Hi, so I am trying to build a robotic arm that uses servo motors. I understood that I needed to use an external power source to power these motors. However, when I made my schematic, I wasn't really sure if it was going to work. (Only one of the motors is SG90; the other ones are 2 MG996R and 1 MG90S). Thanks for all your help.
Yes, many things will go wrong. Breadboards are for temporary experiments with low power logic circuits, and cannot handle motor or servo currents. The tracks will burn.
The MG996R servos briefly draw 2.5 Amperes every time they start moving. So for two of those, you need a power supply capable of providing at least 5 Amperes at 4.8 to 6V.
The smaller servos draw start/stall current about 1 Ampere each, so 7 Amperes total.
A 4xAA battery pack of alkaline cells can provide only about 2 Amperes at 6V.
Suitable 6V NiMH battery packs can supply many more Amperes and can be bought from RC car suppliers.
Instead of the breadboard, use a servo power distribution PCB, or solder the connections connections from the servo power leads to the servo power supply.
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Sorry, I am kind of new to this stuff. Does that mean that I should get a 6V battery with 7Ah like this one?
NiCad batteries are 3 generations old. You want at least 2 generation old NiMH (nickel metal hydride). Li based batteries have higher current density but are more particular about charging - fortunately there are modules available that can properly feed them.
So it should be fine if I look for a battery that supplies 7 amps and 6V?
Prob lay but see the earlier warnings about the construction of your circuit and the quality of the wiring.
I don't believe you. The metal inside a protoboard is pretty substantial, and the contacts aren't that dissimilar from what's in the JST connectors that normally are used to interconnect servos.
This is a "worst case" number. I'd expect you could get away with a lot less.
Something like this is probably good: Amazon.com
(aside from the fact that I don't particularly trust random-manufacturer batteries, or Amazon 
)
Note that the "2400 mAh" rating means that it should provide 2.4A for an hour, and 7A for perhaps 20 minutes. You don't need a 7000mAh battery to get 7 amps.
Batteries like this (5x 1.2V AA cells) are often used in toy RC things with a couple of servos AND a drive motor of some kind, so I'd think it would work fine.
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You don't have to, because you can try it out and observe the damage for yourself. A number of users have reported the problem, right on this very forum.
Having taught electronics labs, I dealt with breadboard issues on a daily basis and have a rather thorough understanding of their fragility.
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Are solderless breadboards from DigiKey, Mouser, RS any better quality than the cheapies from Amazon, E-Bay, Ali?
Is there a source for higher quality breadboards like those sold by Radio Shack in the 1960s & '70s?
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The last solder-less breadboard I bought was this one (2 years ago):
I am very happy with the quality for pin alignment and grip strength. -
The breadboards from the late 60s, early 70s were great, mine were even gold plated contacts.
TNX, I'll try a few.
- This appears to be the Amazon dot com listing (got mine from Amazon.ca)
- Hint, don’t add the glued double stick backing to the breadboard, it makes things difficult when removing from a mounting plate.
I'm going to name drop from way back: Continental Specialties Corp and their QT Proto Strips. Those things were tough. I think I got about 25 years out of mine before they finally started to go intermittent. And I used (and probably abused) them a lot in that time.
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- I use two (2) breadboards put together on a panel like this:
- I have two such panels so I can easily switch between projects:
- The panel on the left has transparent breadboards.
I find it is difficult to get to the correct hole when viewed from a 45° angle
Breadboards compared:
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@dougp: Thanks much for that Doug, I'm gonna try a couple of the Jamecos.
A hit! 
This I got for like 2 Amps on breadboard. I pluged it out as soon as I noticed something is not good
Use these for the servo power and ground connections.