Saturday 21 September 2019

up the steep bits

I'm always one to be interested to find where the limits of things are, so naturally I wanted to test the Mercane up the steepest long ascent in the area, so I picked this one


My GPS shows that its a bloody steep climb


and you can tell by the drop to walking speed about a kilometer after starting back that something happened!

Yep, I found not the limits of the motor and battery power, but of the brakes!! On that steep descent trailing them relentlessly caused the disc to overheat and I had to walk back most of the way (easier down than up I suppose!) or risk brake failure.

Here is my gopro footage of that.


so ... now I'm wondering about how to use the regen brakes capacity which I understand is in the in the controller in concert with the disc to perhaps get this little baby to its limits.

Or maybe accept that I've pushed it past where it was ever thought of that it could go ;-)

PS: an interesting and worth while read for the brake novice is here: http://www.epicbleedsolutions.com/blog/how-hydraulic-brakes-work/

I'll quote the relevant point about brake fade:


Pad Fade

All friction material (the stuff your pads are made of) has a coefficient of friction curve over temperature. Friction materials have an optimal working temperature where the coefficient of friction is at its highest. Further hard use of the brake will send the friction material over the optimal working temperature causing the coefficient of friction curve to decline.

This high temperature can cause certain elements within the friction material to melt or smear causing a lubrication effect, this is the classic glazed pad. Usually the binding resin starts to fail first, then even the metallic particles of the friction material can melt. At very high temperatures the friction material can start to vaporize causing the pad to slide on a layer of vaporized material which acts as a lubricant.

The characteristics of pad fade are a firm, non-spongy lever feel in a brake that won't stop, even if you are squeezing as hard as you can. Usually the onset is slow giving you time to compensate but some friction materials have a sudden drop off of friction under high temperatures resulting in sudden fade.


Green Fade

Green fade is perhaps the most dangerous type of fade which manifests itself on brand new brake pads. Brake pads are made of different types of heat resistant materials bound together with a resin binder. On a new brake pad these resins will cure when used hard on their first few heat cycles and the new pad can hydroplane on this layer of excreted gas.

Green fade is considered the most dangerous as it can catch users unaware given its quick onset. Many people would consider new brake pads to be perfect and may be used hard from the word 'go'.

Correct bedding-in of the brake pads can prevent green fade. This process removes the top layer of the friction material and keys the new pad and rotor together under controlled conditions.


I hope you found that helpful.

2 comments:

CB said...

Found this post looking for regen braking info on the mercane widewheel. Were you ever able to get that working? Any tips?

obakesan said...

CB

no, I've not put time into getting that working, but I also have less motivation to do so. I recommend you pop the swing arm side cover off your scoot (any one will do) and then take off the nut (or at the very least put a spanner on it and see how much it turns before the bolt which is the axle turns (remember leftie loosie). I recommend you do this because you can see how much twist there is in the keyway for the axle (which is not round but has squared off sides).

This is because the only way that the wheel provides ground force is if that axle is held captive. If it chews out sufficient metal and can spin then that's a "very bad thing" and will esssentially destroy the wires (thus destroy itself).

You see under regen braking the axle takes force in the opposite direction (unlike regular braking where the disc & caliper takes the force not the axle). The constant twisting back and forward (with a motor of higher power than the little widdly winkidink 300W scooters) will over (probably a short time) chew out the cast aluminium of the swing arm (note its square sides where the axle sits) or at the very least contribute to the axle nut becoming loose (because I doubt you've removed it and put thread lock on it like Permatex that I appear to be evangelizing).

:-)