3DHS 70" Velox

[Only Fine Helis]

Well, I have a motrolfly on 4325 425kv on the way. Should have listened to begin with

How much different is the mounting pattern?

 

[njswede]

Did you measure the watts? A quick calculation indicates that you would pull north of 2000w on that setup. And over 100A! Ecalc.ch shows a motor temp of 244F!

 

[Only Fine Helis]

I didn't have a temp gun with me at the field, but I wouldn't doubt the 244 degrees.

I had an inline watt meter that I was planning on installing after the basic setup on the maiden. Looks like I definitely got the kart before the horse.

 

[Only Fine Helis]

NJSwede,

I'm curious, what figures do you get when you plug in the 3dhs recommended A50-16S 365kv with an 18x8 or 18x10?

Thanks again!

 

[njswede]

You can check it yourself using Hacker's prop and motor calculator here: http://www.ecalc.ch/motorcalc.php?hacker&lang=en&elevation=300

On a 18x8 prop, you'd get 1468W and on a 18x10, you'd get 1708W. Both values are above the 1250W which is the max rated power.

Also, keep in mind that power doesn't increase linearly when you increase speed and prop size. Increasing the prop diameter actually increases the power required to drive the prop as the increase in diameter to the power of five! Increasing the kV increases the power by the power of two. In other words, if you increase the diameter by 10%, you increase the power by 1.1 * 1.1 * 1.1 * 1.1 * 1.1 = 1.6. Going from 16x8 (which is what Hacker recommends) to 19x8 increases the power by (19/16)^5 = 2.3 times!

Lesson learned: 1) Follow the recommendations, 2) do a sanity check using a motor calculator, 3) once installed, ALWAYS check with a watt meter.

 

[Only Fine Helis]

So my follow up question would be why 3dhs would recommend a motor/prop combo that is 200-450 watts above the rating of the motor?

 

[Enterprise]

I was looking at getting the A50-14S and running a 18x10 as it is 425kv like the motrolfly. This looks like a plug and play option on the ebox from what I can tell.

This reminds me to get my gasser out sometime soon. It is a lot of fun.

 

[ryan_m]

So my follow up question would be why 3dhs would recommend a motor/prop combo that is 200-450 watts above the rating of the motor?

Because many believe that Hacker is somewhat notorious for under-rating their motors - at least when they are used in a 3d application. Since we tend to be all over the place with throttle usage when flying 3d, many get away with overpropping / over-watting their motors. Since we don't tend to stay at full throttle for more than a few seconds this usually isn't a problem.
However I suspect Hacker rates their motors more for continuous power, so if you were to run them at their suggested rating on full throttle you should be ok. Since we over-prop, you can't do that without killing the motor. At any rate, more factors enter into the equation too - motor cooling for example and ambient temps. If you were to run the same motor in 50 degree outside air you can pull more watts through it safely than you could at say 100 degrees. I learned that the hard way in my first summer of electric flying. Setups that ran fine all winter started killing off the motors in the summertime 100 degree temps. Safest thing to do is to measure the motors temperature and decide based on that whether you are over-propped or not. I like my motors to be under 130 degrees when I land. Hackers, maybe 140 degrees as they seem to tolerate heat better than others, or are made to run hotter depending who you talk to

 

[Only Fine Helis]

So I'm assuming that you guys have enough experience with the motrolfly 4325-425 that heat will not be as much of an issue? (Obviously it has a higher amp rating)

 

[njswede]

The Motrolfly 4325 should be fine. It can handle up to 2300W. I would start with an 18x8 and check the amps/watts. You should see around 2000W. If you see a lot less than that, you may want to try the 18x10. 2000W should be pretty nice on a 70" Velox, I think...