Benifits of Comet Torque converter

[winchmeup]

Ive just spent the weekend playing with an old gokart at my inlaws farm.
It has a 6.5hp honda clone motor with Comet torque converter.
I had forgotten just how impressive the difference the converter made. It took it from not being able to spin the wheels from startoff to being able to leave a short burnout on cement. Also the top end was greatly improved. Throttle responce was also pretty impressive with no real slip noticable at all.
Having read a bit of the high speed guys quest for power. Has anyone tried one of these?
I have no idea what the ratios are but it could soften some of the startoff problems and give more top end.

 

[Jeremy Harris]

These things suck a fair bit of power, making them less efficient than a chain or toothed belt drive by a fair bit, which would give a big hit on battery life.

They work well on petrol engined stuff, because those engines have zero torque at zero rpm. They don't really give a benefit with a PM electric motor, though, as an electric motor of this type can deliver maximum torque over pretty much its whole rpm range. This means there's no real merit in using a torque converter, as there's no need to compensate for the changing torque with rpm characteristic that petrol engines have.

There are some small advantages in terms of reducing the demand on the controller at low rpm with a low inductance motor, as those who've played with variable scooter-type drives have found, but the losses are still pretty high and, IMHO, this alone makes them of doubtful real benefit over a fixed ratio drive.

 

[winchmeup]

thanks jeremy
i would like to read a bit on peoples experience. do you have a link to the scooter-type trial you mention?

 

[Jeremy Harris]

A quick search (using the forum search facility at the top of the page) gave these threads:
http://www.endless-sphere.com/forums/viewtopic.php?f=12&t=17576

http://endless-sphere.com/forums/viewtopic.php?f=10&t=38598

that should give you some ideas.

 

[John in CR]

I had one on my lead pig electric motorcycle that was my first EV attempt and it did it's job. The problems are that they're big and heavy, and they're made for ICE rpm engagement. Efficiency-wise Comet claims something like a 6% loss, so they're more efficient than NuVinci's. Plus they're cheaper, can handle more power and torque, and the shifting is automatic.

Engagement is handled by a centrifugal clutch at something like 1200-1500rpm. I took the springs off the weights on mine for instant engagement so it was noisy at low speeds with the weights rattling around. The 600lb lead pig was just too poor a performer, so it just took it for a few rides and hacked it up. I never did try low strength springs in the clutch to get rid of the noise.

The pigbike climbed right up the 25% grade immediately upon leaving the driveway, and there's no way the 3kw motor would have done it without the Torq-a-verter without gearing it ridiculously low. The size and weight though meant that I could have easily added a helper motor geared lower for a better result.

With a rig something like a pair of big RC motors, and install the pulleys directly on the bike, it has potential to be useful for a high powered where you want your motors out of low efficiency operation before they see load. The CVT part of it seems to be much better than those on scooters, so dismissing it as useless for electrics I think is a mistake. You just need the right application such as mountainous trail riding, or pulling heavy loads, where multi-speed is really needed despite the wide torque band of an electric motor. The efficiency curve and 0 efficiency at 0 rpm can be an important consideration for electrics too.

John