to produce a lot of wasted power heat on the voltage regulator. It would be wise to give the shield no more than 7.4V or so from a standard 2S LIPO battery.
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NoBearSnack
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Re: Hardware Setup for Servo Control

Postby NoBearSnack » Tue Dec 29, 2020 3:01 pm

I guess I should have said H7 Plus. I saw a recent post from you about it not having a servo 3 but I don't know if that applies to the pan and tilt shield. I can get by with only two servos though.

Will the pan and tilt shield work with the WiFi shield? I think I read somewhere that those two shields used the same pins and couldn't work together.

Good information about the input voltage, thank you. I will have the H7 attached to a Relion 12 volt, 20 amp, lithium battery. If I need to step the voltage down from 12 volts I may need to buy a regulator to regulate the power before it gets to the Pan and Tilt shield I suppose. The servos will rarely be used and activation should be brief.
NunyaBinnez
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Re: Hardware Setup for Servo Control

Postby NunyaBinnez » Thu Jan 07, 2021 2:32 pm

NoBearSnack wrote:
Tue Dec 29, 2020 3:01 pm
Will the pan and tilt shield work with the WiFi shield?
I would also like to know.
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kwagyeman
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Re: Hardware Setup for Servo Control

Postby kwagyeman » Thu Jan 07, 2021 4:48 pm

The WiFi shield uses too many pins. So, they won't work with each other. You can use the servo shield however.
Nyamekye,
NoBearSnack
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Re: Hardware Setup for Servo Control

Postby NoBearSnack » Fri Jan 08, 2021 3:10 pm

Thanks for the follow up, I'll get a servo shield and use that with my wifi shield instead.

Since the servo shield doesn't regulate input power like the pan & tilt shield, I will do some research on how to power the H7 and the servos from my 12.8V 20 amp battery.

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