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Old 04-30-2014, 03:52 AM   #1
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Default DC-3 electric power

Would appreciate any suggestions for a Top Flite DC-3 which should weigh about 9.5-10 lb total. I plan to put ESCs in fuselage and lengthen wires to the motors.

Do ESCs need cooling?
What would be good motors?; have read bad things about Tower's Rimfire
Battery suggestions for 10 minute flights?

Thanks!
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Old 04-30-2014, 04:27 AM   #2
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78yes,
welcome to wattflyer,have you search the forums for electric conversion for the dc-3. esc's should have cooling. best motors to use for such a nice bird would be hackers,axie...ect..ect.

have you done a conversion before?

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Old 04-30-2014, 04:28 AM   #3
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Escs do in fact need cooling, especially the more you push them. I would get escs that give you ample play room, so if a motor draws 30a, get a 40a esc, or larger if you wish. As for motors, eflite are good, but too costly for me. I go with turnigy or rctimer.
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Old 04-30-2014, 04:28 AM   #4
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Originally Posted by 78yes View Post
Would appreciate any suggestions for a Top Flite DC-3 which should weigh about 9.5-10 lb total. I plan to put ESCs in fuselage and lengthen wires to the motors.

Do ESCs need cooling?
What would be good motors?; have read bad things about Tower's Rimfire
Battery suggestions for 10 minute flights?

Thanks!
put the esc in the cowls, and lengthen the battery cables, use 12 gauge wire up to 12" if more length is needed use 10 gauge wire, YES ESC Need Cooling Big time,

two of these motors should work great for you. use a 10 amp UBEC from Castle Creation.



http://www.graysonhobby.com/catalog/...0gsvvd2jcstir4


http://www.graysonhobby.com/catalog/...0gsvvd2jcstir4

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Old 04-30-2014, 04:37 AM   #5
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http://www.rcgroups.com/forums/showt...2090742&page=2



use 1- 8000mah lipo if you have the room for it, you might need to use 2 - 4000mah lipos in paralell, run both motors from one lipo, or 2 lipos in paralell, this should give you about 4000mah per motor, dont expect 10 mins of flight time, unless you can carry a big big battery, 8000 mah lipo/s should give you about 6 to 8 mins of flight time with throttle management

https://www.hobbyking.com/hobbyking/..._4S1P_30C.html

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Old 04-30-2014, 04:56 AM   #6
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The grayson motors are very good, but if you want the best, use 2 - Eflite power 32 motors with 60 amp esc. and use a 4 cell lipo. use a 10 amp ubec, and disconect the BEC wire from the ESC on both ESCs

http://www.wattflyer.com/forums/show...highlight=ubec

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Old 04-30-2014, 05:15 AM   #7
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Originally Posted by 78yes View Post
Would appreciate any suggestions for a Top Flite DC-3 which should weigh about 9.5-10 lb total. I plan to put ESCs in fuselage and lengthen wires to the motors.

Do ESCs need cooling?
What would be good motors?; have read bad things about Tower's Rimfire
Battery suggestions for 10 minute flights?

Thanks!
Also the Hacker and Hyperion motors are pretty good. At 10 pounds weight, you will need about 1500 watts or so. That would be 400 or 500 watts per motor.

Here is info on that Hyperion motor in one of my models.

http://www.wattflyer.com/forums/showthread.php?t=73065

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Old 04-30-2014, 12:37 PM   #8
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Actually... its better to extend between the motor and ESC than between the ESC and battery. Especially at partial throttle you can blow up the input capacitors if you extend between ESC and battery.

At 10 pounds weight, you will need about 1500 watts or so. That would be 400 or 500 watts per motor.
Last time I checked... 1500/2 = 750

DC3 should fly in a very scale manner at appx 80 watts per lb.... if its not overweight. It doesn't hurt to have more available but its not an aerobatic design.

I recommend setting up differential throttle mixing on a switch for taxi. I have done this with a different DC3 with outstanding result. With just one prop spinning it could pivot without moving the other side's main wheel. Let the tailwheel be free castering rather than steered by a pushrod if you do this. It can make the takeoff a little tricker than having a steerable tailwheel though, so you need to be comfortable handling taildraggers.
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Old 05-01-2014, 01:57 AM   #9
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[QUOTE=fhhuber;946942]
Last time I checked... 1500/2 = 750

DC3 should fly in a very scale manner at appx 80 watts per lb.... if its not overweight. It doesn't hurt to have more available but its not an aerobatic design.



