42-50-800kV equivalent
 

Going to buy a Electrostik. Have most of the stuff but need a motor.. What is an equivalent to a 42-50-800kV motor. I could not find an answer on HK or Hpartz website. Thanks

PS. Have some Turnigy HXT900 servos. Will they fit the bill?

Equiv to the rimfire, you mean?

http://www3.towerhobbies.com/cgi-bin...1&I=LXLWV3&P=3

REQUIRES: Brushless Motor-compatible 45 amp Electronic Speed Control
Propeller: 12x6 - 13x8 electric
SPECS:
Motor Diameter: 1.7" (42mm)
Motor Length: 2.0" (50mm)
Shaft Diameter: .20" (5mm)
Shaft Length: .67" (17mm)
Lead Length: 3" (76mm)
Connectors: Bullet type, 4.0mm diameter Max.

Constant Current: 50A Max.
Surge Current: 80A Max.
Constant Watts: 925W
Max. Burst Watts: 1480W
No Load Current: 2.6A
Input Voltage: 11.1-14.8V (3-4S LiPo)
RPM/V (kV Rating): 800 Weight: 7oz (198g)



?

What a weird spec. To get 925W at 50A means they think they can get over 18V from a 4S battery.

And how about Constant current 50A max, Surge current 80A max but it only needs a 45A ESC ?

Either they're trying to sell a lot of ESCs or they're just having a laugh ;).

Steve

I think it means you can prop it up to those specs or pull amps till it fails on you.... Hmmm

Just ran the Rimfire numbers through www.motocalc.com.
Motocalc suggests running this motor at the peak currents of 80 Amps will burn it up. Even running the motor at the 50 Amps continuous rating will result in motor efficiency of only around 50%, and winding temperatures of over 400 F. It's going to get hot if you run much more than 40 Amps through it. This rimfire motors windings measure out at 0.036 Ohms. So at 80 Amps, you're loosing 230 watts in the windings alone. (P = I Squared times R)

This motors specifications indicate maximum burst watts is 1480. That is 211 watts per ounce of motor weight. IMHO, anything much over 100 watts of power per ounce of motor weight might be pushing it a little. And doing so usually results in the motor efficiency dropping like a rock.

FYI, one of my models recommended a 400 Watt or so Rimfire motor, with the warning not to touch the motor after a flight, because of the risk of burns. :confused:

As a comparison, a $$$$ Hacker A40-10S motor will run at 89% efficiency while pulling 52 Amps on a good quality 4S Lipo. This motor weighs in at 9.4 ounces, with a winding resistance of 0.007 ohms, about 1/5th the winding resistance of the Rimfire. That, just turns into heat, not turning the propeller. http://www.aero-model.com/Hacker-Brushless-A40-10S.aspx

I now have 8 of those $$$$ Hacker motors, ranging from an A30, two A40's, three A50's an A60-16M, and a new A60-5S. Every one of them performs to their specifications, and to their current and watt ratings without issue. (Just got the A60-5S, have not run it yet.)

Any good quality motor that gives winding resistance measurements of perhaps 0.01 ohms or less, with similar 8 or 9 ounces of motor weight should perform well. There are a lot of those good motors out there. Problem is, more than a few of the "cheap" motors don't provide the all important winding resistance information.

Well that is obvious you do not wanna use this application in a heavy plane... Well do not use 4s, as most folks see the size of this motor and think 4 cells.... 3s is a better answer ... The hacker you mentioned... What is the can length and kv rating?

The web page shown above indicates 1.65 inches diameter and length, with a 750 KV rating. Hackers come in a wide variety of different "Winds" for the same motor frame, Hacker A40-10S, A40-12S and so on. The A40 series motors run from 410KV to 750KV. And up to 1500 Watts for the "L" long motor. I ran an A40-10L motor at 65 Amps on a 6S2P A123 pack, pulling about 1200 watts on an 8 pound P51 model. It really hauled the model around. Went to an A50 on that model though, just did not feel comfortable putting that big prop on that motors shaft. That motor got me over 100 Mph on a Revolver model before an aileron came completely out of the wing. Still flying that motor in a different model today.

