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Help! Ultra micro warbird build

#1
Hello everyone, I could use some help with an ultra micro that I'm currently building.

I have a 21.5" EPO foam warbird, that I have all the details worked out, with the exception of the receiver and esc.
Like all ultra micro models, very lite weight to power ratio is key. So in order to keep the weight down, I'm using all eflite UMX electronics. Due to the scale size and weight of the model, the propeller is a 6 x 4 on a TomCat 1806-3100kv brushless motor. ( I cannot use a eflite BL180 series motor (2500-3600kv) since those series motors are rated for smaller and less aggressive props)

I would like to use an eflite EFLA6420BL DSMX 6 channel ultra micro receiver, with an integrated ESC and both tail section servo's. The issue is the current draw of the brushless motor, which is 6.4amps max. (full rpm with full battery charge) is too high for the receiver. ( I think )
I cannot verify the max current cut-off setting of this particular eflite receiver/esc, but from what I have found most other eflite ultra micro receivers are set at 5.0-5.2 over current protection cutoff.
I have also looked for a different brands or style receiver and esc set up, but due to either incompatible design, excessive weight and/or size, I have not found anything that will work.
Any working suggestions would be greatly appreciated. Thank You.

Here are some more specs on my model;
Model: 21.5" wingspan UMX P40 warbird.
Material: EPO foam.
Battery: Turnigy Nano-Tech 300mah 2s 45c lipo.
Motor: TomCat 1806-3100kv brushless motor.
Aileron servo's: eflite A2030 Linear servo
Total flying weight: 155-165 grams.
 

quorneng

Well-known member
#2
I do wonder if you are not over powering your warbird a bit.
6.4 A from a 2s is virtually 50 W of power.
In a plane weighing 165 g that gives a power loading of 138 W/lb. That is entering 'unlimited vertical territory' which is fine but at 21.5" span you are likely to have significant torque issues, particularly with no ailerons, in a low wing plane if power is applied at low speed.
You really are faced with a choice.
Use a different prop to keep the Amps within the integrated receiver limit or keep that motor/prop and rethink using the integrated receiver.
 
#4
I do wonder if you are not over powering your warbird a bit.
6.4 A from a 2s is virtually 50 W of power.
In a plane weighing 165 g that gives a power loading of 138 W/lb. That is entering 'unlimited vertical territory' which is fine but at 21.5" span you are likely to have significant torque issues, particularly with no ailerons, in a low wing plane if power is applied at low speed.
You really are faced with a choice.
Use a different prop to keep the Amps within the integrated receiver limit or keep that motor/prop and rethink using the integrated receiver.
Hello quorneng, Thanks for your input. As with most warbirds, they require a very high power to weight ratio. General rule is 100-150 watts per pound. I also did a thrust test on another UMX warbird that I own, an eflite UMX P47. The P47 is stock except for the motor, which I upgraded it from the stock BL180-2500kv to the BL180-3000kv motor. The P47 also uses a 4.5 x 3 size prop and yet still has close to 150 watts p/lb of thrust because it is so lite. Total weight of the UMX P47 is 3.35 ounces.

The UMX P40 model I'm currently building is twice as heavy (6-7 ounces) and the thrust test I did using a FMS 12 amp esc was showing around 85-90 watts per/lb of thrust. So I really do not want to go with a smaller prop. Plus, the P40 wings have less lift and more wing loading than the UMX P47, so I would prefer to have the thrust closer to the 150 watt p/lb mark. Oh yes, the P40 I'm building has ailerons.
 
#5
I would put a much smaller motor in there, an 1106 or similar, an 1806 is massive in something that light.
Hello FDS, The original manufacture of the airframe calls for a 1820 size brushless motor. That was most likely because of the needed power to drive the 6 x 4 prop. I could not find a 1820 motor that was not too heavy and had a high enough KV rating to work on this model. The 1806-3100kv motor was the best I could find for power and weight. Based on my research, counculations and testing a 1106 motor would not have the capability to drive a prop that is required to obtain the amount of needed thrust.
 
#6
I do wonder if you are not over powering your warbird a bit.
6.4 A from a 2s is virtually 50 W of power.
In a plane weighing 165 g that gives a power loading of 138 W/lb. That is entering 'unlimited vertical territory' which is fine but at 21.5" span you are likely to have significant torque issues, particularly with no ailerons, in a low wing plane if power is applied at low speed.
You really are faced with a choice.
Use a different prop to keep the Amps within the integrated receiver limit or keep that motor/prop and rethink using the integrated receiver.
quorning, One other note about watts per pound. Watts is just a form of power consumption, which is a direct result of load on the motor. What watts per pound does not show is how much thrust the motor and prop are creating at a given voltage. That is why I use a thrust comparison test to my working UMX P47. The eflite UMX P47 has incredible flight performance because of the very good thrust to weight ratio and gives me a great reference point to use for building other UMX models of similar size and design.