Oooooops!

The DC3 does have just two engines.

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Old 05-01-2014, 02:14 AM   #10
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Originally Posted by fhhuber View Post
Actually... its better to extend between the motor and ESC than between the ESC and battery. Especially at partial throttle you can blow up the input capacitors if you extend between ESC and battery.

DC3 should fly in a very scale manner at appx 80 watts per lb.... if its not overweight. It doesn't hurt to have more available but its not an aerobatic design.

I recommend setting up differential throttle mixing on a switch for taxi. I have done this with a different DC3 with outstanding result. With just one prop spinning it could pivot without moving the other side's main wheel. Let the tailwheel be free castering rather than steered by a pushrod if you do this. It can make the takeoff a little tricker than having a steerable tailwheel though, so you need to be comfortable handling taildraggers.
Agreed on the longer wires between the ESC and the motor, rather than between the ESC and battery. This is pretty much what Castle Creations has indicated over the past years.

As for power, 80 watts per pound would easily pull your model through the air, but I don't know how the model would take off on a grass field with only 800 total Watts on a 10 pound model. Can other readers provide info on this?

Nothing worse than a very finely detailed model that does not have enough power to get off the ground. We had a club member with that exact problem with a scale model jet airplane with twin fan jets last fall. He never did get it off the ground.

For a model that has a lot of work (and perhaps a lot of $$$$) involved in putting it together, IMHO, it's not a good idea to go cheap on the motors and ESC's. Nice thing about these electric motors, you can put in two oversized motors, and reduce their power output by putting on smaller diameter props. Or, increase their power output by putting on a larger diameter prop, within the rating of the motor/esc/battery pack anyhow.

I've got a number of Hacker motors, that do the job very well. Motors in the size your model would need would be the Hacker A40-10L, or the A50-12S motors. The A50 might be a bit big. Also, the Power 46 motors look good.

I've got the A40-10L motor in one of my models. This motor weighs 9.7 ounces, and is pulling 46 Amps, 700 Watts off of a 6S A123 battery pack. This A40-10L motor turns a 14X7.5 prop at 7800 RPM. This motor can handle up to 1000 watts if desired.

http://www.espritmodel.com/hacker-a4...motors-v2.aspx

Another good motor product is the Hyperion line of motors.
http://www.wattflyer.com/forums/showthread.php?t=73065

Also, you might want to check out one of those computer programs for predicting electric model airplane performance. A good one is www.motocalc.com.

And, if you're used to performance of glow engines, take a look at this thread showing direct comparisons between electric and glow or gasser engines:
http://www.wattflyer.com/forums/showthread.php?t=73275

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Old 05-01-2014, 06:01 AM   #11
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Piper J3 Cub (full scale) has just 30 watts per lb equivalent power. Takes off from most grass fields just fine.
Change to Tundra tires and it can handle even rougher fields...

Its not just watts of power... There's also proper matching of the prop(s) and limiting the aircraft to terrain appropriate for the wheel size.

