XL_Quad

[Xevel]

I started, to demo the USB2AX Pro and various Dxld Dynamixel devices, a little quad robot umade with XL-320.



Full Album : https://goo.gl/photos/okZSp7jzWNRkBvD88

[r3n33]

Cute! I like it.. lots of parts hey?

[tician]

Quad with 3-DOF per leg and no servos contributing to the moving mass of the leg and lots of symmetry. Quite nice, but can it turn very well? Forward/backward and strafing should be very easy, but turning seems like it might require lots of bobbing about.
edit: or not. Now that I think about it, turning should be quite smooth.

[Xevel]

You might have a look at Spot Mini for ideas about motion, though it won't be as cool...
It still misses a few parts, for the head, the lidar and dynamixel devices to read the potentiometers.

[jwatte]

That is frickin' beautiful!

Why did you try potentiometers on the legs, though?

[tician]

Why did you try potentiometers on the legs, though?

Torsional load sensors, maybe? Difference between internal pots and external pots would give rotational displacement of shock material which would give torque if the material properties are well characterized.

[Xevel]

Yep, as Tician said the potentiometer ends up serving as a torque sensor among other things.
The torsional element is a custom piano wire spring, that is described well enough by Hook's law.

It measures the deflection of the arm from the output of the servo, so I can use it directly to compute torque, and also add its position to the servo position to get the absolute rotation between the servo and the leg. I then plug that into FK equations (simple enough in this case) to get the foot actual position, and mix that with the output of my IMU (in the USB2AX Pro) to estimate body attitude, and ground height at each foot.

The pots will be read by one of my new Dxld Dynamixel device per leg.

It should end up at around 480-500g with a 1200mAh 2s1p lipo battery, ssslidar and everything plugged in.

[Zenta]

Very nice project, creative and looking good!
I like your setup with the springs and pots, they should give the bot good compliance in the joints. Nice feet, looks like you used a rubber wheel/roller of some sort?

Looking forward to see it in action.

[Xevel]

Thanks all


The feet are actually one wheel, which is the smallest and softest T40 Banebot wheels.
All of them are made from one wheel, first cut in two along its natural plane to make two thinner wheels which are then cut again along the prologation of opposite sides the hexagonal hole, to get to that shape.

Each foot is, at that stage, around 2g (1g is lost in the cutting process done with a cutting wheel and a Dremel).



The surface of the leg that is in contact with the foot/wheel has the shape of a half-hexagon which mates with the remaining half-hexagon of the foot/wheel (this leg is an old "two-parts + carbon rod reinforcement" design, back when I did not trust the support structures my Up Mini! makes - which is no longer the case).




In the end I make a small tapped hole in the black part to put a nylon screw in te inside of the leg, just to lock it into place, and which does not bear any of the weight/impact.



Banebots wheels are the best for good traction, I had already used them for my Xachikoma robot a few years back.