Rotor identification?

[BrianInVa]

Where did that bendix originate? Is it custom?, the motor looks like a standard Turnigy brushless from a decade or more ago.
You can't use a Rheostat, you will need a brushless motor speed controller with something like a servo tester to provide an actual knob to control it.
I am curious if that bendix was custom made, it looks fairly light compared to the "Cut Off" automotive versions.
I would have used a cog belt rather than the drive chain, but it is nice and compact.
I don't think you need as much battery as you are getting.

These are the parts which I ordered that were recommended to reconstruct Larry Neal’s original Butterfly Ultralight prerotator system:

 

[Sv.grainne]

This is great to know!

This Butterfly Ultralight originally came with a prerotator with brushless motor that ran on Lipo batteries and was capable of 220 rrpm.
View attachment 1162356

The frame I picked had everything stripped from that assembly except the bendix and mount for the brushless motor. Fortunately I found a former Butterfly Ultralight owner, a retired machinist in the aviation industry, who helped develop that prerotator and he still has all the documentation and photos.

He said one fully charged pair of 5s 6000ah Lipos was good for at least five prerotations, and it was rheostat controlled for soft start up and gradual rrpm increase.

So with his assistance I’ve already ordered a little more powerful 36v brushless motor, which will reach the same 220rrpm but a bit more quickly, a set of 8400ah Lipos and all the other hardware and software to make it work again. He even offered to help assemble all the hardware and electronics if I run into trouble.

Check out your battery specs, a 5sec rating for a battery is not generally given in AH (amp hour capacity).

 

[BrianInVa]

Check out your battery specs, a 5sec rating for a battery is not generally given in AH (amp hour capacity).

I know nothing about RC motors, controllers or Lipo batteries myself. Fortunately I’m being advised by one of the guys who helped develop this prerotator with Larry Neal and he has copious documentation and understands the present day equivalent for the necessary parts. So I just ordered what he recommended. He said I need two 5s Lipos with 100c 6000ah minimum and I ordered two 5s with 120c 8400ah batteries for a wide margin.

 

[Aerofoam]

That all looks good, the speed controller lets you soft start so the starting amps wont be ridiculous.
The servo tester generates the pulse signal that the speed controller is looking for.
5S is sort of an oddball pack, 6S is more common. I don't think you need the increased margin going to 8A batts.
How many spin ups do you really need per charge?

Is that bendix/mount assembly still available? I would skip reinventing the wheel if so.....

 

[Sv.grainne]

I know nothing about RC motors, controllers or Lipo batteries myself. Fortunately I’m being advised by one of the guys who helped develop this prerotator with Larry Neal and he has copious documentation and understands the present day equivalent for the necessary parts. So I just ordered what he recommended. He said I need two 5s Lipos with 100c 6000ah minimum and I ordered two 5s with 120c 8400ah batteries for a wide margin.

mah, not ah, really big difference!

 

[BrianInVa]

mah, not ah, really big difference!

lol! Yes, as I said, I know nothing about electronics/ electricity.

The listing is clear but I misquoted it.

 

[BrianInVa]

That all looks good, the speed controller lets you soft start so the starting amps wont be ridiculous.

Yes, but the prior Butterfly Ultralight owner I’m talking to said he’d still hand start the rotor before kicking in the prerotator so it’s not a jolt.

Is that bendix/mount assembly still available?

Not that I’m aware of. It’s the only part of that prerotator assembly the thieves didn’t strip off this Butterfly frame I purchased.

 

[BrianInVa]

That electric prerotator system was from Larry Neal…..and yes…..it could hit over 200 rrpm.

Although I think the rotor on his Ultralight model itself was fairly light and smaller than the 24’ RotorDyne I’ll be using, so it may not get to as high an rrpm.

 

[Aerofoam]

Just giving it a push or 2 to get it moving should be enough.