Sir,i am building gesture controlled robotic arm in mobile platform.I am using dc motors for mobile platform and 7 servomotors for arm which has two links and one gripper.
I am using 4 12v dc motors,each needs 2amps and 4 16kg-cm servomotors,each needs 2amps and operating voltage 7.2v@16kg-cm and 3 35kg-cm servomotors,each needs 3.5amps and operating voltage8.4v.
Now,i have selected to use one 12v 7.2ah battery for 4 dc motors and one 9v,3.7ah li-po battery for the 7 servomotors(because it has 5c current rating as you said).
my bot weight is 8kg.Now,i want to know,is that power source is ok for my requirements?
link for 35kg-cm servo: robokits.co.in/motors/rc-servo-m … ervo-motor
To confirm:
4x 12V DC motors (2A each)
4x 7.2V RC servo motors (2A each)
3x 8.4V RC servo motors (3.5A each)
Your 12V battery cannot be used with either servo motor, and a 9V battery might burn the servo motors as well. Note that the servo you link to operates at up to 8.4V, so there’s no guarantee that it will work at 9V (might burn).
Given the range of voltages, you might see if the servos have an overlapping voltage range, and either choose two batteries or a 12V battery and a powerful voltage regulator.
A 9V battery does not seem suitable for any of these actuators.
Sir,you are saying that i cannot use 9v battery to power 8.4v servo,but you are saying that try to choose either two batteries or a"12v" battery to power the whole system.I can’t quite get it? or am i wrong?
Not quite.
To power the 4x 12V DC drive motors, you should use either a 12V NiMh or lead acid battery pack or an 11.1V LiPo pack (we can determine capacity and discharge rate later).
To power the 8.4V servos, you will need to either use a separate battery pack, or use a high current voltage regulator; you would split the 12V pack: one part would feed a voltage regulator which would power the servos, the other would remain 12V.
To power the 7.2V servos, you would either need a third battery, find a common operating voltage with the servos above, or use a third voltage regulator.
We do not suggest powering an 8.4V servo at 9V is 8.4V is indicated as the upper limit of the input voltage.
Thank you for your clarification sir.
if i chose to power the 8.4v servos with separate battery pack,would i get the battery with the 8.4v? and same question for the 7.2v servos.
If you opt for a multi-battery setup, you would try to choose a battery pack which matches (as closely as possible) the nominal voltage of each actuator.
For 7.2V, you might consider an NiMh pack (1.2V per cell x 6 cells = 7.2V) or a 7.4V LiPo.
For 8.4V, that would be a 7 cell NiMh pack.
Normally these should have a voltage input range, so check the specs.
The one servo you linked to can operated at 6V to 8.4V. What is the input range for the other servo?
For other servo the voltage range is 4.8-7.2volts.
Suppose,if i use these battery pack,will it satisfy my current reqiurements?
Servo 1: 4.8V to 7.2V
Servo 2: 6V to 8.4V
Therefore the overlap is 6 to 7.2V, so you can choose a 6V or 7.2V battery pack. Don’t use a 7.4V pack.
This way you would need one 12V pack for the drive motors, and a 6V pack for the servos.
Sir,Thank you for your suggestion.
if i use 7.2v battery pack ,wiil i be able to get the highest performance of 8.4 volt servo?
If i use one battery pack will it satisfy my current requirements?
total current requirement for servos:
For 4 16kg-cm servos each needs 2amps,totally 8amps.
For 3 35kg-cm servos each needs 3.5amps,totally 10.5amps
therefore total current requirement is 18.5amps.
A 7.2V pack should work with both servos. In terms of optimal performance, it’s within the range, so it should be fine.
If you plan to operate all servos at max torque all at the same time, the battery pack would need to provide 4x2A + 3x3.5A = 10.5A = 18.5A continuous current (worst case scenario).
You would need a battery pack which can discharge at that current, and then figure out what capacity you want.
I want it to provide power for one hour.how can i select the battery for these reqiurements?
7.2v,?AH.
If you plan to operate all servos at maximum torque for the entire hour, you’ll need a 7.2V, 18.5Ah battery pack (or somewhere between 18 and 20Ah).
However, note that RC servos have a duty cycle of only around 25%, and operating them at max torque for a full hour can damage the servos.
Sir,i could not find the battery with 18.5Ah.could you tell me how much Ah battery should i buy if i reduce the time to half an hour?
Is the discharge rate for all NImh battery 1.5c or it may varies?
You would need more AA batteries than is worth it. We sell a 6V, 10Ah battery pack here:
robotshop.com/en/6v-10000mah … =RB-Sta-11
You could start with one and see how much operating time you get.