Its very easy to be unable to take off from one type of grass field and to have no issue at all on another. Not all grass is equal.
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Old 05-01-2014, 11:03 PM   #12
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Watts per LB can be misleading.....I have not bothered with worrying about it since some variables aren't addressed in the equation. I fly mainly scratchbuilt planes and use a combination of weight, amps, speed and thrust to come to a suitable powertrain combo.
For instance....I built a GWS C47 once that had the std brushed motors and small 5in props, using a small 3s 1200mh battery (for correct balance) my Wattmeter showed 260 watts being pulled at WOT. The plane was approx 1.5lb and it flew ok but not great and the motors AND batt were hot to touch....very little margin for error and forget any aerobatics
THEN, I pulled the brushed powertrain in favor of two small Emax red 1200kv motors, same 1200mh 3s battery and Apc 6x4 props and now we're pulling less than 160W but the plane is easier to fly in that it has more power avail to climb and is now coming down with it's battery cooler...since I'm not "leaning" on the throttle so much.
This particular example is why I don't bother with watts per LB......just my view
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Old 05-01-2014, 11:15 PM   #13
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Originally Posted by Wrench66 View Post
Watts per LB can be misleading.....I have not bothered with worrying about it since some variables aren't addressed in the equation. I fly mainly scratchbuilt planes and use a combination of weight, amps, speed and thrust to come to a suitable powertrain combo.
For instance....I built a GWS C47 once that had the std brushed motors and small 5in props, using a small 3s 1200mh battery (for correct balance) my Wattmeter showed 260 watts being pulled at WOT. The plane was approx 1.5lb and it flew ok but not great and the motors AND batt were hot to touch....very little margin for error and forget any aerobatics
THEN, I pulled the brushed powertrain in favor of two small Emax red 1200kv motors, same 1200mh 3s battery and Apc 6x4 props and now we're pulling less than 160W but the plane is easier to fly in that it has more power avail to climb and is now coming down with it's battery cooler...since I'm not "leaning" on the throttle so much.
This particular example is why I don't bother with watts per LB......just my view
--Ray
IMHO, only one problem with that diagnosis. It's apples and oranges, or brushed motors vs brushless motors.

Having rewound brush type motors back in the mid 1980's for more power, I've got a little bit of experience with this. There is a good reason that those brush type motors have been replaced with the brushless versions. The big difference is efficiency of the motors.

The efficiency of some of those brush type motors was simply terrible, perhaps 50% or even worse. The newer brushless motors, at least in sizes over 500 watts or so are running in the high 80% or even 90% efficiency.

As you indicate, a lot depends on the type of model being flown. Whether it is a sailplane, Piper Cub, acrobatic model, or electric jet.

I had a giant 1/4 scale Piper Cub in the late 1990's that was powered by a brush type Astroflight geared 90 motor. Power was 38 Sub C Nicad cells, running about 1100 Watts. That model weighed some 16 pounds. It flew OK, but doing a loop with it was not possible, and rolling it was really risky.

I've also got a 65 inch wingspan acrobatic model that has evolved from a geared Astroflight 40 motor, to a Hacker A50-12S motor. The Astro motor turned a 13X10 prop at 6800 RPM, pulling 700 watts out of the battery, and putting 390 watts on the prop shaft. The Hacker turns a 15X10 prop at 7700 RPM, pulling 1100 watts out of the battery, and putting 960 watts on the prop shaft. Propping the Hacker with the 13X10 prop, we get 8300 RPM, 810 Watts out of the battery, 730 Watts on the prop shaft.

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Old 05-01-2014, 11:24 PM   #14
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Denny you're correct, the brushed vs. brushless propulsion is the determining factor by far in this example......but what of EDF and such? Apples to oranges BUT same watt readings don't give the whole picture since their thrust/power/amp draw doesn't give a clear picture of how inefficient those little hair-dryers are...haha.
Watts per lb is just a partial answer, but it has been pulled up to "this is what you must have for good flight" status with less regard for the other variables that are equally as vital.
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Old 05-01-2014, 11:36 PM   #15
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Originally Posted by Wrench66 View Post
Denny you're correct, the brushed vs. brushless propulsion is the determining factor by far in this example......but what of EDF and such? Apples to oranges BUT same watt readings don't give the whole picture since their thrust/power/amp draw doesn't give a clear picture of how inefficient those little hair-dryers are...haha.
Watts per lb is just a partial answer, but it has been pulled up to "this is what you must have for good flight" status with less regard for the other variables that are equally as vital.
--Ray
Yeah, those EDF power systems are really lousy in efficiency. I've measured 75 Amp currents on some of those three cell foamies in my club. Of course, they are hitting 100 MPH or so.

As you indicate, watts per pound is only a guide line. Nothing more. What might be a "Barely able to get off the ground" amount of power for one person might be exactly what another person wants in his models performance.

I did some work for a club member last year, in the possibility of electrifying a F7F model. The power system would be two Hacker A60-16M motors, running about 2800 watts each. That came out to about 160 Watts per pound. This was a 35 pound model, with only 950 square inches of wing. The wing loading was some 80 ounces per square foot. I told the guy, DON'T DO IT!

