• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Solved Prop for 3660 1950kv inrunner (80mm ESC motor)

Ryan O.

Out of Foam Board!
#1
I got this motor meant for RC cars but similar in spec to those on 80mm 6s edfs for a speed plane and have no idea what size and pitch prop to use on it.
https://www.amazon.com/dp/B09WK1HCH2/?tag=lstir-20
I couldn’t find any prop-kv charts for inrunners and there are no manufacturer recommendations for this or similar motors and I wasn’t able to get prop calc to work. My guess is anywhere from a 6x9 to a 9x9 apc, but I don’t want to spend a bunch on different props, so just a ballpark is helpful.
 

Fidget

Active member
#2
I also couldn't find something similar in an existing plane, which is my usual trick. Based on this 1950kv motor, I think I would start with 5x5 3-bladed prop. I would try that and measure amps with a multimeter. If that's not pushing the amps too high, try a 4 blade or go up to 6 inch. Clamp it down well as you test; it will also be a vicious finger cutting machine.
 

Ryan O.

Out of Foam Board!
#3
I also couldn't find something similar in an existing plane, which is my usual trick. Based on this 1950kv motor, I think I would start with 5x5 3-bladed prop. I would try that and measure amps with a multimeter. If that's not pushing the amps too high, try a 4 blade or go up to 6 inch. Clamp it down well as you test; it will also be a vicious finger cutting machine.
I’ll try a 6” 2 blade then since 3 blades isn’t great for speed and it’s close enough resistance wise.
 
Last edited:

Ryan O.

Out of Foam Board!
#5
Old motor out, new motor in. I’ll update when I do prop tests. I ordered a bunch of apc props: 6x4.5, 6x5, 6x6, 6x7, 7x5, and 7x6 if I remember correctly.
image.jpg
image.jpg
image.jpg
image.jpg
 

FAI-F1D

Free Flight Indoorist
#6
Try a 7x6 APC to get started. If it stays reasonably safe on temperature, you can explore higher pitch, but stay at 7" diameter. If it gets hot, drop down to a 6.5x6.5 APC. Bear in mind these are glow props so you'll need a reamer to open up the hub for your spinner. I recommend Graupner spinners if you can find them.

A few other notes: don't move away from APC glow props. They're efficient and able to withstand the extremely high rpms these motors produce. On 6s with a 6.5x6.5 you're going to be dancing around 25k rpm. Don't skimp on escs or connectors. These things can suck a ton of current, easy to punch through 200A so a good esc and careful throttle management are critical. This is where a safety note comes into play: DO NOT power your electronics off the motor power battery. Disconnect the red wire going from your esc to the receiver and get a small BEC that will allow you to power the receiver off a 2s lipo around 500mah. Failure to do this isn't merely risky, it's negligent. These things blow up ESCs on occasion and then you've got an uncontrollable missile going who knows where. The BEC gives you control to get it down. That said, at the first sight of smoke, land NOW before the fire shorts your signal lead to the esc and kills the BEC battery. Don't ask how I know that...
 

Ryan O.

Out of Foam Board!
#7
Try a 7x6 APC to get started. If it stays reasonably safe on temperature, you can explore higher pitch, but stay at 7" diameter. If it gets hot, drop down to a 6.5x6.5 APC. Bear in mind these are glow props so you'll need a reamer to open up the hub for your spinner. I recommend Graupner spinners if you can find them.

A few other notes: don't move away from APC glow props. They're efficient and able to withstand the extremely high rpms these motors produce. On 6s with a 6.5x6.5 you're going to be dancing around 25k rpm. Don't skimp on escs or connectors. These things can suck a ton of current, easy to punch through 200A so a good esc and careful throttle management are critical. This is where a safety note comes into play: DO NOT power your electronics off the motor power battery. Disconnect the red wire going from your esc to the receiver and get a small BEC that will allow you to power the receiver off a 2s lipo around 500mah. Failure to do this isn't merely risky, it's negligent. These things blow up ESCs on occasion and then you've got an uncontrollable missile going who knows where. The BEC gives you control to get it down. That said, at the first sight of smoke, land NOW before the fire shorts your signal lead to the esc and kills the BEC battery. Don't ask how I know that...
I’ve got a 800mah LiFe pack for receiver power that I managed to jam in there already. My main concern is ESC cooling since the ESC is behind the 2 1000mah 6s batteries, the leads were pretty long and I needed the nose weight. The picture is from before I added the receiver pack since it was just one less wire to deal with during servo setup.
3729645D-8A89-4324-B8F7-5DAD03B74FDD.jpeg

I’ve got a great planes aluminum spinner, but if it ends up being too heavy or too flimsy I’ll swap it out for a graupner like you recommended. I’ve done short a static test running a 6x6 prop and everything was room temperature, so after the first flight on the 6” I can likely move up to a 7” if cooling ends up being alright.
There’s already another club member with an electrostreak that goes 150 with a big outrunner and a 9” prop, and I’ve made the necessary structural modifications (reinforced v-stab, dual aileron servos, and cutting the ailerons short to prevent flutter at the tip from wingtip vortexes).
 

Ryan O.

Out of Foam Board!
#8
Try a 7x6 APC to get started. If it stays reasonably safe on temperature, you can explore higher pitch, but stay at 7" diameter. If it gets hot, drop down to a 6.5x6.5 APC. Bear in mind these are glow props so you'll need a reamer to open up the hub for your spinner. I recommend Graupner spinners if you can find them.

