AK2M4 / XT Brushless Motors

[Fatboy40]

@ak2m4 thanks, and there's no reason for a return, I know it will work fine in my MP5K when I buy a GATE Titan v3 to go with it 😃

 

Regarding batteries I use 11.1v Titan Li-Io's mostly, but tested this with a Nuprol 11.1v Li-Po.

[ak2m4]

@Fatboy40 I'm still a little concerned over why it wouldn't work with the DE Falcon, I don't have one here to test myself so might try getting hold of one.   I remember seeing a YT video with the Warhead on a M904 and it worked ok, apart from the 7.4v wouldn't spin I think, also the motor was a little too large for the grip.

[Fatboy40]

Online people have been 50/50 with brushless motors and Falcon controllers, some perfectly fine and others nothing at all.

 

Personally I've tried my best to talk to the manufacturers about many DE related things, I've reached out to "Fujian Qing An Precision Machinery Manufacturing Co. Ltd." and all the other variants of their name via loads of channels, and only a couple of times have they ever replied. Obviously the Falcon is built to a cheap spec / BoM, however there will be firmware present but God knows if later manufactured DE M900's have differences in the versions (for example the DE M904E went out of stock globally for a good four to six months at one point, and if one of the shortage was the Falcon there 's a chance they made a revision to it).

 

[Pseudotectonic]

3 hours ago, Fatboy40 said:

a nice spin and then the Falcon giving two beeps

If it is this same model then two beeps means voltage problem, it says operation voltage 6 to 14 V so it could very well be the battery cannot maintain 6 V, maybe the current was too much amps so the battery Vdrop in protest, maybe the gearbox was not shimmed well so there is extra resistance, maybe the spring and gear ratio combo represent too much torque requirement etc...

[Sewdhull]

I fitted mine to test and it functions just as the brushed motor does.

I have a perun.

Motor height was different and it needed to be screwed in further.

It fit without issue

I think perhaps I'll look at bevel height as I've got motor tower play which I removed on the brushed motor. Or shim the tower to fit the hole in the gearbox casing.

I haven't fired any bbs through it yet but it fires normally on 7.4 and 11.1 lipo, a 7.4 lion and a 9.9 life.

[Sewdhull]

As a motor, the brushless is 1mm shorter, compared to the xt brushed, from the motor front to the pinion end, the motor tower has no play in it. Altho I would suggest this dimension could be adjusted as the shaft was probably a bit longer originally.

The motor appears to have strong magnets, and the stepping between them very apparent when you rotate the motor.

Motor tabs are strong.

I notice the tabs are nearer the motor ends, which caused me no issues but may in different grips at the end. There is room to bend the tabs through 90degrees which is an option you don't see usually. Don't bend the tabs lol.

I'm really happy with this motor so thank you xt.

This weekend I'll run this and the xt brushed through the ammeter and see what that reveals.

[Fatboy40]

1 hour ago, Pseudotectonic said:

If it is this same model then two beeps means voltage problem, it says operation voltage 6 to 14 V so it could very well be the battery cannot maintain 6 V, maybe the current was too much amps so the battery Vdrop in protest, maybe the gearbox was not shimmed well so there is extra resistance, maybe the spring and gear ratio combo represent too much torque requirement etc...

 

It was tested outside of the pistol grip, so no gearbox to spin up at all. The battery was at 11.83v at the time, and 11.77v now, so should be enough.

 

I need to try it tomorrow using a GATE Titan v2, with the same battery, and see what happens...

[ak2m4]

@Sewdhull thanks for the amp test, I did do one a few months back but someone else doing a test would be most appreciated. The overall length when they came from the factory was a smidge longer than I liked but really I don't think it matters too much, I might just send out the ones I have left out at 88.6mm, on the 2nd batch maybe reduce the length to 87/88mm

XT= 88.6mm

T238 = 86.3mm
Warhead = 87.8mm
SHS = 88.1mm

Edited February 24 by ak2m4

[ak2m4]

Photo of the innards today, my test motor had a faulty bearing after I applied too much force when initially fitting the pinion.   Seems the worst thing which will happen is the rear bearing will fail and cause the performance to degrade, pretty simply fix. 

[Pseudotectonic]

Just wondering how much of customization can you do with your OEM, can you specify the firmware features and even how to implement the variable speed change? Maybe magnet types and winding counts and number and positions of bearings?

[ak2m4]

1 hour ago, Pseudotectonic said:

Just wondering how much of customization can you do with your OEM, can you specify the firmware features and even how to implement the variable speed change? Maybe magnet types and winding counts and number and positions of bearings?

 

It's possible on most, winding counts and magnet a definite yes, position of bearings hmmmm not sure, where are you thinking?

They're a RC motor factory and this is their first venture into Airsoft, my guess is a fair amount of the components they buy from a factory.  At the very least I can ask and they will say yes or no, or that will cost £££ extra.   At the moment they have only just got back from their new year break so still waiting on the full specs.  My overall aim is to have a reliable brushless motor under £80

Edited February 25 by ak2m4

[Pseudotectonic]

@ak2m4 Winding count: I don't know how much exactly but I would imagine this is similarly balanced between torque and max RPM, what is the highest winding you can get for a say max 30k RPM? Because it seems to me 30k is high enough even for high ROF builds before you run into problem with other things not catching up

 

Magnets: it seems Chihai is moving towards higher grades with higher temperature ratings which makes sense, so ideally you want highest grade with highest temperature rating, but I imagine this is only limited by cost. What are price differences of say N35/N52/N35H/N45SH/N45UH?

