Newton's second law F = m*a, will give you the force required to move a mass. Disregard friction and use the BOE BOT servo specs to come up with a ballpark value. More information can be found in a college 101 Physics text or poking around online.
Just because it CAN move something doesn't mean it will last in that application. Servos are designed more for accuracy than max load potential. They have small motor and tiny gears, more load will accelerate wear. I would say use good sense and keep the loads light if you want it to last a while.
Newton's second law F = m*a, will give you the force required to move a mass. Disregard friction and use the BOE BOT servo specs to come up with a ballpark value. More information can be found in a college 101 Physics text or poking around online.
Thanks Mike, I found the specs at the Parallax web page here which gives 43.1 oz-in torque at 6 V. This is approximately 2.7 lbs.-inch. I know from F=MA that you don't want to accelerate Boe-Bot too fast or the force will increase. So slow starts and slow stops are necessary for carrying a larger mass. I was not looking for theoretical but rather actual experience of adding weight to a Boe-Bot. Given good tire gripping on a stable even surface, how much weight can Boe-Bot move? With a home weight scale, the mass to be moved is determined to be about 1kg which is about 2.2 pounds. It looks like I will need to try it and see how it works.
Just because it CAN move something doesn't mean it will last in that application. Servos are designed more for accuracy than max load potential. They have small motor and tiny gears, more load will accelerate wear. I would say use good sense and keep the loads light if you want it to last a while.
Erco, good points. My idea is to use slower ramping startups and stops to minimize acceleration and reduce stress forces on the servos, realizing these gears are plastic and tiny with motor parts that can wear. After I get full use out of moving a 2.2-lb mass around for project demonstrability, the servos could be replaced for the next project.
Not all servos are created equal (a risky thing to say on MLK day). Some have metal gears, some have ball bearings on the output shaft, some have both. These increase the ultimate load capacity, but supposedly the metal gears wear quickly anyway. Nylon/delrin gears are inherently self-lubricating and last much longer at their lower design loads.
The servos will be stock servos found in the Boe-Bot carry project. Although other servos are possible replacements, the project will use all Parallax stock components (or it would not exactly be a stock robot).
Since the load weight now falls well within one servo spec, and there are two servos, the weight should be carried well with no problems or undue wear and tear.
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