I was concerned with the chain action on the Enertia I’m testing when it’s pushed around unpowered. It felt like what happens when a chain and sprocket get really worn- very close to the point of breaking- on a gas bike. I wasn’t all too concerned, as soon as you put the power to it, it rides nice and smooth.
I got a great explanation from the guys at Brammo, it turns out, as I’d hoped, it’s the natural characteristic of a PMAC motor. Here’s the video showing the effect:
Here’s the explanation:
(The Enertia has) a synchronous permanent magnet alternating current motor or “PMAC motor”. This type of motor has strong rare-earth magnets bonded to an internal rotor, and the copper-wound stator is external. When the motor is not powered, and the rotor is forced by external motion, the magnetic reluctance path is closed as the magnets pass by the stator poles.
This reluctance path tries to hold the rotor in place and this effect is called “magnetic cogging”.
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Wow… I don’t think mine does that, but now you’ve got me wondering. So is that happening because the chain is wanting to stay stuck to the sprockets closest to the motor (due to the magnets)?
No, it’s just happening because the motor is resisting turning when there’s no power. It’s just a side-effect of the motor type, and no cause to worry about anything…
“…no cause to worry about anything…” ??? LOL.. you can only worry about losing your INERTIA really fast!!
I got an EV push bike (http://vipglobal-asia.blogspot.com/) and I can remove the electric power, and the bike keeps going, and it never gets such a drag!
Congrats on your bike, I hope it’s as much fun as it looks. As for this cogging effect, the PMAC motor is one of the most efficient configurations available. At slow speeds the cogging is noticeable, but it doesn’t cause enough drag while you’re riding to even hint at any motor braking.
So strange… mine doesn’t do that.
Do you happen to know if your bike has the Perm PMAC motor Harry? I wasn’t aware that they used different motors, but there’s a lot of stuff I’m not aware of.
The other point here is that the slapping is minimized when the chain is tighter vs. looser. I never checked to see if the chain was running a little loose or not… If so, it should be touted as an “automatic check your chain, bunky!” alert indicator.
I don’t know the answer to they Perm PMAC question, but I assume they use the same motors in all their Enertias. How many miles on that bike? Mine has only 300.
crap, I didn’t check. and. I HAD TO GIVE IT BACK >sob sob<