One thing that helps in this stuff is one of those computer programs for electric model airplanes. The one I use is www.motocalc.com, free for 30 days, then $39. To me, worth every penny. It's only as accurate as the motor specifications provided by the motor mfg, and some of those specs are not worth the paper they're written on.

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Old 05-01-2014, 11:54 PM   #16
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That Tiger Cat is a great example...wow!
As a primary quick & dirty calc I use Dive Calc http://www.drivecalc.de/ ......it has served me well and is free As you mentioned, the figures listed in the calc's can be a little off (sometimes a lot! haha) so doing you own testing to match up with what the calc says (moto or drive) is the BEST way
Thanks for the discussion.
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Old 05-02-2014, 12:17 AM   #17
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In that changeover from brushed vs brushless the real determining factor was the propeller... you can spin a 5X5 inch prop WOT and just be attempting to "beat the air into submission" getting nowhere... switch to a 6X4 and suddenly have more STATIC THRUST at lower power demand and actually be able to fly.

The correct prop can make a huge difference.

Brushless motors are only marginally more efficient than brushed. And the weight difference is usually not significant to aircraft performance.

Try turning the same prop the same RPM with a brushed vs a brushless (with appropriately comparable motors) and you'll be pulling within 5% of the same watts.
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Old 05-02-2014, 01:55 AM   #18
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THIS is exactly what I am getting at:
Try turning the same prop the same RPM with a brushed vs a brushless (with appropriately comparable motors) and you'll be pulling within 5% of the same watts.


WAtts.......now, add in the other variables and see the HUGE difference......

In the example I was using the GWS 300 can motor which is approx 2300kv, and doesn't like anything much beyond 8-10amps. Using the 3s battery (which fit and CG'd the plane nicely) puts the motor in a corner of using nothing bigger than a short pitch 5in prop....I DID try it with a 2s and slightly bigger 6in dia prop but power was even worse and flight was not fun.
Then I did try it with a pair of Suppo 2212/6 2200kv motors and with nearly the same watts as the 300's we suddenly have sooooo much more speed and absolute 1 to 1+ thrust.
Nearly same watts with same prop, but they're being used much more efficiently.....
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Old 05-02-2014, 02:54 AM   #19
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Originally Posted by fhhuber View Post
In that changeover from brushed vs brushless the real determining factor was the propeller... you can spin a 5X5 inch prop WOT and just be attempting to "beat the air into submission" getting nowhere... switch to a 6X4 and suddenly have more STATIC THRUST at lower power demand and actually be able to fly.

The correct prop can make a huge difference.

Brushless motors are only marginally more efficient than brushed. And the weight difference is usually not significant to aircraft performance.

Try turning the same prop the same RPM with a brushed vs a brushless (with appropriately comparable motors) and you'll be pulling within 5% of the same watts.
Agreed, the proper propeller selection on any electric model airplane can make a huge difference.

As for relative efficiency between brush type and brushless type motors, I did a lot of flying with a hand full of Astroflight Cobalt $$$$ brush type motors. Case in point is the Astro Geared 40 Cobalt motor. (I had three of them) After a flight, that Astro motor was so hot, you could not hold your fingers on it for more than a second or so. I actually put together a blower to cool things off after each flight.

In the same exact model, the Astro motor was replaced with a Hacker A50-12S motor. That Hacker motor is similar size to the Astro motor, but puts out nearly double the watts on the propeller shaft, as compared to the Astro motor.

After landing the model the Hacker is only a few degrees warmer than ambient temperature.

FYI, the Astro motor was pulling a 13X10 prop, the Hacker motor is running a 15X10 prop, at higher RPM.

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Old 05-02-2014, 03:23 AM   #20
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And again you are trying to compare motors where the brushed is rated for HALF the watts of the brushless...

Of course the brushed won't compare well.
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Old 05-02-2014, 04:15 AM   #21
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Originally Posted by fhhuber View Post
And again you are trying to compare motors where the brushed is rated for HALF the watts of the brushless...

