Arcbotics Build

Building the Hexy


Behold the Hexy, by Arcbotics!


According to the instructions, this build takes takes 4 hrs. It took me about 2 days, working 8 hrs each day (with breaks).  The primary slow downs were the servos, which I will detail below.


1. Some of my servos arrived broken.

a.  I took a few apart to fix, and others I replaced. You get a bag of spare servo parts, but they are not always fixable. To test, I slipped a spare servo horn over the spindle and rotated back and forth.  If it moved quietly or did not hit full range of motion, I put it aside to investigate.  Working servos make a gear winding sound.

b. Some servos broke later during attachment to the servo horns.  I went through about 7 out of 17 servos counting pre-broken and accidentally damaged.

2. The many challenges of servo horns:

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a. Getting the screws into the plastic is difficult.  You must prepare the horns by partially screwing in all the screws against a sturdy surface.  Otherwise the screw will deflect off the plastic, since the holes are very small.  This takes a long time. The screws must be turned very slowly, otherwise you risk stripping them.  You also risk having the screwdriver slip. A larger screwdriver would help.


b. The plastic is likely to break.  The screws chew up a lot of plastic and create a weak point. Luckily if they do snap, it usually happens before you go to attach the servo.  But not always.

c. Servo horns sit loosely in the acrylic. The horns are attached with self tapping screws, however the mounting holes are too big for them.  After several failed attempts, I created a fill out of tissue paper twists soaked in superglue.  The screws bit in and held.  However, doing this means the horns are very difficult to replace.

3. The acrylic pieces screw together around the servo, which means they fall apart if you need to replace or recalibrate it.


a. The way the pieces join, you occasionally need a helping hand to screw them together.  Especially when the nut must be slid in after all the other pieces are in place, otherwise it will just fall out.

b. It is very common for the servo to be inserted into the horn at the wrong point in its rotation. But you can’t tell until you have screwed all the pieces in around it.  If it is wrong, you have to take off all the pieces, move it, then screw them all in again.

It arrives centered, but it is common to have it slide out of the horn while testing it.  If this happens, you can plug it in to the Arduino and turn on the power, which will recenter it.  Or you can rotate it with your hand and judge it by eye.  But you may have to do this multiple times, each time scraping out the spindle mount on the plastic horn until it no longer holds.  Then you have to replace the horn.  They do not fit flush into the provided horns – the horns only go about halfway up the spindle mount.  This means they frequently slip while you try to screw everything around them.

c. The provided screwdriver is good for the servo mounting screws, but not the pieces that hold together the acrylic.  Those need a size 2 Philips, and the provided driver is a 1 or 0.

I estimate I spent about 20 minutes on each servo horn for initial prep and install with glue, and another 30 minutes on every servo as I screwed it into place, tested, took all the pieces off, recalibrated, and put all the pieces on again.  There are 17 servos, so I spent 850 minutes or about 14 hours on just those.  It would have helped to have a small paper printout of the leg wiring.

4. The body warps.  The braces for the body slot around the servos, but if some screws are tightened more than others, it will warp the thin leg mounts.  When the legs rotate, the corner of the acrylic leg can catch on the body plate.  The leg pieces need smaller corners, and the body needs more spacers.

5. The board might warp. If one side is over tightened it can break the traces.  The screws are very short, so they can only be turned a few times – with use, they might loosen and come apart. More spacers and longer screws would make a big difference.

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6. Some of the acrylic pieces snapped when I screwed into them, and some were not 100% laser cut so I couldn’t use them.

In summary, I would carefully consider:

The plastic servo horns which are easily damaged.

The size of the mounting holes and the use of self-tapping screws on parts which may need replacement.

The size of the provided screwdriver.

The number of spare parts.

The fit of the parts around the servos, ideally they could hold together and let you quickly swap the servo out.

The use of additional spacers for the body and control board to prevent warping and catching.

The order and time required for assembly.

Adding a pin out reference to the kit.

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