Friday, June 3, 2011

Isle of Man - Day 6.5 - Noise from the motors

(By Lennon)

Mark had left by the afternoon (he's gone until Sunday - friend's wedding in Germany), and we were just about to kick back, relax, and wait for the first qualifier/practice on Saturday. We've had an intense week, but everything has checked out just as planned.

But I wanted to do one more speed test to ensure some adjustments we made to the motor controller were effective. Initially I was going to just go by myself - just a few quick passes at 100MPH out on our country road circuit. But Radu ended up catching a ride with Allan's friend - since it wouldn't hurt to have some tools out there and an extra person just in case.

When I was doing my final 100MPH pass I noticed a very faint rubbing noise when I was manually pushing the motorcycle to turn it around. I am so sensitive to noise when riding the bike, and it was clear that something was wrong. Hopefully just a fairing rubbing or something.

So I slowly rode the bike back to Radu and he crawled around the bike with his ear and hands as close as possible to the various parts of the bike. I (in full rider gear/helmet/gloves) rolled the bike back and forth over the point where I heard the noise. Radu was equally puzzled. It was very faint, but there. With 100MPH speeds and 32kW of power, a small rubbing at low speeds could domino to extreme rubbing at high speeds when centrifugal forces and heat can cause items to expand. The expansion would make the rubbing increase, the point of contact would get hotter, make it expand more... u get the point - it's a runaway affect that is an engineer's nightmare - totally uncontrollable and would happen very fast. The motor would likely overheat, melt, and the rider would hopefully feel the drop in power and be able to decelerate before the motor completely tears apart.

There are two things spinning on this bike, and they spin at different speeds/frequencies: (1) wheel and (2) motor. First Radu had to figure out if it was caused by the wheels rubbing (maybe on the fairings, etc.). Nope, the rubbing didn't occur at the rate of one tire revolution. Now to the motor. Move the bike and watch the motor shaft. Yep, we heard the noise every time the motor spun around once. So it's something in the motors.

Radu is a wizard, and he has spent a lot of time with our motors - going all the way back to the dyno tests which started in February. He worked with ninja precision - and noticed the gap between the rotor (rotating part of the motor) and the magnets (stationary part) were extremely close. He grabbed a few wrenches to see if some of the internal bolts were loose. They were!! The noise went away when we tightened the bolts. This was a fault of the motor manufacturer, and so is the rubbing. It shouldn't do this. Thus in conclusion: (1) the gap between the rotor and magnets was incorrectly set in the factory - it's too small (the gaps on both sides of the rotor should be the same, but it is not). (2) the motor manufacturer didn't tighten the rotor bolts properly - and they slowly worked their way loose over the last few months. The lack of a gap and loose bolts were causing the rubbing noise - we were pretty sure.

So I drove slowly back to the shop, while Radu and Allan's friends followed. I wanted to repeat the noise: we loosened the bolts - the noise returned. We tightened the bolts and the noise went away. OK - conclusive - that's the problem.

So what do we do? Our options:

1) Ignore it - might not be an issue now that the bolts are tight. Risk: the small gap might make the motors over heat and rubbing could cause thermal runaway (as described above).

2) Replace the motors (we have spares). Risk: this requires a total bike rebuild due to how our motors are bolted to the frame. Taking the bike completely apart two days before our qualifier is riddled with land mines.

3) Rebuild the faulty motor. We can do this with the motors left on the bike (i.e. we don't need to disassemble the bike). Risk: we've never done a full overhaul rebuild. Do we have enough time to ensure the motors are properly working after the overhaul? If something goes wrong - we'll have lost precious time and it would be a rush to swap in a new motor.

None of these seemed like great options. Each with their own risks/uncertainties.

In the mean time we went and chatted with a local Manx team who is racing for the third year. They've had these motors blow up before - and might have good advice.

After much deliberation, we decided to go with #3 = rebuild the motors. If we couldn't pull it off in the few remaining hours of the night, then we'd make a go-/no-go in the morning. We would then have to rush to pull off #2.

So Radu started taking the motor apart. One thing you should know about Radu. He is - what we call in engineering - a beast. He works best under high pressure and risk. Extremely powerful if contained. He's the guy you want on the airplane if it's going down with one minute to spare. He'll figure out some way of strapping himself and other parts to the wing - or whatever - to ensure the plane banks, dives, etc. into a fairly safe landing. When he's in "beast" mode, his eyes become large, he becomes quiet/focused (though he might blare out a classic rock song lyric or two on occasion), and you can tell he's in an arena where he thrives. By picking #3, I knew the Radu beast would come out to play.

And it did - here he is working on the motor:

With the motors open it became clear that we likely just avoided a catastrophe. Very little to no damage to the motors, so we must have caught it the instant it started. It is unlikely that Allan would have heard the noise - since he only knows one throttle position (full), and is not sensitive to the noises (since it might sound normal to him).
Some pics of the motor as we took it apart:

We removed three shims that were on the inside of the rotor on the shaft. This should balance out the gap on both sides of the rotor.

Motors have very strong (rare earth) magnets, and it's a very delicate/tricky procedure. As the outer stator cover (magnets) are brought in close to the disassembled motor (as shown in the pic above), the entire assembly wants to crush in on itself because of the magnetic forces. If your fingers are in between they'll certainly be crushed and possibly removed free of charge. I busted out a wood saw and cut three wooden wedges to slowly bring the outer stator into contact - hopefully flat, level and in control/steady. After a few modifications - and a bit of the Radu beast - the motor came back together.

When we decided to rebuild the motor, our conditions were that it would need to go back on the dyno for a full pack, full power test. If it passes, we'll fully recharge the pack (4 hours), and go out on the road for testing in the afternoon/evening. If it doesn't pass... we have a dilemma.

We were in bed by 1:30AM. I woke up at 6:30AM to come back to the shop and charge up the bike. Due to another incident (which we fixed), I didn't feel comfortable letting it charge over night.

Let's hope we can obtain access to the dyno & the repaired motor passes the test.


  1. Good job catching that issue before it was too late. Did you add Lok-tite to the loose bolts?

    Waiting for a positive update...

  2. Reading the blog the last couple of days has convinced me the race is not to be missed. I've got leave from my very understanding wife (and work), booked my flight and will be arriving on the island the Tuesday before the race!

    Great news about the fix, be good to see how it goes on Saturday.