The documentation states the AL5D can lift approx. 13oz at the end effector. In a worse-case static torque calculation, I estimated a number to be greater than what the HS-805BB can support.
Assuming the arm to be straight (sin(90)), and assuming point masses at each joint, (and even ending at the wrist - not including end effector which would increase torque), I calculated there to be roughly 270 oz-in needed at the shoulder joint. This would allow for a max static load of 5.56oz.
Concluding that the 13oz lift capacity was acquired through experimentation and not calculation, it leads to ask how can one predict what sized servo you need to overcome some load. I would have assumed to lift 13oz you would need a gear box at the shoulder joint.
Theory is always different than practice. Take a look at the Robot Arm Torque Calculator: robotshop.com/robot-arm.html
The 805BB can theoretically support 343oz-in.
There are two ways to design a robotic arm:
Based on the desired load to be supported
“You get what you get”.
Most robotic arms take the second approach - use servos which make sense at each joint, don’t overdesign, and then see what load it can support. We (Lynxmotion) have the ability to change the servos at each joint easily, as well as the length of each section, to find the best combination. Note that the brackets are made for specific servos, so there are not a ton of choices.
For example, the M100RAK was designed using power gearboxes, but the exact load it would be able to support was not known until the prototype was built. This approach was taken mainly because there were not a lot of choices for parts when the arm was being designed. The lengths of each section was chosen to mimic the arm of an adult human.
If you want to take the first approach, you need to calculate the torque required at each joint, and ideally multiply this by a safety factor (25%… 50%?). Your arm should then be able to lift what you designed it to lift and ideally a bit more.