This motor is only about $15 more than the Rimfire motor.

not bad for 4s and 750kv... I love learning about motor windings... --- kyleservicetech --- could you answer this bugging question in my mind???? I always wonder the pluses and minus of wire gauge in a winding, the way it is delta or the other, and if the magnet strength have any effect? --- Scott

It's not so much the wire gauge, as it is filling completely the steel slots for the windings. The motor manufacturers often use multiple strands for each "Conductor". The reason is, even though a single strand could wind up with more "Copper" in each steel slot, you can't bend a single large strand of wire around the corners, without the varnish flaking off.

Some of the real cheap motors don't fill the steel slots, because that takes time, and time is money. Those motors can have lower efficiencies because of that.

As for delta or wye, either works well, and three phase power transformers can be wound either way. Most commercial three phase motors are wound in delta. And most of the model bushless motors I've run across are wound in wye. Which is better? It really does not matter, because going from delta to wye in a given KV rating simply requires the use of different gauge, and different number of turns in each magnetic slot.

As for magnets, the reason our brushless motors have the power they do is because of the very powerful magnets used. The higher the magnetic strength of the magnet, the less turns of magnet wire you need for a given KV rating. Less turns means you can use heavier gauge wire, making it possible to run even more current through it.

Using those ferrite magnets in our high powered motors would not work out well. The magnetic field of a motor pulling 50 Amps plus would demagnetize those ferrite magnets.

You have really great info and knowledge..... thank you very much for this.... I will run into you in the other thread (power systems) for any other questions.... Thanks again:) --- Scott

Yup.. I was looking at a Turnigy 32 and a 60amp ESC. Would that do the trick? Thanks

Thanks Scott
Back in the mid 1980's before high powered motors were available, I was taking burned up brush type motors from work, rewinding them for more power, and putting them into models.

These were 24 volt permanent ferrite magnet type motors. The iron slots in the armature were only 1/2 filled originally by the mfgr, I managed to double the motor efficiency by actual dyno tests by filling the iron slots with heavier wire.

Problem was, the motors commutator for the brushes could not handle the extra current, and motor life was only a few flights before a meltdown. These motors were running about 15 Amps at about 20 volts.

Astroflight came out with their cobalt high powered brush type motors, and those motors from work were not even close.

Now we've got brushless motors, where even the lowest cost cheap China motors far outperform the very expensive Astroflight brush type motors typical of the 1980 to 1990's. Of course the Astro motors used top quality steel, bearings and so on. but my last Astro 40 brushless type motor used a brass gear on the motor shaft, and an aluminum gear on the prop shaft. That setup didn't last more than 40-50 flights before the gears were worn out. And I totally enclosed the gears with a top quality gear lube.

How times have changed in the past ten years.

If the specs generally line up, it should be a good replacement.

Always assume you don't want the max worst-case burst amperage through the ESC to be more than 85% of the ESCs rating is the policy I apply.

So, make sure the max amps of the motor is less than (0.85 x ESC rating).

Dave

Thanks Dave... I have some old 9G servos.. Will they work or should I get bigger?

That goes out of the very limited area where I know much, if anything...


Dave

If you're refering to the weight of the servo as 9 grams, I'd not use them. You are working with a model with near one horsepower up front in the electric power system. So, models for this size motors should be using standard sized servos, with torque ratings of perhaps 50 inch ounces or so.

Nowdays, even name brand standard servos are pretty reasonable in price.
http://www3.towerhobbies.com/cgi-bin...&I=LXXCZ9&P=ML

Thanks all for your help. Bottom line.

Turnigy 32 outrunner
45a ESC
Hitech 485 servos
3200mah 11.1 20C Lipo
Spektrum sport 500 receiver

Have I missed anything? Thanks again....

I would say you want to bump up the ESC size a bit.

They recc a 60A for that motor.

Dave

Might be a good idea to run your numbers of your model and power setup through www.motocalc.com.

