Hi, I'm planing to power 17 pieces of MG996R Servo for 17DOF Robot Kit.
I want to use 2 pack x 4.8v AA Ni-MH 2600mAh batteries.
All the electronics connected to the battery will be only Arduino Mega 2560 board trough Vin power input and 17 pieces of MG996R.
Servos positive wire will be connected directly to the battery and grounded to the board/battery circuit. Only signal wiring will be connected to the board so the board won't regulate the voltage going to servos.
2 pack battery connect together will give total 9.6v for servos and Arduino board.
MG996R operational voltage is 4.8v to 7.2v
Will this battery fit for power supply my project or the voltage will be a bit to high. I know that there is voltage drop trough Arduino board and servo/waring. Maybe you can advise me based on your experience. Servo wiring is standard factory fitted.
9.6V is too high for the supply to the servos but will be OK for the Arduino. It would, however, be better to use a buck converter to reduce the 9.6V to 5V and feed both the servos and Arduino with 5V
This batteries I want to buy are specs like below: Capacity: 2600mAh Measured at 520mA (0.2C) discharge. Max Discharge Current: 7,800mA Max Charge Current: 1300mA Internal Resistance: <25mOhms per cell at 1000Hz battery fully charged 4.8V 2600mAh AA - Flat Dimensions (L x D x H): 57.6 x 14.7 x 50.8mm Weight: 112g
It's mostly about the size and weight. This batteries 2 pack will fit on the foot of the robot stabilizating the legs and not disturbing servo moves and they are not heavy too but the Amps they can provide and for how long can power 17 servos if they can at all.
Any batteries you recommend in line with voltage regulator to power 17 DOF robot for like 30 mins preprogrammed sequence of moves. It's a budget project.
Or maybe powering each 2 pair of servo separate locating batteries around the body not only legs wil be good idea.
The bracket kit is one of those popular on eBay
If you'll notice, the battery capacity is listed at a discharge rate of 0.2C. Here, C stands for the battery capacity. In this example, a discharge rate of 2.6 A would be at 1C.
NiMH cells just don't give the high discharge rates of Li-ion or Lipo cells. A pack with 2 Lipo cells would give a nominal voltage of 7.4V, but could be as high as 8.4V when fully charged. It may still damage your servos. And the higher the voltage, the greater the current draw.
And looking at the structure, it is likely that most of the servos will be active at the same time.
Whatever batteries that you choose, all the battery grounds need to be connected to the Arduino ground as well as grounds of the servos that the battery is powering.
A pack with 2 Lipo cells would give a nominal voltage of 7.4V, but could be as high as 8.4V when fully charged.
I have 7.2v 3300mAh NiMh Battery powering 6 servos they did not get damage yet but making ''buzzing'' sound. I think higher voltage might be the issue.
I think I'll go for 2 x LiPo batteries, there are some 2200mAh 3S 11.1v 35C Li-Po on sale. Might be to big but I won't safe much buying something less that this. Some voltage regulator and this batteries should provide power for half an hour of fun for this MG966R servo. Per specs is always different if compare to real life measurements.
I am concerned that you will fry the servos at this voltage. You mentioned going though a voltage regulator. You will need to check how much current it can supply before overheating. You will need to draw a lot of current.
But your problem with the supply current will still remain. You will need to check the 'C' rating of the pack, and whether you can actually trust it. They are usually over-optimistic, to put it mildly.
Specs of 2 pack LIPO 2200mAh 3S 11.1v 35C that I'll buy:
Length mm 100
Width mm 34
Depth mm 22
Weight (g) 168.8000
Voltage 11.1
Cell Number 3
Battery Capacity 2200
Discharge Rate 35C Constant
Chemistry LiPo
Burst Discharge 50C (8 seconds)
Lead & Balance plug Silicone leads, JST-XH balance wire & plug
Charge Rate 2C Max
Power Pack Cells and Voltage 3S – 11.1v
Watt Hours (Wh) 24.5
There are on sale in UK for 17.50 GBP. I think I won't buy any better per specs. over the internet.
I think I won't spend more on this, it's not like drone or something, I can always charge them unlikely can not charge drone during flight.
Any voltage regulator to recommend? I was planning to use AITRIP Adjustable LM2596 LM2596S regulator. Maybe something more reliable with set voltage or regulated?
I've checked the regulators and it doesn't look optimistic per specs and budget.
So per specs there is a choice between 2 pack LIPO or 2 pack NIMH batteries and with current of 20 to 25 amps each total 40 amps to go low on budget without regulator but there is a risk of high voltage 8.4V when fully charged so there is still need for regulator.
Minimum by specs regulator and one of the cheapest on the market I can use is 20A 300W DC-DC Buck Converter
Per spec it can adopt 75V / 80A and give 20A (15A for sure) so this does is only 30amps from 2 pack batteries and 2x regulators.
Did someone actually damage servo with 7.2v lipo battery? The easiest way will be to power 17 servos with 2 pack of 2S 850mAh 30C Li-Po batters this will give 850maH x 30C = 25.5 amps per battery so 2 pack of 2S 850mAh 30C Li-Po will be 50 amp and 1700 mAh
Specs of the batteries:
|Balance Connector|JST XH|
|Watt Hours|5.9Wh|
|Weight|60g|
|Capacity|850mAh|
|Connector|No Connector|
|Max Continuous Discharge|30C|
|Voltage|7.4V (2S)|
|Dimensions|56 x 32 x 17.5mm|
I don't know how much I can trust this specs as it says ''Max Continuous Discharge|30C|'' it can be for 5 min and then 10C and I'll end up with 10amps instead of 25amps out current
There are some budget HiMH 7.2v packs batteries but I don't know the current like this 3300MAH 7.2V TORNADO. Maybe this will be better to use without regulator. Anyone knows how much current HiMH 7.2v packs 3300MAH can give?
And there is still the voltage drop trough the whole system but I don't know how much it will be. It's only wiring/connectors and servo so I'm guessing it won't be much.
Looks like you have done a good analysis of your situation.
I don't know if the servo is rated for a 2S Lipo pack. If it does say so, then you should be good to go with 2S lipos.
You also won't need a voltage regulator for the Mega, if you feed it through the power in port and not Vin.
I've made mistake writing the last post. I was thinking 2s lipo pack in total but connected together 2x 2s Lipo will be to much voltage.
Finally I ordered 2 x 2200mAh 2S 7.4v 35C Li-Po Battery. I'll power one side with one battery and another side with second battery. There is a lot of wiring and connectors in the system as well as the Arduino board to power for voltage and amp drop trough it. My servo should handle it, this are big MG996R 7.2v servos Lipo when fully charge will give 8.4v, hope it won't damage servos. Will see. Everything takes time. Will give updates about this powering solution.
