wii nunchuck 4 servo control

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ksj

Well-Known Member
40mm*40mm*20mm
standard servo size
65mm * 47mm * 30mm
large size servo
There are nano, sub-micro, micro, slim-wing, mini, lowprofile, giant form factors as well.
Standard servos typically have 25 or 26 tooth heads.
torque = radius * Force * sine angle
1 ft-lb = 1.356Nm
1 ft-lb = 13.8254954376 kg-cm
1 ft-lb = 191.99999948048 oz-in
1 ft-lb = 12 in-lb
35kg-cm = 2.531554847923463 ft-lbs
60kg-cm = 4.339808310725937 ft-lbs
3304 oz-in = 17.20833337989622 ft-lbs
Basically the weight is going to be somewhere in the ballpark of 460oz in o a 2kg load on the 226cm length of the armature.
but the torque calculation is basically weight times length.
So weight matters a lot. Plus you must factor in inertia with movement. Now the calculation for gravity at earth's surface is 9.8 m/s^2. Now an average gait is 1.4 meters per second and most are capable of 2.5 meters per second.
So lets do some rounding say the gait is 2m/s and the gravity is constant. So if we account for worst case falls and stops you are looking at a multiplier of about 3 for your finished torque calculations for a worse case scenario. But that is so much extra we could probably swing just multiplying the torque calculation on your arm setup by a factor of 4. So 460oz-in need times 4 is 1840. Times 3 it is 1380 and times 2 920. Weight, structure, and servo costs are your main factors here. If you under value things and have a 20% chance of maybe causing an issue it might be worth it but that is a personal decision. Replacing a 40 dollar part every few months is much more budget friendly than buying a 200 dollar part and losing it or having it fail and you have no spares.
So you got your torque calculations, now what?
Now you need to protect the servo horns and hubs from being damaged. This is done either through a gearbox assembly or a servo block. You take the torque and have it rely on the framework of the assembly instead of the servo itself for core strength so all the servo does is movement. Done properly you are not going to have too much frictional drag and even then it is not enough to really be concerned with as that only comes into play in larger higher torque setups like vehicles and large robots.
Bigger shops like Studio ADI and Stan Winston Studios machine their own custom parts. Many individuals either sculpt then cast their pieces or 3d print them. Additive printing techniques for metals is still too expensive to be doable for home every day use so the other option is to go to sites like servocity.com and just buy kits or parts and pieces to build your idea. Just do not expect to buy one set of parts and do not go in expecting to buy all the right parts the first time around.
 

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ksj

Well-Known Member
quick video upload of new setup:
I will be doing some followup videos as I get things setup a little bit better. If there is anything anyone wants covered in more detail, let me know and I will gladly do so. I have no issues imparting knowledge...
 

ksj

Well-Known Member
I just got the second arm (right shoulder arm) built. I am running into some power issues so I will have to recalculate power needs and may have to go with other options. I think the 4700 micro farad capacitor may not be enough for immediate needs.

I am over engineering things so it is far less likely to run into stall situations which will max out draws.
 

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