Fightercat Cheetah motor question

[larryrose11]

All,
Im going to build my first cat, a Fightercat Cheetah Im getting fom another member.
I was planing on using a TP Pro Comp 4060 2100kv motor.
Here are the stats:
4200W 4-Pole Brushless Motor
40mm x 92mm can
Max amp 242
Max volt 26v
Max rpm 50k


So, my question is about voltage,
Is running this motor on 6S potentally dammaging?
6S fully charged is 22.2V, Which will drop with even a little bit of load.
The motor say's its rated for 26V, 50K RPM
22.2V * 2100kv = 46620 RPM, @ 100% efficency
Will I be outside the usefull range for avalable props, somthing like a x440 or so?
I allready know Im crazy, but what would be the downside assuming I keep the temps in check??

[Alexgar]

5 s maybe a couple of 6 s fun runs but your amps will be through the roof provided your batteries are up to the task. Btw 440 sounds a little small to me for q 34" hull I run a 442+ on a 32" hull

[larryrose11]

The OSE speed calc suggests 70 MPH on a x440, (2100 KV, 90% efficency, 6S, 20% slip, which I calibrated to measured GPS values from another users results)
which is going to be too much unless the setup is finely tuned.

[madmikepags]

I wouldn't go anywhere near that Kv on a 6 cell setup 1200-1600 is enough. with my Neu 1527/1Y 1250Kv I can get well into the 60's for 4 minute offshore runs on 50-52mm props can go even bigger or pitch up the prop for more speed.

[Fluid]

It all depends on how you want the boat to run. Listen to Mike. You are assembling a SAW boat. Setups like this do not allow long run times, just a few long passes then back to the beach. I used a similar Kv motor on 6S to set several SAW records in the high-80s with a 32" cat, but two-three passes were all I could make before temperatures began to approach critical. Average amps were in the 250-300 range, and no amount of cooling will keep an ESC below critical for very long without cooling off periods. A hull that size will be more efficient with props in the 45-50mm range. If you used a 40mm prop slippage would be high, might as well use a lower Kv motor and a more efficient prop.

BTW, 6S is 25.2 volts fully charged, not 22.2. How much voltage depression occurs depends upon the actual load and on the quality of the cells. The ThunderPower 65C cells I used in the above boat dropped to around 20.6 volts under full load. I have a similar TP4060/5, these motors' actual Kv will drop dramatically under high loads. You can expect on-the-water rpm to be in the 39,000-40,000 rpm range. Even then the setup is hot enough to cause you problems if:

- you prop just a little too big
- you run for just a little too long
- the water conditions change just a little
- the boat runs just a little too stuck down

Do what you want, but I'd recommend either go to 4S with that motor, or choose a motor with a Kv around 1500 on 6S. That is not a SAW-type hull and it will trap a lot of air risking a blow over. The TP4060/4Y or TP4060/7D would be better 6S choices and will still get you well into the 60s with a safe setup.


.

[larryrose11]

madmikepags,
It is the "why" that Im after.
For electric motors, lower speed typically draws more amps because of less back EMF. Lower speed can also produce higher torque, which allows the use of a larger prop. I’m looking at is from the other point of view, higher RPM, smaller prop, lightly loaded.
Is there a problem with running a nice prop at these kind of speeds? Are there other ramifications I’m missing? Im sure there are.
Remember, conventional wisdom or common sense is based upon something familiar, factual or not.

[larryrose11]

Fluid,
This is the kind of info Im looking for.
Relation of hull and the prop diameter, prop slippage, and the like. I know that this hull can be an amp hog if it runs too wet.
Thanks a lot for the knowledge!

[madmikepags]

Fluid is correct in everything he said, hulls like certain size props, so you aim for setups that will facilitate those prop sizes, I also wouldn't put too much faith in a speed calc. They leave out too many variables. And ask around like you are, theres nothing like experience and if you can get the knowledge and experience from guys like Jay before you put the boat in the water and blow stuff up you're much better off.

[larryrose11]

madmikepags,
Fluid,
Your comment say a lot.
On the KBB forum, a builder choppertony built a cheetah for a customer. The customer wanted a 4S setup, so a Leo 4092 2080KV motor, and a T180 controller was chosen. After 3 min run time, the T180 came in hot, 165F. They ended up with a Swordfish 200, which performed better. The confirms what you two were saying about the amp-hogging with such a high KV, low voltage setup.
So, a motor with a Kv around 1500 on 6S is what it will be.
More on this later.....

[properchopper]

Hi Larry,

Just got a blip on my mental radar that my name popped up in a thread. Here's a few things (and be aware that I'm just a tiny ant in the company of folks like Pags and Jay) so take my input with some grains of pixie dust

The Cheetah I built for a customer ran a Leo 4082 2000KV on 4s2P and originally a T-180 spinning a 447/3 and was GPS'd at 57.1mph. The customer claimed @165 degrees on the T-180 after about 3 min runtime but I have a sneaking suspicion it was closer to 5 minutes. I routinely beat the piss out of the T-180 in my P-Mono without getting it that hot (with the exception of a recent heat wave). We then switched his Cheetah to the new CC marine Hydra Ice 240 which was reported to run cooler. Lovely ESC BTW.

