Electric engines
The question about the engine system comes right after the decision of the model, so you have to make a decision quite early. Today it only makes sense to build in brushless electric engines, brushed ones would have a not so good efficiency, not so much power and are just too old.
Basics:
The easiest noticeable difference between a brushed and brushless engine is, that the brushless one has three cables. On that, you can recognize them immediately. Why it is like that how does a brushless engine works in detail is explained on several pages over the internet. Also a noticable difference is, that brushless engines are most time outrunners, this means that the shell is rotating. There you need to take care that this will not damage any cables.
Choose the engine:
To choose the right engine seems to some new guys in this hobby often very difficult. But there is a small guide that can help:
If you have a new model, you should know how much the take off weight will be. The power of an electric engine will always be stated as Watt or kW (Kilo Watt, 1kW=1000W). According to the weight / performance ratio (W/kg) we can estimate the needed power:
100W/kg= The model can stay in the air. (Only as "rescue system" when you're going slope soaring)
150W/kg= Launching by hand and slow climb. (Beginner electric sailplane)
200W/kg= Take off from the ground and good climbing. (Trainer)
250W/kg= Very good climbing. (Warbirds, calssic pattern flying)
300W/kg and more: Straight up and accelerating. (3D Models, Hotliner, Pylon, Speeder)
Calculation example: Warbrid with about 4kg take off weight -> 4kg*250W/kg=1000W=1kW, an engine with about 1kW should be selected.
Please consider that this are only estimated values which can be very different in real life because of many factors.
As next, we get to the kV rating. most people interpret this as power, but this is mostly false. kV means nothing else, then rotations per voltage. If we would have an engine with 3000kV on a 3S LiPo, this would mean that it has a maximum of about 33300 rotations per minute (3*3,7*3000).
According to the purpose we must consider the kV. If we have a model with high speeds, then we would normaly use a small prop which should rotate very fast. So we will select an engine with high kV. If we have a plane which is flying slower or needs a lot of static thrust, we will select an engine with less kV and a bigger prop.
You only have to take care that you won't overload the engine. Mostly there are recommendations from the manufacturer which prop he would suggest. Also you can try www.ecalc.ch, which is a very good adress for calculating the power chain.
If you have a new model, you should know how much the take off weight will be. The power of an electric engine will always be stated as Watt or kW (Kilo Watt, 1kW=1000W). According to the weight / performance ratio (W/kg) we can estimate the needed power:
100W/kg= The model can stay in the air. (Only as "rescue system" when you're going slope soaring)
150W/kg= Launching by hand and slow climb. (Beginner electric sailplane)
200W/kg= Take off from the ground and good climbing. (Trainer)
250W/kg= Very good climbing. (Warbirds, calssic pattern flying)
300W/kg and more: Straight up and accelerating. (3D Models, Hotliner, Pylon, Speeder)
Calculation example: Warbrid with about 4kg take off weight -> 4kg*250W/kg=1000W=1kW, an engine with about 1kW should be selected.
Please consider that this are only estimated values which can be very different in real life because of many factors.
As next, we get to the kV rating. most people interpret this as power, but this is mostly false. kV means nothing else, then rotations per voltage. If we would have an engine with 3000kV on a 3S LiPo, this would mean that it has a maximum of about 33300 rotations per minute (3*3,7*3000).
According to the purpose we must consider the kV. If we have a model with high speeds, then we would normaly use a small prop which should rotate very fast. So we will select an engine with high kV. If we have a plane which is flying slower or needs a lot of static thrust, we will select an engine with less kV and a bigger prop.
You only have to take care that you won't overload the engine. Mostly there are recommendations from the manufacturer which prop he would suggest. Also you can try www.ecalc.ch, which is a very good adress for calculating the power chain.
Engines used by me:Name: D2836-1700
Manufacturer: Mystery Sold by: Miscellaneous Meassurements: Ø28x36mm kV:1700 Max. Amp: 28A Max. Current: 3S Max. Power: 300W Weight: 73gr. Price: 15€ Used in: X-Free An engine which looks very good at first sight and also after first flights. Unfortunately, after about 50 flights, the problem occours that the shaft is amde of very cheap material and starts to bend. This leads to a big unbalance and it is not useable anymore. I will not use it again.
Name: NTM Prop Drive 28-36 3000KV
Manufacturer: Hobbyking Sold by: Hobbyking Meassurements: Ø28x36mm kV: 3000 Max. Amp: 55A Max. Current: 4S Max. Power: 755W Weight: 87gr. Price: 15€ Used in: Radjet |
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Unbelieveable what this small engine can take in the Radjet. Even with 60A on 4S (890W) he can take full throttle for one and a half minute. The heat development is then of course an important factor, but he is used behind the manufacturer design data. The the 3S pack is used in the Radjet, the 400W let him, of course, being "cool".
