Robot arm wiring diagram questions from a beginner

Projects General Guidance
1

Beginner here to both robotics and electronics, I have created a circuit diagram with help from a youtube video (but with a few changes). The aim of the circuit is to power 3x MG996R servos in a robot arm. However I have a few questions regarding it:

  1. Is my wiring correct? what changes should I make?
  2. Is the gauge of wire I've put appropriate?
  3. How and where would I add an electrolytic capacitor to smoothen out the movement of the servos? and how do I calculate what rating is appropriate?

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The arduino is powered by USB to a computer which also powers the PCA9685 via the VCC pin, no servo power is routed through the PCA9685 nor the arduino. The original video showed servo grounds going to the PCA9685 then to the ground terminal bus, but I've routed servo grounds directly to the bus.

I guess a final question is, does anyone have a better idea for the power supply? I've found it difficult to find a power supply which is 6V and provides decent amperes (at least here in the UK). The voltage and amperes here is based off of a bench power supply that can only provide max 10 amperes, 30V. Theoretically the amperes provided would be okay, but if I add another servo or even two servos it would not be enough to meet the stall current requirements.

Apologies if I take some time to understand things!

2

i dont understand the bus part but why dont you use thge pca and an external power to use the servos? i have use some micro servos with the pca with no problem, you can smothen the servos movement by a delay in each step eg delay(35)

3

you could use 4x AA bateries thats what i did

4

If your power has to come from a battery as opposed to a mains-powered supply, then, going to extremes, I would recommend a golf cart battery. 6VDC and a LOT of current. If the form factor is too much, then VAPE batteries are possible, BUT it is critical to your survival that you have a proper charger and protective discharge circuits. I seldom recommend 18650's in parallel due to the extreme danger, but it can be done (I slept on hundreds of them) if you have the correct parts for a BMS. The oft-quoted TP4056 is VERY incomplete.

5

are vape batteries rechargable?

6

also, you could use a battery of a freestyle fpv drone but you should be cautious when charging it

7

"Are rechargeable" is not the same as "can be accessed to charge"

The battery is usually an 18650, standard for rechargeable.

If you buy the "cheap, US$25" single use, no access to charge, but still rechargable at your own risk. The UD$300 models refill and recharge.

8

so with 25 dolars you get a vape with a battery accessed to charge

9

Really? They seem to be dosed to be disposable at that price.

10

They are, but the fact you asked tells me you are NOT battery literate, so your risk of explosion and fire is VERY HIGH unless you get educated.
The most faked item on the net is 18650 batteries.
The max capacity of a 18650 Lithium is between 2,000 and 3,000 mAh any more is a fake.
The reason I said VAPE is that they have the ability to produce higher peak amps.
A proper charger like the RC Sky MC3000 is needed.
You will need a proper BMS if the batteries are to be wired in parallel (not likely with Vape batteries), but I would use one in any case.
Get proper advice, not videos, start at Battery University. Good luck.

11

The MG996R briefly draws the stall current (about 2.5 Amperes) every time it starts moving, so for three of them you need a power supply capable of delivering about 8 or more Amperes, at a voltage between 4.8 and 7.2V.

Look for a power brick with those specs.

1 Like
12

What do you mean by 'accessed'?

13

Please explain 'dosed' and the meaning of your post.
Is English your second language?

14

Please explain 'no access to charge' and UD$300? I have bought plenty at prices less than 1/50 of that.

15

Thanks for the reply. These MG996Rs are a little bigger than 9g servos and have quite a high stall current each (2.5A) so I'm feeding a higher current (10A) into the circuit to support them. The PCA9685 only supports 10A. So to be safe and prevent overheating/damage, I was planning on powering them externally so no servo power goes through the PCA9685 board nor the Arduino. The only connection the servos have to the PCA9685 is the PWM leads pins. This is also somewhat future proofing it so I can add more servos later if needed.

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16

You can get the same battery the Swiss Guy recommends from AliExpress for 10 for $41.66 or 1 for $6.70 and 4 for $18.30. These are free shipping. Look for the following. I did not provide a link as they change often. LiitoKala is the brand.

1-12pcs LiitoKala Lii-35A 18650 3500mAh 3.7V Li-Ion Rechargeable Battery 10A Lithium Battery High Drain For Flashinglight Vaping

17

For 10Amps? That's 10,000 mA, how much capacity do the batteries have?

18

Thanks for the reply. I feel I should have been clearer in my post, I was originally planning on using a bench supply that can provide (max) 30V 10A which would be perfect for this application (3x MG996rs). However if I decide to add more servos later on, this bench supply would no longer support the ampere requirement, so I was looking into higher ampere power supplies that can provide at least 6v-7.2v (for maximum torque). So maybe 6v-7.2v 20A.

19

Thanks for the reply, those batteries look good. Presumably if I wire two of these in series I would get 7.4V 10A, then wire 2 more in parallel for 7.4V 20A, so 2x2?

My servos support a max voltage of 7.2v, so presumably I'd need to step down this voltage?

I actually have a hexapod kit that uses this kind of battery setup, so I already have the chargers.

20

Correct. For reliable operation, the power supply must be able to supply at the very minimum 2.5A x (number of servos). I would add a safety margin of a couple of Amperes.

You would be taking a chance with a 2S LiPo battery pack, because the voltage (8.4V peak) exceeds the MG996R specs. There are other heavy duty servos that are designed to operate safely from 2S LiPo packs.