So my test are for actual thrust created by the motor and prop, not motor power consumption.
Thanks for your input.
 

MiniacRC

Well-known member
#7
Sounds like a fun project! :)

An 1806 3100 on 2S swinging a 6" prop seems like alot of potential torque roll for such a light and small bird. I've flown some scratchbuilt 21" span warbirds on an 1806 2300 kv motor swinging a King Kong 6*4 propeller (2S and 3S) but they were probably closer to 200 grams flying weight. The biggest reason they flew successfully, is proper thrust angle.

For such high rpm operation with a 6" prop on a small plane, I'd recommend providing lots of right thrust angle on the motor. Here's one of mine, a flitetest style Bloody Mini P40 Warhark on the aforementioned setup. It has probably close to 4˚of rightward thrust and 1˚ of down thrust to account for inertial and aerodynamic effects, such as P-factor, gyroscoping precession, slipstream induced yaw, etc - factors that will be more significant at our small scale. Hope your project takes to the skies!

 

Hondo76251

Well-known member
#8
I killed one of those recievers in short order the last time I did a build with one, that's what I had in this originally:


Similar size and weight, I've got a 10a esc in it now
 
#9
Awesome video's guys! My UMX P40 is 100% scale, very detailed. I certainly hope my build flies as well as MiniacRC's plane.

I just finished a larger custom built, scale 800mm P40 warbird. I had one that was a great flyer for about two and half years, until I made a stupid mistake and destroyed it in a crash.
Looked for months for another one, but could not find any as the FMS manufactured airframe was out of production over three years ago. My father found one that someone had, but could not get it to fly. So my dad bought it for me. I just completed the build last week. Looks awesome! Looking forward to flying it this summer.
If this one flies as well as my last one, it will be a blast. It has incredible power to weight ratio with incredible aerobatic capability.
What makes this plane fly so well is the improvements from the factory model.
This what I changed:
Removed factory 3015-1700kv brushless motor, 20amp esc, 7 x 6 3 blade prop and a 1000mah 2s lipo battery.
Installed: Detrum 2815-1100kv brushless motor, 30 amp esc, 9 x 6 3 blade Dynam prop and a zippy 500mah 3 cell lipo battery
Open all the scale ports on the nose section, for cooling air intake as well as adding a outlet port in the tail section.
Repainted and decals to a early 1942 Army Air Corp designation and insignia's

DSC02285.JPG Attached is a picture of my completed 800mm P40 custom build.
 

Hondo76251

Well-known member
#11
I like the AR6335 a lot now, used several with great success. As3x make a huge difference in smaller models.

Think that one just has a compact 10a banggood special Simon k now IIRC,
20200404_214742.jpg

but Ive had good luck with these hobbywings:
20200404_214808.jpg

I do a lot of twin engines myself so I like opo esc's w/a separate BEC for the receiver and servos...
 
#13
After more research for the best motor, ESC, receiver and servo combination for this model, I decided to use the eflite UMX system. This will give me the best weight to power ratio. I also spoke with Horizon Hobby Tech support, which really helped me get some much needed answers to several questions and thoughts.
So essentially I will be installing all electronics from an eflite UMX Timber, minus the motor. Since the eflite 180BL series motors cannot handle a 6 x 4 prop and the 180BL motor cannot be correctly installed into this particular model, I will use an 1806-3100kv brushless motor. The AS6420BL DSMX all-in-one receiver/ESC/tail servo board assembly with gyro has a higher maximum motor amperage rating, which can work with my motor.
I have everything needed except for the 6420 receiver, which I hope to have soon. I will keep everyone updated as I progress with the build.
Thanks for everyone and there suggestions.
 
#14
UPDATE: I just completed the build. All the electronics (Servo's and receiver/esc board) are for an eflite UMX P47 Thunderbolt. This also gives me eflite's stbility gyro, which is great for ultra micro's. I was able to perform some additional test with the receiver/esc board and motor, which I found work well together. Max of 5.1amp draw with a Turnigy 2s 300mah 45c battery. Motor stays nice and cool and thrust is decent. All the electronics fit well with very little trimming of the foam. I did have to add wire extensions for the aileron servo's and all of the linkage I custom made myself.
After completion, including paint and decals, the total weight is 160 grams. Not too bad all things considering. I have to wait for good flying weather to see how well it will fly, as we have been in a rainy/windy weather pattern for some time. Based on my experience, I do not feel it will perform as well as my eflite UMX P47 because it does not have as good of a power-to-weight ratio, but it should be a decent flyer. Below is a few photos of the completed model. Thanks for everyone with their suggestions.
 

