Cell B3, Motor Seperaation.
The spreadsheet note says it masured betweent the chain attachment points but
I’m not clear where these are. Is this dimension measured between the center
of the motor drive shafts? Distance between sprocket teeth at the twelve
oclock position? I just want to make sure that I use the dimension properly.
center of motor drive shafts (which is also the same as sprocket teel at the 12
o’clock position)
for the purpose of seeing the force available, a small amount of error isn’t
going to matter much
Location References
Am I correct in interpreting these to mean the location of the center of the
router bit is above the referenced location? For example, top right means the
center of the router bit is over the top right corner of the work area.
That is an assumption that may not always be correct. 30Kg cm is the rated torque of the entire motor/gearbox unit as far as I know. It is not safe to assume that the motor will stall at that rating. Stall torque is a different rating. 30Kg cm is likely the ‘do not exceed’ design guideline torque. Meaning it is the user’s responsibility to monitor and not exceed that torque.
The electrical part of the motor is rated 12v @ 1.5A 18 Watts electrical input power. Obviously we exceed that in a stall, based on burnt 2A drivers.
30kg cm torque @ 20rpm equals only about 6.2 Watts mechanical output power.
So, either these motor/gearbox combos have remarkably bad 34% efficiency which I don’t believe, or the 30kg cm rating was issued because the weak link is the gearbox, as we have learned.
The power lost between input and output has to be absorbed somewhere. It went toward eating gear teeth.
I’m going to just wild guess 70% actual efficiency for the combo. Assuming the same 20rpm, thats 12.6 mechanical output watts at MOTOR rated input. That could result in 61kg cm output torque. 2 motors pulling against each other could be 118kg of force on the chain. torque in kg cm/1.02743 = force in kg
NOTE this is all theoretical without any actual measurements made. I would be interested to hear the results of @Gero spring scale test to see how far off my guess was.
Hopefully I haven’t done any circular calculations here, but it looks like we aren’t exceeding motor design limits, but we are exceeding the gearbox design limits sometimes.
Also, we are talking about 18W gearmotors here and completely neglecting the effects of a 1500W router tearing through tree carcasses. The load CAN exceed the 30kg cm rating.