I built myself a Cheetah shortly afterwards as a gift to myself for pure fun running. Neu 1521 1.5D 1900KV (somewhat similar to the Leo 4082 2000KV) and now with an old CC Hydra 240 (the orginal FCR 240 had a solder meltdown) and 4S2P 65C/130C Dinogy 5000's. First with a 450/3 (wheelie city) and now with a 452/2 the boat's knocking on the door of 60mph and I'm lovin' it. No GPS, just fun, fun, fun.

While many of us early in the FE maturation cycle insist on overpowering with huge motors and SAW-like overvolting to pay homage to the gofaster deity, I've learned over time to go for better balanced setups and less rescue boat time. [Not that I wasn't an early member of the ZSP-WTS Club {Zoom Splash Plop - What's That Smell ?}]


My advice after building two Cheetahs is to aim for no more than roughly 60mph. As Jay pointed out these are tunnel hulls and pack plenty of air which as you go faster has a funny habit of initiating some curiously charming aerobatics. I could easily make mine faster but I HATE rowing that darn rescue boat

This chart may help zeroing in on what's a generally acceptable safe operating zone when pairing voltage with KV

kv_voltage.pdf

Alternately, the application form for the ZSP - WTS ? Club is available online at ScrewIt/I [email protected]

[keithbradley]

All,
So, my question is about voltage,
Is running this motor on 6S potentally dammaging?

Yes, absolutely.

I have done the high RPM/small prop setups and they do work. However, the motor you have is a poor choice for this. The 40x92 TP motors have been suspect in high RPM applications, and I wouldn't expect yours to last long. A lot of the Chinese motors get increasingly inefficient at high RPM and current loads. Where some of the high end two pole motors like Lehner are most efficient in that range, trying to reproduce that with a long Chinese 4 pole motor with a 5mm shaft will likely come up short. Most people who increase the pack voltage on a 4s setup to 6s see more speed, but not nearly what they should. Efficiency is sacrificed and current draw gets excessive.
I don't know that TP would be my motor of choice for this, but if you are dead set on using them, you will have better results with the 40x82 or 40x74 size. I think the 92mm models might hold up a bit better if they were made with a 8mm shaft, but that's just speculation. It shouldn't take a 92mm motor to turn a 40mm prop anyway.

[larryrose11]

properchopper: Thanks for the chart and the info. As this is my first larger boat, and my first cat, the rules are different than my experience with small riggers.

keithbradley: Thanks!! I started this thread with a bit of hyperbole so I can learn more about the boundary's, it helps me learn. I was planning on using somthing in the 1500 KV range, as Fluid, Mike, and other pros have suggested. Something like the TP4060 4Y. I'm attracted to the TP motor because of the Neu-like details in the manufacturing, but at a lower price. I have yet to run a TP motor, so I don't have any direct experience. I may end up with a Neu 1521 1Y (1577kv) on 6S

I would love to see a through tear down of different motor types for comparison purposes to see some of the main motor characteristics, like rotor Gauss, air gap, rotor construction, stator lamination's and the like.

[Basstronics]

http://s38.photobucket.com/user/basstronics/library/RC%20Boats

I got pictures of TP Power, Leopard & Tacon.

[sampit]

I have ran mine on a TP4060 1600KV, TP4050 1450KV Leopard 4074 1400kv and a 3740 1760KV outrunner all on 6s
My hull is NO5 I pre-ordered one off the first batch, its around 2 years old now embarrassed to say,I'm still having a hard time to get it to run right with any motor, always seems to plough. I would say the COG, prop angle and hight setting are critical on the Cheetah, that experience comes with years of Cat building,, that's one think I am lacking, this is only my second ever cat

After building my first cat a Rivercat with great results I thought the Cheetah would be a doodle, boy how wrong was I!
but will get there one day.

just uploading a video in the video section with today's run, its still not right, the sound its making might be a good clue to someone, but each time out its getting better, thanks to the input from the forum
without this help I would have sold mine ages ago, but its too good looking so I will keep battling on.

[chipgibbs]

Just to blow my own horn....I broke the IMPBA 1/4 mile oval record with my Cheetah in P-Cat on Saturday 4/20/13. The build was a copy of Tony's first Cheetah build and uses a Leopard 4082/2200 on 4S2P with a Seaking 180 and Octura X545. Temp on the ESC after 4 laps was 130 and 126 on the motor.

I could not break the 1/3 mile this morning as the wind was blowing about 25mph and blew the boat over.

I'll publish the 1/4 mile times when I see the Certificate.

Chip