Motor change in Hellcat

[Dewey H Lee]

Hey everyone
Just sitting in my hospital room and was debating on changing out the motor in my Dynam F6F Hellcat before I even maiden. I was thinking of changing the 3720a-500kg to the 3720-650 and have questions. First will I still be able to run the same esc. If not that's no problem because I do have another but the one in the plane checks out okay after resetting to factory defaults.
Second will I still be able to run the same prop or will I need to change this also. I will appreciate any information on this matter. Thank-you.

[OV10]

Dewey,
I think your bump up in kV's by 150(500 to 650) on a 4S power system is quite aggressive.
By the numbers your max RPM's will jump from 8000 to 10400 which you may think this will be great for higher performance speeds but as the RPM's increase so does the power it takes to rotate that 13x7x3 prop. Power calcs are not linear when it comes to figuring appropriate kV motors for various blade count, diameters and pitches. I'm guessing that the 650kV motor caught your attention because it too spins a 13 diameter prop on the Dynam Waco but that prop also is only a 2 blade with a 6 pitch. Both the Waco and the F6F of Dynam do use a 40 amp ESC and that is because the kV's are matched to the props. Without a doubt the 650kV with that 13x7x3 prop on the Hellcat will most likely need something like a 80A ESC. You start messing around doing arbitrary changes without doing the power calcs and verifying with a power meter could/will lead you down the road of frustration.
I did some power calcs and the stock F6F setup uses approx. 36 amps peak power. Now if you put that 650kV motor on, your power requirements just jumped to almost 78 amps. Now even if you change to an equivalent rated ESC, can the motor deal with that new power draw before it lets out the magic smoke?? There in lays the bane to a lot of us modders is the lack of specs for ARF motors. If I was in your shoes looking for a little more omph from the Hellcat, I would be looking for a motor in the 550 to 600kV rating.
Here's a potentially good start and affordable, it is a FMS 3648-kV600 that is used on the FMS Stuka using a 13x9x3 prop and only requires 60A ESC.

https://www.motionrc.com/products/fms-3648-600kv-motor

Good luck with the upgrade decision and please get a power meter if you are going to be doing power mods. Here's a good one.
https://www.motionrc.com/collections...power-analyzer

Best regards,

[Dewey H Lee]

Thank-you OV10
I knew you would come up with facts. I'm still not real accustomed to electric flight yet and it is great to have someone with your credentials to guide a person through a project that could cost them an airplane. Electric motors an esc's still escape my knowledge. I've looked for ways to match the components on the net but anything found never really explains how to get to a conclusion and most of the time starts getting way over my head. Spent 20 years running an experimental machine shop, a video jet printer repair shop, and a kp propellant pressure filler repair shop as well as taught 2 classes on the kp equipment. But still nothing takes the place of experience and background. It just so happens that I have a 3648-600kg motor laying around that I had posted a while back to find out what would be a good platform to put it in. The only thing I'll have to get will be a 60 amp esc. I have a detrum 50amp that came out of a dynam Pitts. Don't suppose that would work. Anyhow hopefully motion will have esc's back in stock soon. Then I'll give this a try. Thank-you again OV10 and I will order the watt meter at the same time as the esc. BTW do you anticipate a the motor change will require changing out the mount or board. That is one reason for the motor I mentioned. It had. The same frame and dimensions as the one in the plane. Just a higher kv rating. Detrum also carries a 600 with the same dimensions.

[OV10]

Dewey,
Anticipation is a line from a Carly Simon song.....HA:rolleyes:. Seriously, trying to advise on the mechanical fit up of one brand of motor into another manufactures airframe is a crap shoot and sometimes in all practicality becomes a trial fitting process. Even parts from the same brand it can become a mod to fit activity. I have the specs for almost all the FMS motors that is why I recommended what I did for electrical but not mechanical. I guess you could put that Detrum 600kV in with a higher rated ESC and then do some power measurements and monitor if the motor heats up to a melt down. I literally mean "melt" because that is the prime failure of the motor by drawing more current than what it is rated for, the adhesive that holds the magnets in the motor de-bonds.
Have fun with your first power modding experience but be safe when doing so.

[Flygirl]

Thank-you OV10
I knew you would come up with facts. I'm still not real accustomed to electric flight yet and it is great to have someone with your credentials to guide a person through a project that could cost them an airplane.

He knows his stuff!!!

[Dewey H Lee]

I have never doubted him for a second😁.

[AkumaZeto]

I put the motor from the dynam pitts in my cat. Smoked the stock esc right before landing lol. Changed it out for a 70amp unit and now this cat can go back in time it is so fast.

https://www.motionrc.com/products/dy...FQwPaQod_rsMLQ

http://www.masterairscrew.com/collections/3-blade/products/3-blade-13x8-propeller

I also use a master air prop!

[Dewey H Lee]

I've got a 3720a 650kv that came out of the Pitts by dynam that I had with the esc. Is that the one you had. If so what size prop were you smoking on it.

[Dewey H Lee]

Dang now that's to funny. My phone changed spinning for smoking.

[Dewey H Lee]

I am sorry AkumaZeto I should read more carefully. I see you already have it posted.

[Dewey H Lee]

Yes crap. I have the a and not the c. One of the biggest problems I had with that plane was spinning the prop and collet off because you couldn't get it tight enough with that spinner.

[AkumaZeto]

Still working on the flux capicator for this bord. With the 1.21 gigawatts of power it now has and all...Mr Fusion might be a good thing.