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Servo choice
#11
On the original model, the servo screw holes are just right for M4 bolts. The chassis holes take M3 nuts and bolts just fine.
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#12
Shortsighted is my middle name. Wink

I've been meaning to go back and make the design more like the original and fix a couple problems I've found, captive nuts being one of them, but haven't quite gotten to it yet. I'll work on it tonight. 

I also have to modify the top plate, bottom plate, and shoulders, add labels to the parts so when they print off it's easier to identify which limb is which, and add recommended printing orientations. Any other issues with the models you've identified?
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#13
Don't get me wrong, they aren't issues persei Big Grin I don't want to sound ungrateful to those who've laid the framework of this great project.

I started messing about in Fusion 360 to modify some of the parts to solve annoyances or to improve on bits, but unfortunately we don't have access to original cad files for KDY's bits afaik, only the steps you've provided for your modified bits.

I'm not great in F360, still learning but have years of experience in less "accurate" tools like blender and am a software engineer by day, so have a desire for doing things right Smile

One thing a colleague who I introduced to this expressed was his confusion about what bits he needed to print etc, so one thing that would be good is if we can somehow improve how the various versions of parts of stored / linked and referenced. What I mean by this is what bits are common between servo types and which bits aren't, I worked it all out after a little reading and looking around but for a new-comer like him I agree it could be a bit confusing / daunting.
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#14
You power your plastic servos at 12V? You are a brave man. Let us know if the case melts first, or the electronics fry, or the motor brushes light up as their last action ;-D
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#15
(08-26-2019, 09:27 PM)MattthiasM Wrote: You power your plastic servos at 12V? You are a brave man. Let us know if the case melts first, or the electronics fry, or the motor brushes light up as their last action ;-D

Turns out the PCA9685 was the first thing to go. There's a small enable transistor that very much did not like getting 12V 5A pulled through it and let out the smoke very dramatically. The limit on my power supply is current so I think I'll switch to a 2S LiPo, perhaps with a regulator. I'm not sure that the PCA9685 will be able to distribute the 60W or so required by the servos at max power without burning up, and am unsure how else to go about power distribution without soldering a custom solution (oh please no!). It seems like that power transistor may depend on the variant of the board that you get as I have a spare that doesn't appear to have the enable transistor at all. That being said, I'm not sure the teeny board, even without the transistor, will survive 60W.

I'll be sure to let you know what the second thing to melt is. Wink
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#16
I'm looking at a servo from Bangood that is rated at 20kg-cm at 6v. It's this one:
https://www.banggood.com/Towerpro-MG958-...ds=myorder

They are $11.55 USD each. With an adequate power supply they should be enough for the robot.
I hope to have time tomorrow to do some torque test and compare them with the 996.

Dave
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#17
I test printed the Midarm to see how it would fit with the MG958 as in CAD it looked like the arm would be just a bit too small to fit. Fits perfectly.

I need to mod the files though as the nut slots are too small for M3.

   

Dave

The servo horn slot needed some massaging as well. I have managed to extract separate step files so I can make the changes. I'll post an update when the next midlimb is printed

Dave
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#18
i use cls and they work very well!
Electronic engineering student, Maker, 3D print guru, grew up with Arduino and Raspberry, FPV drone racer.
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