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Topic: Controlling Servos (Read 283 times) previous topic - next topic

filaren

Doing a project for school where i use 18 servos for a hexapod. Wondering how i would power these servos. What type of batteries or voltage regulators would i need.

Would appreciate help from anyone that knows anything about making hexpods and what type of power i need

TheMemberFormerlyKnownAsAWOL

Quote
Wondering how i would power these servos
Which servos?

For small hobby RC servos, budget 1A per servo at 6V, as a finger-in-the-air estimate
Please don't PM technical questions - post them on the forum, then everyone benefits/suffers equally

slipstick

With that many servos batteries will need to be Lipos or perhaps Lithium-ion (18650 types). Exactly what servos are you using because the power needed varies a lot depending on the type of servo.

Steve


vinceherman

When I was playing with an 18 servo hexapod, the servos that I had access to ran on 6v.  I used this SBEC and a 3s LiPo battery.
To do it again today, I would use a 2s LiPo directly to modern servos that can run on 2s.
This would greatly reduce problems with power supply.  Simply pick a battery with enough capacity to deliver the needed demand.

Do be mindful of the limitations of the torque of the servos.
It is very easy to exceed the torque capacity of the servos that bear the weight of the hexapod.
In a 3 and 3 gate, where 3 legs are in the air at the same time, only 3 legs bear the weight.  Depending on the length of the legs and the overall weight of the hexapod, the 3 servos bearing the weight might not be sufficient.

In early iterations of my walker, it could easily do a 6 leg pushup from the 'home' position with the belly on the ground, but when it started walking, it could not maintain the stance and sank down low enough that the lifted legs dragged on the ground.  I bought 6 higher torque servos and was able to continue development.

vinceherman

Here is a video of my walker.
http://www.vinceherman.net/robot/media/IMG_0071.MOV
Later I did some smoothing of the gate so it was not as jerky

filaren

#6
Sep 22, 2020, 01:34 pm Last Edit: Sep 22, 2020, 01:35 pm by filaren

With that many servos batteries will need to be Lipos or perhaps Lithium-ion (18650 types). Exactly what servos are you using because the power needed varies a lot depending on the type of servo.

Steve
How would i go about to connect a battery to the servos. Im guessing i would do it thorough a breadboard or something, but how would i go about connecting the battery to it

Idahowalker

How would i go about to connect a battery to the servos. Im guessing i would do it thorough a breadboard or something, but how would i go about connecting the battery to it
Wires. Connectors. Solder.

As a note, I have found that as you add more servos to a breadboard the limits of the breadboard being able to handle the current becomes suspect.Thus, my suggestion of using wires and connectors to connect the battery to the to the servos.

vinceherman

No breadboard.
As Idahowalker states, a breadboard cannot handle the current.

I bought a prototype board.  Soldered on 3 rows of headers. 2 of the rows were ground and power.  I ran a wire along the bottom of the board where the header pins came through and soldered the entire rail to it.  The third was the signal pin.  I soldered on a plug to the power rails for the power to connect (my power was from a SBEC but today's servos can take 2s direct)

Let me see if I can find a pic.

vinceherman



This was the prototype board for my Mega.
You can also use a servo driver like this one from Adafruit or there are less expensive clones on Aliexpress.  They make power distribution easy but I think you give up some resolution on the servo movement.

vinceherman

#10
Sep 22, 2020, 02:34 pm Last Edit: Sep 22, 2020, 02:34 pm by vinceherman


18 servos plugged in to my prototype board.  Note that this was early in the process and I was using a 5A SBEC and a breadboard.  This worked perfectly on the bench.  But in practice, we ran into power problems and upgraded to the 20A. Again, today's servos running directly on 2s LiPo power remove much of the power supply problem.

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