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#17
Hi Ketchup (love the name),
It's not 100% scratch built. The foam airframe was sold as being manufactured by a company called Flyfly hobby. Flyfly hobby did not actually make it, they sub contract it to someone else, as Flyfly hobby manufactures only high end composite rc jets and gliders. Anyway, the airframe is a kit that comes in several epo foam pieces that needs glued together and includes some premade plastic parts as well.
I came up with the rest on my own, motor, receiver, servo's etc...
I also designed and made a custom motor mount, all control linkages and prop spinner. I hand painted the entire plane, including the canopy (which I wish looked better) and had a decal shop make all the decals for me.
The wing servo covers are from a eflite UMX P47 as well as all of the electronics. The motor is a supposed to be a G-Force brand 1804-3100kv brushless motor, although there are no markings on the motor. The prop is a 6x4 Master Airscrew brand.
I hope the thrust to weight ratio is good enough to do aerobatics. My eflite UMX P47 is a absolute incredible performer with a very wide flight envelope, but it only weighs 95 grams. (flying weight)
This P40 weighs 160 grams, but has a larger prop and slightly higher kv motor. So I really am not sure how well it will fly until I try.

Thanks MiniacRC, I hope it flies well too. The paint scheme is somewhat based off the P40's of the 57th fighter group stationed in North Africa. I'm happy with how well it looks, although I coated the paint with a protective clear coat that was supposed to be a matte finish, not glossy. Hope it flies as good as it looks. I would love to build a BF-109 in the same size, if I could find one.
 
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#18
Hi MiniacRC, As for the possible motor torque issue you mentioned in a previous post, I'm hoping the extra weight and larger wingspan will keep the torque roll down. The 6x4 prop is actually scale to the model and since yhe model is heavier and larger than comparable eflite UMX warbirds, I think it might be fine. I did place the same motor degree down and to the right angles that eflite uses on their UMX warbird models, so I'm hoping this will works for me as well. I will keep everyone posted once I have the inaugural flight.
 

Ketchup

4s mini mustang
#19
I would love to build a BF-109 in the same size, if I could find one.
Maybe try scratch building with foam? Or maybe get some thick insulation foam and carve one out. It shouldn’t be too bad and the plane would look nice with some work. Also thanks, Ketchup is a nickname that my friends call me.
 
#20
UPDATE;
Here is an update.

Today, for the first time this spring, the weather was finally favorable to fly. So I took two (2) of my UMX planes to the field. My favorite plane, the eflite UMX P-47 Thunderbolt and the new custom built UMX P-40 Warhawk.

I flew the P-47 first, just to refresh my self with the control and the feel of the plane and radio. Then I tried the custom built P-40, which unfortunately did not do too well. The first launch flew poorly (very difficult to control) and crashed within 10 seconds, nose first into the ground.

Inspected and tested everything on the plane and surprisingly it handled the crash quite well. Almost no damage, just some slight wrinkling of the fuselage, but nothing broken, loose, bent or shifted. Even the prop and motor were fine. Wow!

So I launched it a second time. This flight was not much better, lasted close to 30 seconds then nosed into the ground hard. The only good thing about the second flight, it gave me enough time to get a feel for what is going on and why this model was flying so poorly. This model is just too under powered, even at full throttle. First, I had a very difficult time keeping it to fly level, as the flight controls seamed extremely sensitive. But as soon as the nose began to point upward, the model stalled and I was constantly trying to recover and gain control.

The second crash did more damage, but again very minor and was repairable with about 5-10 minutes of work. I decided to stop at that point and not attempt another flight.

I was hoping that it would have flown better, but I had some doubts, since the weight was more than I wanted it to be. (165 grams) That is about 70 grams more than the eflite UMX P-47. The motor and prop combination (1804-3100kv motor and a 6x4 prop), was expected to have more thrust then the UMX P-47, but I believe the eflite built-in esc in the receiver, is too restrictive and not providing full battery voltage to the motor.

I say this, because on my original build, I was testing the same motor and prop combination, using a separate FMS 12amp ESC and a AR400 receiver. That same motor and prop combination was pulling 6.1-6.2 amps at full throttle with a fully charged 2s battery pack. With the eflite UMX control board/esc combo that I'm now using, tested only 5.0-5.1 amps at full throttle! Same motor, prop and battery. So I believe my thrust was also lower than what I was expecting, due to lower voltage output to the motor.

During the build, the eflite electronics (receiver/esc and servos) was the lightest configuration I could find. Plus, the motor I'm using is the only 3000+ kv motor I could find that can handle a 6x4 prop and still not overload the eflite esc/receiver board. So I do not believe there is anything I could do to reduce the weight enough to compensate for the lack of thrust.

So for now, its back to the drawing board.

If anyone has any suggestions, please let me know.

Thanks,

Steve K.