Sheared Bolt Head (fixing it and I hope preventing it happening again)

So, lets see how this goes:

Video Part 1

So, about extracting that bolt it didn't go down without a fight ... but I won.

First I tried the "proper way" and drilled it and used an "Easy Out" ... sadly that didn't work and the fucking thing broke in.

here you can see the broken tip of the "Easy Out" and the mangled end of the bolt which came out "the old fashioned way" by brute force. Yep I was able to get clearance between the gooseneck and the bolt and do it with "vice grips"

This time on this battle I fought the law (friction) and "I won".

Now when I took the bolts out I saw that the primary problem was that the heads of the bolts were not given an even surface upon which to grip (thus dis-advantageous forces could be brought onto the edges of the bolt head). This is evidenced by the shitty crapy washer that was used:

So, suitable for a pie tray, but not in this sort of environment. Now I've used double (and better) washers. This will mean that more even pressure will be applied to the bolt head (reducing the chances of another "pop off").

giving the heads a good chance of survival ... I mention this aspect in the last video.

Next, while I had the need to pull the headset off to get at that bolt I thought I'd show you what it looks like (hopefully you'll never need to see it). I'm quite impressed.

This design is actually very sound as it will enable the system to fail gracefully and safely should one or more bolts fail ... this is because the design will cause the front bolts to fail first letting you know something is wrong pretty quickly while having the remaining two still hold shit together. Very nice.

Analysis Segway

Lets just segway off here on a quick analysis of this design: as you can see the back of the gooseneck holding the steering bearing is strongly supported at its back by large flat bit of cast metal against large flat bit of cast metal cast and held down from movement with 4 bolts. So referencing that above close up picture of the neck out, lets look at the angles of force here.

Principally there are 2 directions of force that the mount can take, one is the transfer of road impacts the other is the riders weight (and of course momentum changes which effect what your weight is).

The shape of the gooseneck and its "keying in" to that slot to the anchor points means that the road impacts (the fastest shocks the system will experience) are taken against that pair of thick cast pieces, not on bolts. This means there can be no mechanical wear from stress ( == a good thing).

Next the weight of the rider pivots around that angle shown above and has an amount of leverage (the length of the straight red line) but because of the way the mechanism is seated the only bots to take significant load are the front two anchor point bolts (orange). These will be under tension only, which is good because shear is what scissors do (... which is why we call them shears) and bolts have much lower shear strength than tensile strength. Keep that in mind when reviewing the "basic kiddy-level" (seriously no engineer would be comfortable with this after first year) engineering on the (quite high powered and fast) Zero 9 which failed below.

No wonder it failed ...

End Segaway ... 

Anyway at the end of all this it looks like this (with the double washers) and is now test driven and back on the road.

Lastly I took this opportunity and pulled the belly pan off the Dual Motor and inspected that. Its interesting how different that is in assembly:

They have "double washered" the leading edge AND used spring washers AND used lower tensile strength bolts. Now this may seem like a "bad thing" but actually its possible this is a good thing. You see that lower tensile strength bolts are less "brittle" and thus inclined to stretch (or bend) before just snapping.

So maybe what's happened here is that my Single Motor Mercane is an older one and they've just dressed it up to look like a 2019 (with the key operation) ... perhaps they've learned about what's better (by observing failures) and adjusted accordingly.

Either way now both are fully operational, I understand (and I hope by sharing this you do too) more of what I need to keep an eye on with my scoots and things will go well from here on in...