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****Motors Selections - Listed Smallest to Biggest****
Micro N20 ------- Brushed DC Motor ------- 1-3.7v ------- $1 ------- uses: eyelids, maybe facial expressions?, eye movements maybe?
Brushed DC Motor size 140 ------- 5v ------- $0.86 ------- uses: eyelids, maybe facial expressions?, eye movements maybe?
Brushless DC Motor size 2430 ------- 5800kv ------- 24a ------- 7.4v ------- 200 watts ------- $15 ------- uses: finger joints, most small muscles overall - most used in robot like 150+ of them
Brushless DC Motor 1/16th 1/18 RC size 2838? ------- 12.6v -------24a ------- 300 watts ------- $27 ------- uses: maybe larger arm muscles like forearms or wrists? also back, abs, neck, etc misc muscles maybe
Brushless DC Motor size 3650 1/10 RC ------- 13v ------- 69a ------- 900 watts ------- $28 ------- uses: maybe larger arm and torso and back muscles or forearms or wrists
Brushless DC Motor size 4082 1/7 RC ------- 36-52v ------- 64a ------- 3400 watts ------- 930kv ------- $65 ------- 1.4Nm nominal 4.35Nm stall uses: beefier thigh and leg motors etc
****Downgearing 2430 BLDC Motor for Fingers****
****21:1 downgearing for fingers layout:****
2.7:1 downgearing on turn in place pulley mounted to motor at first;
next, archimedes pulley downgearing 8:1 in total using a double pulley with a top pulley paired with that to
get 4:1 and then another pulley to get the 8:1 just below that first double pulley; so that 8:1
combined with the 2.7:1 earlier gives 21:1 total downgear ratio
********string runout relevant to downgearing 21:1 ratio:*******
32" starting draw onto motor shaft
32"/ 2.77 = 11.55" total draw after that first pully mounted to motor
11.55" draw / 8 (archimedes 8:1 downgear) leaves 1.44" final output at joint and about 2/3 of this is just removing slack in tube pathing and archimedes system
and string connections to bones etc etc way more slack that I ever anticipated originally and this 1.44" is necessary as total final draw
note: if we want higher downgear ratio, say 42:1 then we'd need to double the initial draw to 64" and then have the 64"/2.77 = 23.1" at the first archimedes
pulley and so to cut down that huge remaining runout would surely need a second turn in place pulley maybe 2:1 so 12" total runout that we send over to
the archimedes 8:1 downgear which will bring it to ~44:1 total downgear since 2.77x2x8 = 44 --- and I do think 44:1 is ideal but just felt cramped for
space and not up for redoing things at this time for first joint maybe; open to try this later and maybe place the turn in place pulleys somewhere else
like at the tip of one of the bigger motors or something not sure...
note: my actual hard numbers for runout on first motor for index finger were 34.57" draw then 12.48" draw after the turn in place pulley then 2.52"
draw after the 4:1 double archimedes pulley then 1.26" draw after the last archimedes 2:1 downgear pulley; this 1.26" sounds like overkill but actually
all of this was needed due to slack everywhere that has to be pulled taught before finger moves - slack in tubing, slack in archimedes system itself,
slack in string attachment to stretchy spandex bone sleeves, etc
2430 motor at 1/2lb pull initially is then 21*0.5lb or 10.5lb pull after downgearing which might be more like 5lb after factoring in mechanical disadvantage at joint
****Calculations for the Elbow Joint****
A reliable reddit user told me 40Nm is minimum for a decent human level elbow joint and 60Nm is preferred.
I replied:
For the brachialis (elbow), I plan to use a 3660 bldc motor for and it is 1Nm normal torque and 3Nm stall torque
but after 32:1 downgearing it's 32Nm normal torque and 96Nm stall torque. Next, for the biceps brachii
(also for elbow) I chose the 4082 bldc motor which is 1.45Nm normal torque 4.35 stall torque but after
32:1 downgearing it's 46Nm normal torque and 139Nm stall torque.
So the combined of the two elbow muscles is 78Nm normal torque and 235Nm stall torque. You said 60Nm is the
minimum so we are about 25% above that as a nice margin. We can actually double our torque as wel if we go
64:1 downgearing if needed or add another motor if needed.
Note: I think it's pretty cool my stall torque is 4x the 60Nm you mentioned. As long as we are below stall
torque, the motor will still move the load just under max strain and will heat quickly etc but can move it.
So it seems I am very much solid on my motor selections in this joint example.
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