Hello everyone it's my first time posting in this forum, and I'm really having trouble on a recent hobby project of mine involving a 6DOF robotic arm kit using mg996r servos. Where on the 'shoulder' and 'elbow' of the arm, the servos struggle to position themselves up when assembled and connected to each other. When ever I try it would struggle to lift the weight, and there's a noise in the gears, but when I carry the weight and help get to the position it can hold that weight in position. At first I thought it might be a power supply issue because I've only used a 5v 2A/3A charging brick, but when I used a rated 5v 40A switching power supply it didn't help. It's my first time using this kind of servo other than basic sg90 on Arduino kits. I hope you can help me give a direction on what I should do to solve this.
Your wire size certainly does not look heavy enough for the currents needed by the servos. Can you measure the voltage AT THE SERVO while moving?
How much weight, connected how, with what lever arm? What is the total torque required of the servo located farthest from the attachment point of the weight?
The absolute maximum torque that genuine MG996R servos can handle is about 10 kgf-cm at 5V, and not for long, or they will overheat.
If you are not sure how to estimate torque, study this tutorial: Pololu - Force and torque
Gear teeth are broken, or gears have slipped off each other (not meshing) and only the sides of the gears are rubbing.
No. You are holding the weight.
Sorry for the late reply. I've set my power supply around 5.3V, and when it's not carrying the weight it remains in that voltage, but when it's carrying the weight there's a slight drop of .1V to .2V, and during the time it struggle or slip/jitter(I don't know if it's the right term) it drops below 4.6V
Hi, @samuxd123890
Welcome to the forum.
This is the spec/data for others to see.
Weight: 55g
Dimension: 40.7×19.7×42.9mm
Stall torque: 9.4kg/cm (4.8v); 11kg/cm (6.0v)
Operating speed: 0.19sec/60degree (4.8v); 0.15sec/60degree (6.0v)
Operating voltage: 4.8~ 6.6v
Gear Type: Metal gear
Temperature range: 0- 55deg
Servo Plug: JR (Fits JR and Futaba)
Dead band width: 1us
Servo wire length: 32cm
Current draw at idle 10mA
No load operating current draw 170mA
Stall current draw 1400mA
We have upgraded our servo gear set and shaft to aluminum 6061-T6.
It is stronger and lighter than copper.
Categories: Servos & Parts, X-Large Servo 50g+
Tom... 
very good
The weight around the 'elbow' part that it would carry is around 450g, and in the 'shoulder' part, it would be around 500g to 550g. In a string close to center it could carry the 500g just fine, but when it's in a lever it would struggle to lift even 60g.
Hi, @samuxd123890
Have you done some torque calculations to see if your servos are being overloaded?
Thanks.. Tom..
Gear teeth are broken, or gears have slipped off each other (not meshing) and only the sides of the gears are rubbing.
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I don't think there are any broken gear because when I opened it they seemed to be intact, but I suspect they are not meshing, but I'm not sure if that's really is it due me not being experience in servos.
Not yet, I'm still studying on how to calculate/measure torque.
If my calculation is correct 'elbow' servo is around 6.82 kgf/cm at 310g and 22cm without the gripper, and with the gripper it's 14.2kgf/cm at 430g and 33cm. With or without the gripper it really struggles, that I'm contemplating whether it's due to it being a plastic gear servo or it's not really a genuine 996r.
You must include the weight of the servos and arm components, and their distances from the point of rotation in the torque calculation.
If it has plastic gears, it is not a genuine MG996R. "MG" stands for metal gears.
Then your PSU is NOT sufficient for the project. With a regulated supply like you have there should be ZERO voltage drop.
Are there no other solution than replacing it with other servo?
You can't beat the laws of physics. If the servo is inadequate for the task, it is inadequate for the task.
You could counter-balance the arms or spring load them.
Elegant - an elastic band.
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