Of course the brushed won't compare well.
I've owned Astroflight geared 05, geared 15, geared 25, geared 40, geared 90 brush type motors, Astro geared 40 brushless motors, Astro belt driven 15 motors, plus a hand full of other run of the mill el-cheapo brush type motors. Every one of them were flown in model airplanes. Still got a few of them left. Those Astro motors are expensive, when including the gear box, they are several times more $$$$ than an equivalent Hacker, and far more expensive than some of those decent budget motors.

I presently have Hacker A30, A40-12X, A40-10L, two of the A50-12S, A50-16S, A60-5S and A60-16M motors. These also are presently installed in model airplanes.

Every one of the Astro motors ran so hot you could not hold your finger on them. I actually machined aluminum fins to fit over an Astro 05 motor's case to reduce its temperature. Even running an Astro 40 motor with no prop for two minutes, it would be quite hot. If you ever tried to run one of those Astro motors in reverse, without re-timing the brushes, you can damage it. The current will be considerably higher with the same load.

The Hacker A40-10L motor is similar in its watts rating to the Astro 40 Geared motor. There is no comparison as to performance.

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Old 05-02-2014, 04:25 AM   #22
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Then there must be something wrong with the Astro motors (or you were overloading them)...

When I compared CHEAP speed 500 can motors to similar kV and watt rated brushless motors using the same prop I got virtually the same watt reading when turning the same prop the same rpm.

Any comparison where you are not turning the same prop the same rpm isn't valid. You will be comparing something that isn't going to have any possibility of giving the same performance in flight.

The weight difference was an average of 20% lighter for the brushless motor. But in many cases replacing the brushed with brushless we move to a higher watt rated motor to bring the weight back up for CG. Its common to need the nose weight when making the change from brushed to brushless.
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Old 05-02-2014, 04:31 AM   #23
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Originally Posted by fhhuber View Post
Then there must be something wrong with the Astro motors (or you were overloading them)...

When I compared CHEAP speed 500 can motors to similar kV and watt rated brushless motors using the same prop I got virtually the same watt reading when turning the same prop the same rpm.

Any comparison where you are not turning the same prop the same rpm isn't valid. You will be comparing something that isn't going to have any possibility of giving the same performance in flight.

The weight difference was an average of 20% lighter for the brushless motor. But in many cases replacing the brushed with brushless we move to a higher watt rated motor to bring the weight back up for CG. Its common to need the nose weight when making the change from brushed to brushless.
Nope, I was running those motors well within their ratings. I even talked personally with the Astro motor designer at a big electric fun fly in Allentown PA in the late 1990's. We discussed how to set up the motor timing to optimum. The best timing of these motors will vary depending on the load on the motor.

That might be true of the smaller can type motors, vs the real small brushless motors. Those little brushless motors under perhaps 300 watts only run about 80% efficiency. There are also some brushless motors that are not made very well, and have lousy efficiency. Some of the Rimfire motors are an example. Some of those brushless motors the same size as the Hacker A50 series motors have winding resistance 4 or 5 times that of the Hackers. Cheap motors don't perform well, whether brush type, or brushless type.

But believe me, when you get to 1000 to 2000 watt high quality motors or larger, there is a significant difference in performance between brush and brushless type motors.

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Old 05-02-2014, 04:46 AM   #24
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I have the big motors too...

Same prop... same RPM very small difference in watts when turned by motors of similar ratings.
It works any time you aren't overloading the motor and turning it into a space heater.
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Old 05-02-2014, 06:10 AM   #25
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Originally Posted by fhhuber View Post
I have the big motors too...

Same prop... same RPM very small difference in watts when turned by motors of similar ratings.
It works any time you aren't overloading the motor and turning it into a space heater.
Here are some numbers from www.motocalc.com. Motocalc is pretty close to the real numbers I had when running those Astro motors. Note that the Astro motor needs a 10S LiPo, vs the Hacker's 5S LiPo. The Astro is rated up to a 10S LiPo battery. The Astro motor weighs more than double the Hacker motor. Both are rated at about 1100 Watts.

Note that an Astro 60 motor is required to match the power capability of a Hacker A40-10L. And, motocalc indicates that the Astro motor is going to run over 260 degrees F.

If you run both motors at about 400 watts, you are right, they will both be pulling about the same number of watts. If you run the Astro at its rated 35 Amps and 1100 watts, motocalc suggests the motor will hit 400 degrees F.


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