That Turnigy motor is rated three to four LiPos, so with 4 LiPo's, an 12/6 prop would be in the ball park. Motocalc suggests the Turnigy motor will turn this prop around 9700 RPM, 47 Amps, 13.8 Volts 650 watts, 86% efficiency, and putting out about 90 ounces of thrust on the ground. Raqte of climb is esitmated at about 1700 feet per minute, based on a total weight of 73 ounces.

All in all, for that motor, and that model, pretty good.

Thanks... Just what I needed... Much appreciated to all that helped..

Is this your first electric? And do you by chance have a Spektrum DX7 transmitter?

One thing about these electrics, once the motor is armed, moving the throttle results in instant power. And that Turnigy motor has close to one horsepower on the prop.

The DX7 transmitter is one where you can mix the throttle with one of the other transmitter toggle switches, so the motor is dead unless that switch is in the proper position. I found a way to do this with the DX7 on the Internet.

Bad things can happen, if you're playing with the servo directions on your transmitter, and accidentally reverse the throttle. Instant full power.

As an added safety measure, whenever doing any fiddling around with your electric model, TAKE THE :censor: PROP OFF!

I do have a DX7 but have not gotten thru all the programming yet. I am on my third electric. Started with a converted baby ugly stik that used to have a Cox .049 on it. My second one is an apprentice 15E and have graduated to a parkzone wildcat. When I stumbled upon the electrostik I knew it had to be my next plane. I always loved the way they flew. If I could find an old Sig Kommander I would be in seventh heaven. One of my real favorites....

The info below is not original, I found it in the Internet. Following these instructions, that makes your DX7 transmitters "Gear" switch a motor throttle kill switch. Make certain to place the throttle trim to zero, or throwing the gear/kill switch results in a minor throttle shift.

Electric Flight Safety
Ideally every electric aircraft you have should be equipped with an arming device on the craft itself (either and ESC switch or power interrupter plug) as well as having a throttle cut switch on your transmitter. Since electric motors can startup unexpectedly and inflict a lot of painful damage the double precaution can avoid some nasty injuries. Although an arming switch/plug on the aircraft ought to be sufficient on its own there are times when it is armed with the intention of flying but something distracts you and the aircraft is now vulnerable to a careless jog of the throttle lever, the transmitter becomes your last line of defense.
I have implemented a transmitter disable switch for all my aircraft (helis as well as conventional planes) this way the process is second nature to me. The idea is that whenever the aircraft is not expected to fly the transmitter switch is in the disable position. The moment before takeoff I switch it to enable, fly as required then the moment the aircraft touches down and I have completed taxiing it I always click the switch to disabled.
Some of the more advanced transmitters have the ability to set a throttle cut switch up within their menus however others need a little work to make it happen. Below I give the process needed to set up a Spektrum DX7, it is likely this technique can be used on other transmitters, it is well worth doing and if you are still unsure how try looking online for your particular transmitter.
In my case I use the switch at the top right hand corner of the transmitter as the kill switch, this seems to be a standard as far as I can tell, the DX7 does have a label saying HOLD for this switch (as well as Ruder D/R).

Setup Process For the Spektrum DX7 Transmitter:
From your selected plane setup menu (pressing scroll and select simultaneously) move to one of the mixing channels (I used Mix 3, for mixing with the gear switch - kyleservicetech).
Select source and destination for the mix to be THRO (short for throttle), the display should show:
THRO -> THRO
Now move to the rate section and set both sections to -100% (you will be able to set one of them with the throttle stick down and the other with it up).
Move to the SW: section and set it to MIX
Move to the OFFSET section and set it to -100%.
If you toggle the gear switch you should see the text to the right of the THRO -> THRO change from OFF to ON, when this reads ON the throttle is disabled (this should be with the switch pulled toward you).

[PROG.MIX1]
THRO->THRO ON
RATE: -100%
-100%
>SW:MIX
OFFSET:-100
Carefully try this out with your model turned on, with the switch toward you it should not be possible to start the motor at all (even helis should be disabled despite the position of the idle up switch). And, as always, check all remaining transmitter functions for both direction and unexpected operations. In case something else got changed by accident.
All that remains now is to cultivate the habit of ensuring the switch is in the disabled position whenever you pick up the aircraft and whenever it is not on the flying field.