Servos not working with 9V battery, works with USB

Other Hardware Motors, Mechanics, Power and CNC
1

So I am trying to make two servos work as wheels, and it works perfectly fine when plugged into a computer. However, when I plug it into a 9 v battery they just make a weird jerky movement? Almost like they start to spin and then stop

2

Servos require significant current, which your 9V battery won't provide. Particularly when starting, the servo may draw several hundred milliamps, depending on type, design, etc. etc.

3

So I need a bigger battery? How much would you recommend?

4

That will depend on the stall current of your servos.

5

To start with, four AA in a holder, or better yet four C or D, if you have access to those.
Nothing more than 6V, either.

6

I tried the 4 AA previously and encountered the same issue so I switched to the 9V.

7

Now I want to know details about your servos, because there's a wide variety. These aren't TowerPro SG90 hobby types, then, I take it?
Provide a link on the web, if you bought them.

8

I wasn't the one who bought them- I was given them for a project by a teacher. Anyway- they are two different kinds the first says futaba s3004, the second says hitec hs-485HB

9

Couldn't find current spec for the futaba, but the hitech
|No Load Operating Current Draw|200 mA|
|Stall Current Draw|1,200 mA|

So definitely a significant current load for batteries.
Can you operate only one?

10

Actually update, I found out there was a short in the breadboard and switched to another one and it works now with the 4AA

11

Wrong way - AA's provide more current (though many AA battery holders are not good for high current). Servos and motors take lots of current, its common for newcomers to severely underestimate their requirements. The smallest servos can use 1A peak or more, larger ones are much higher.

LiPo, SLA, LiFePO4, NiMH are possible battery chemistries for high currents, and avoid cheap battery brands if you can. Watch out for those rivetted AA and AAA battery holders, they often have significant resistance as the parts are not welded together.

12

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