Cokoino 4DOF Arm

@zander 

Posted by: @zander

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Is this the same kit? https://amz.cx/3Kso

Yep, that's the one.

Posted by: @zander

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What do you think of this kit? https://amz.cx/3Ksp

I think you're gonna send me to the poor house! Now I really want that one.

@robotbuilder 

Posted by: @robotbuilder

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This demo seems to work smoothly?

Except I noticed when it was fully stretched and pointing straight up to the sky.

https://www.amazon.com/live/video/6384286c15494e7192c1926856a77242?ref_=dp_vse_rvc_3

There's something "suspicious" about the first half of this video. To me it appears edited beyond just background music. The arm does not move that fast. What caught my eye was the claw open and close and the hand movements on the joystick. 

However, I would grant that construction quality might be a cause. Joints too tight or loose; poor fittings, etc.

@tfmccarthy Look around Amazon, I found the exact same arms with prices ranging between $35 and $125. I ordered your arm from the US as it was cheaper due to our dollar being up today and recently. Even with shipping it is $30 cheaper. You need to be a bargain hunter. The 6DOF is $35CDN, but no US listing. You can probably order it using amazon.ca for something in the $20 range, check it out or search amazon.com for 6DOF arm.

Posted by: @zander

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The straight up situation is just bad coding, it should be hitting a limit and shutting down.

The orientation of "straight up" is 90 degrees, the half-way point of the range.  (I call this the "hero pose")

The code isn't that sophisticated but, it does implement its own PWM (which I think is almost identical to the "standard" one) and doesn't use the PWM GPIO pins. (That took me a while to comprehend.)

That said, I suspect the jitter in the video is due to the joystick. It could be the servo, but the joystick does fluctuate, and the code accepts that as valid input. That's one of the corrections I made in the code.

Posted by: @zander

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I found the exact same arms with prices ranging between $35 and $125.

I went back and looked this kit up and now recall how I made my selection. I didn't want just the chassis. The chassis you reference does come as a completed kit, but with a matching USA price tag: Robotic Arm Kit $139

I traded one DOF to get the servos, Arduino, and a much smaller footprint. That was a better fit for my plans because the DBWS video already mentions the need to add a DOF for the base (which the one I got already had). The Cokoino arm was Arduino based so my plan to upgrade to ESP32 was clear and I wanted to use the PCA9685.

So, on second thought, I'm gonna pass on the bigger chassis

@tfmccarthy I am not sure what all that means, but when I get the kit I hope it is complete.

Posted by: @zander

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when I get the kit I hope it is complete.

I hope you're right, but the page you reference says:

"Package Contents:
1 * Robot Mechanical Arm Kit(without Servo)"

Nor did I see any reference to the servo type or mention of an MCU. The pictures imply the servos are included, but not the Product Description.

Also, did you note the size of the thing?

@tfmccarthy It's from Amazon so if it doesn't meet my expectations I can send it back for free.

I just cancelled it after reading the reviews and getting a closer look at it. I think I will try to make my own, maybe 3D print using carbon + ????.