A few other notes: don't move away from APC glow props. They're efficient and able to withstand the extremely high rpms these motors produce. On 6s with a 6.5x6.5 you're going to be dancing around 25k rpm. Don't skimp on escs or connectors. These things can suck a ton of current, easy to punch through 200A so a good esc and careful throttle management are critical. This is where a safety note comes into play: DO NOT power your electronics off the motor power battery. Disconnect the red wire going from your esc to the receiver and get a small BEC that will allow you to power the receiver off a 2s lipo around 500mah. Failure to do this isn't merely risky, it's negligent. These things blow up ESCs on occasion and then you've got an uncontrollable missile going who knows where. The BEC gives you control to get it down. That said, at the first sight of smoke, land NOW before the fire shorts your signal lead to the esc and kills the BEC battery. Don't ask how I know that...
Own other thing, would you recommend using a set screw or collet prop adapter?
 

Ryan O.

Out of Foam Board!
#9
First, about the original topic of the thread, I decided to do the maiden on a 7x5 prop instead of a 6x6. After the short flight I definitely think I can go up to a 7x6 or even a 7x7.
8E4A1CFE-3A09-4AC8-8CA1-EB2266D076CC.jpeg

The plane flew great, cruising at around 1/8 throttle. I had already done a brief half throttle pass at about 95 and early into the following 2/3 throttle pass the vertical stabilizer failed at about 105 mph. I had already done minor reinforcements but it obviously wasn’t enough. The new tail will likely be solid balsa with pins going through the fuselage.
3BEB07F7-60C2-4CD9-AF71-B1F43C2886CC.jpeg
853790A6-9BAE-44F9-8773-70EEB597A74B.jpeg
2DA547A3-FBC2-4732-B415-9A8623738424.jpeg
The v-stab actually stayed attached to the plane by the pull-pull system linkages and the electrostreak just wobbled around the sky until it hit a tree. I tried to turn away but it wasn’t able to maneuver at all. The plane’s not really that damaged at the moment, the electronics even worked. Only visible damage, besides the vertical stabilizer, is a chip in the wingtip.
ECB8F96F-5510-4A6F-801D-67536F5DB507.jpeg

Google drive links to video, they may or may not work.
https://drive.google.com/file/d/1jxkjioZAx6zwh0Y_vfKJAnGtq4_GYUn6/view
https://drive.google.com/file/d/14q-Qudh1GycI7-7QLZygKUqgGc-NE-Ur/view
 

JetCrafts

Active member
#10
First, about the original topic of the thread, I decided to do the maiden on a 7x5 prop instead of a 6x6. After the short flight I definitely think I can go up to a 7x6 or even a 7x7.
View attachment 230519
The plane flew great, cruising at around 1/8 throttle. I had already done a brief half throttle pass at about 95 and early into the following 2/3 throttle pass the vertical stabilizer failed at about 105 mph. I had already done minor reinforcements but it obviously wasn’t enough. The new tail will likely be solid balsa with pins going through the fuselage. View attachment 230511 View attachment 230512 View attachment 230513 The v-stab actually stayed attached to the plane by the pull-pull system linkages and the electrostreak just wobbled around the sky until it hit a tree. I tried to turn away but it wasn’t able to maneuver at all. The plane’s not really that damaged at the moment, the electronics even worked. Only visible damage, besides the vertical stabilizer, is a chip in the wingtip.
View attachment 230514
Google drive links to video, they may or may not work.
https://drive.google.com/file/d/1jxkjioZAx6zwh0Y_vfKJAnGtq4_GYUn6/view
https://drive.google.com/file/d/14q-Qudh1GycI7-7QLZygKUqgGc-NE-Ur/view
potato cannon , potato cannon in true ft fashion
 

FAI-F1D

Free Flight Indoorist
#11
Electrostreak? Dang, what a classic! Definitely gonna need some reinforcing...you're *slightly* outside the design operating range. ;)

I'm not a big fan of set screws. They work their way loose at the worst possible time. I figure if a collet can handle 12kW on the GM F5B folders, it's clearly the way to go.

ESC should always be forward of the batteries, for at least 3 reasons:

1. Shorter wires between motor and esc means less inductive interference, less resistance heat, and better efficiency.
2. Better cooling. Make sure you have a good cooling inlet or two and a good sized exhaust outlet aft of the batteries. Batteries are disposable. If they overheat, get new ones. HRB, Pulse, and GNB all seem able to handle extreme heat repeatedly without dying. There are others as well but those are my favorites so far.
3. Keeps the explodey component away from the control center.
 

Ryan O.

Out of Foam Board!
#12
Electrostreak? Dang, what a classic! Definitely gonna need some reinforcing...you're *slightly* outside the design operating range. ;)

I'm not a big fan of set screws. They work their way loose at the worst possible time. I figure if a collet can handle 12kW on the GM F5B folders, it's clearly the way to go.

ESC should always be forward of the batteries, for at least 3 reasons:

1. Shorter wires between motor and esc means less inductive interference, less resistance heat, and better efficiency.
2. Better cooling. Make sure you have a good cooling inlet or two and a good sized exhaust outlet aft of the batteries. Batteries are disposable. If they overheat, get new ones. HRB, Pulse, and GNB all seem able to handle extreme heat repeatedly without dying. There are others as well but those are my favorites so far.
3. Keeps the explodey component away from the control center.
For going only twice the designed speed it handled it pretty well. I copied the modifications from another guy at the field with a 150mph electrostreak, mostly around the wing ailerons. Seeing as it didn’t disintegrate from the g forces when the tail detached I’d guess the rest of the airframe is strong enough. The wing fell out of the tree already, according to another club member who picked it off the ground it was perfectly fine besides a chip in the wingtip.
 

Ryan O.

Out of Foam Board!
#13
I picked up the wing and it looks decent, probably a third a days’ work to repair the cosmetic damage. The fuselage did shift a little in the tree, so hopefully it falls soon.
image.jpg
image.jpg
image.jpg
image.jpg