Clearly recommendation!
Clearly recommendation!
Name: 3W
Manufacturer: HET
Sold by: Miscellaneous
Meassurements: Ø28x37mm
kV: 2980
Max. Amp: 30A
Max. Current: 4S
Max. Power: 450W
Weight: 78gr.
Price: 50€
Used in: Voodoo
Manufacturer: HET
Sold by: Miscellaneous
Meassurements: Ø28x37mm
kV: 2980
Max. Amp: 30A
Max. Current: 4S
Max. Power: 450W
Weight: 78gr.
Price: 50€
Used in: Voodoo
I've searched over weeks an alternative for the Voodoo, but there is no engine for that purpose which is as good as the HET 3W. It's an inrunner where the cables are on the back but he still has 6 poles, because of that, the engine brake from the ESC ist working and the prop will stop in the air when you reduce the throttle to 0%. Also the efficiency is very good, with a 4,75² on 3S he only pulls 28A where the NTM Prop Drive 28-36 3000kV already needs 36A. But it is still interessting that he has a very high heat development, so take care that he gets cooled well. Clearly recommendation!
Name: Turnigy SK3 3542 1000kV
Manufacturer: Turnigy
Sold by: Hobbyking
Meassurements: Ø35x42mm
kV: 1000
Max. Amp: 45A
Max. Current: 4S
Max. Power: 670W
Weight: 14
Price: 35€
Used in: -
Manufacturer: Turnigy
Sold by: Hobbyking
Meassurements: Ø35x42mm
kV: 1000
Max. Amp: 45A
Max. Current: 4S
Max. Power: 670W
Weight: 14
Price: 35€
Used in: -
I bought this engine for a colelague who needs it for his CHK Thermikstar. The quality is SK3 like very good. There is nothing negative to say about the finish and it will be delivered in a small box with plenty of accessories. You can choose if you want to bolt it in the classic way behind the firewall or to turn it 180° and mount it in front of the firewall. The cables are very smooth and seems to be a little small, but for 45A on 4S it should be enough.
Name: NTM Prop Drive 42-48 650kV
Manufacturer: Hobbyking
Sold by: Hobbyking
Meassurements: Ø42x48mm
kV: 650
Max. Amp: 70A
Max. Current: 5S
Max. Power: 1,3kW
Weight: 243gr.
Price: 30€
Used in: Votec 322
Manufacturer: Hobbyking
Sold by: Hobbyking
Meassurements: Ø42x48mm
kV: 650
Max. Amp: 70A
Max. Current: 5S
Max. Power: 1,3kW
Weight: 243gr.
Price: 30€
Used in: Votec 322
The Votec is with that engine nearly overpowered. Same like in the Radjet, there is nearly no heat development and the engine is running flawless since day one. I can recommend this engine without doubts!
Name: SK3 Competition Series 4249-1600kv
Manufacturer: Turnigy
Sold by: Hobbyking
Meassurements: Ø42x49mm
kV: 1600
Max. Amp: 75A
Max. Current: 6S
Max. Power: 1,66kW
Weight: 219gr.
Price: 30€
Used in: T-Rex 500 ESP
Manufacturer: Turnigy
Sold by: Hobbyking
Meassurements: Ø42x49mm
kV: 1600
Max. Amp: 75A
Max. Current: 6S
Max. Power: 1,66kW
Weight: 219gr.
Price: 30€
Used in: T-Rex 500 ESP
Maybe the engine with the best price / performance ratio for a 500 helicopter. With the logging data from the ICE 75 i can see that the engine is delivering exactley the 1,6kW as it should. Only after about 50 flights, the connection between the stator and the shaft became loose which leaded to some clacking sounds when he spinned up. After repairing that with some CA, he runs flawless and also has nearly no heat development, even on very hot days. Definitely a secret hint for all who are not 100% sure which engine to put in their 500.
Name: NTM Prop Drive 42-58 500kV
Manufacturer: Hobbyking
Sold by: Hobbyking
Meassurements: Ø42x58mm
kV: 500
Max. Amp: 60A
Max. Current: 7S
Max. Power: 1,3kW
Weight: 319gr.
Price: 38€
Used in: Piper L4
Manufacturer: Hobbyking
Sold by: Hobbyking
Meassurements: Ø42x58mm
kV: 500
Max. Amp: 60A
Max. Current: 7S
Max. Power: 1,3kW
Weight: 319gr.
Price: 38€
Used in: Piper L4
My Workhorse. After uncountable flights, this engine is doing serious work at towing various gliders. The engine is running flawless and the meassured data is exactley as the manufacturer promised. Unobtrusively, powerful, reliable, what should you want more?