Hacker News Reader

Comment by giantg2 | Hacker News Reader

I wish they had some examples of what RPM, torque, weight, and size specs were for a few possible applications. They seem to emphasize low RPM, but is that 200 RPM or 2000RPM? With other electric motors being capable of 10k-20k RPM, the "low" RPM mention is very vague.

If it's capable of up to about 3000 RPM, and it doesn't weigh too much it could be interesting as an ultralight aircraft power plant.

View on HN

It's an electrostatic motor, so expect peak performance at close to 0 RPM. It probably won't work well at 1k RPM, but whether "too high frequency" for it is closer to 10 RPM or 100 RPM isn't clear.

There's a video with some waves in unlabeled axis. I didn't watch it.

Anyway, it's almost certainly not aimed at aircraft propulsion or power generation. You may want something like it for robotics, but last time a paper from them circulated around here, they seemed to be focusing on instrument actuators and chip fabrication.

Their applications pages mentions wind turbines and automotive applications and promises increased efficiency vs conventional motors. That would require maintaining 90%+ efficiency at well over 1k RPM. But no specs anywhere, so hard to tell whether this is real.

I don't think it was really for automotive applications. It said something like "low speed vehicles". Made me think of something like golf carts or maybe ATVs. Of course without a gearbox, the biggest factor would be what wheel diameters are used since that would be the main ratio with revs per mile.

TBH, I didn't think about low rotational speed wind turbines. Yeah, it may be a big thing for those.

"Electric drivetrains" can mean anything from an excavator moving at 5km/h with 3m large wheels in a frequency of less then 0.2Hz up to extreme race RC vehicles, at 100km/h with 5cm wheels at ~100Hz. A car wheels go barely over 1k RPM, but I don't really expect them to do anything useful for those.

automotive application can mean as well use as windshield or wipers motors

1k RPM for wind turbines? Is that the usual gearing ratio? Is there any reason to maintain that gearing for a different rupe of motor? From my observation of wind farms, the blades spin well under 1 Hz (<60 RPM)

3000 rpm would also be good for normal aircraft, and incidentally, centrifugal pumps, assuming the torque is good enough

Another page on the site gives 500 RPM on the high end.

https://www.c-motive.com/about/faqs/

The docs say 90% efficient from 0 to 500 RPM. I wonder if that's driven by marketing wanting to print a high efficiency number, or something else.

I suspect the gap between the plates needs to be kept small to keep forces high (force is something similar to 0.5QV/d), giving high viscous losses that would increase with RPM (proportional?). I suspect that's what eventually limits the speed.

Reply on news.ycombinator.com