 

Bearings: I think if you have an integrated CNC tower like what Chihai is doing, you can probably copy their three bearing config (like this), I don't imagine more bearings are automatically better and I think the three bearing might already be optimal

 

Electronics/firmware: for airsoft it might actually be better to have a "dumb" motor that only has basic current limit, because of mosfet compatibility, I think the trend of putting more features into the motors might not be sustainable because there are only more and more ETUs in airsoft

 

The bells and whistles would only make sense if people are using brushless without mosfet, but more often than not that is not the case

 

To be "dumb" I mean

 

1. it needs to pass some current at rest so it is visible to the mosfet when plugged in (not sure about this)

2. work with lower range voltages because of voltage sag in airsoft batteries

3. able to work with reverse polarity

4. able to work with PWM input

5. able to work with 3+4

6. no startup delay, not sure how to achieve this, you want to keep the controller powered at rest so it doesn't need time to wake up, maybe with a capacitor as suggested

7. I don't really see the use case for speed control, if it is not using the maximum speed the magnet and winding can output maybe it has room to put in more winding for more torque, and if you have different speed models you can individually tweak this, and probably sell more (like Warhead), and arguably speed control should be something done at ETU level, the motor should be dumb and just let ETU do its job, the motor should just be responsible for spinning and IMO the electronic should mimic the behaviour of a brushed motor as much as possible

[Sewdhull]

The motor has to follow the same form factor as existing motors and a single case for long and short motors makes sense, at least for the smaller producers.

 

I don't think there's a case for a reversable motor, unless you can think of a reason why you'd want such a thing.

 

Brushless motors can't be very dumb, they need the controller, the large flat chip, to do the sums to make it turn etc.

You need additional wiring terminals to do anything via the ETU because 1, the ETU expects to deliver only voltage to the motor terminals, and 2, the motor expects to see voltage only to the motor terminals.

You may find the motor controller already brakes the motor to control the back EMF at motor stop.

 

Given the right message the motor can spin any way you want it to but you'd need some sort of interface to achieve it and the controller programming and it needs power.

 

 

 

[ak2m4]

@Pseudotectonic Not sure on the magnet prices but traditionally in brushed motors this was always the biggest single cost.  Windings and thickness of wire can be flexible from what I know.

The integrated tower is a nice idea but you'd also have to make a new MIM body for the brushless, this would be a huge cost, would need to open a new mold etc.  The "dumb" motor is a really good idea and could help in lowering the price however from what @Sewdhull says it needs a certain level of intelligence in order to function.  However there's no harm in asking the question to the factory.

 

 

Edited February 25 by ak2m4

[Sewdhull]

You need some sort of electronic commutation and sensors plus a lil computer to work out when to commutate.

 

The main difficulty in making the BL motor like a brushed motor is that the BL needs power to work, MOSFETs have a polarity and the board needs electrical protection that Brushed ones don't.

 

There's a circuit on the board to supply power to the electronics and the tab voltage will go via the MOSFETs to the windings switched at the right time to make the motor spin the right way using the sensors on the endbell.

 

Made the right way you can power the device with PWM, switch the MOSFETs on and let the windings see the PWM signal. 

It is likely however that fault conditions will be detected if the averaged voltage drops in the PSU.

MOSFETs must have enough voltage, from the PSU via the controller not the tabs, to fully turn on or they get hot and magic smoke escapes so this condition is avoided.

 

The PSU should be polarity protected but the MOSFETs can't be because of the diodes protecting the MOSFET from the motor.

 

I noticed the perun load the motor to detect it making it try to turn. If other ETUs don't do this correctly for BL motors that's not the motors fault. ETUs need to bear in mind brushless motors exist.

 

BL motors can brake themselves with a change in timing and probably do, which will always make AB a problem on them.

If the AB MOSFET on the ETU shorts the motor it will stop doing things and no braking will occur when the MOSFETs are off. If the motor is shorted in pulses, to lessen the effect of the braking then the MOSFET may remain on if the PSU still has power and there may be braking. 

 

If braking is effected by reversing the polarity then this is bad news and magic smoke may escape.

BL motors may detect shorts to prevent damage and stop working with any AB.

 

If AB is to be effected on a BL motor the motor should do it, and could with the right programming and circuit.

 

 

I notice the board has a 78L05 regulator on it and some other PSU bit around the +tab.

That reg has a minimum input voltage of 7v (there will be wiggle room) to regulate 5v out.

 

[Sewdhull]

Currents, 7.4 and 11.1

 

22tpa xt 17 and 25

BL xt.      15.5 and 20.5.

 

Ah I forgot to take precocking off...wondered why auto was so similar to semi if not a little more.

 

The BL is much faster, esp at 7.4v in comparison, but I haven't sorted my feeding issue.

BL motor isn't fitted properly I can tell, I'll have to have look see when I've a bit more time.

Edited February 25 by Sewdhull

[Fatboy40]

The CYMA MP5K motor plate fits perfectly...

 

https://i.imgur.com/7ScBKmn.jpg

 

... so that's me off to buy a GATE Titan v3 then and not tell my wife 😬

[dlusted]

Took the plunge and purchased one myself.

Slowly upgrading my ARP9, and I've done everything outside the gearbox apart from the motor.

 

Was looking around at different reviews of brushed, but when I saw the XT Brushless for a good saving compared to other brushless; it's a good chance I'll take.

 

I've done RC in the past, and love the benefits of brushless.

Thanks @ak2m4 for giving such a good discount, granted pre-production.

[ak2m4]

45 minutes ago, dlusted said:

Took the plunge and purchased one myself.

Slowly upgrading my ARP9, and I've done everything outside the gearbox apart from the motor.

 

Was looking around at different reviews of brushed, but when I saw the XT Brushless for a good saving compared to other brushless; it's a good chance I'll take.

 

I've done RC in the past, and love the benefits of brushless.

Thanks @ak2m4 for giving such a good discount, granted pre-production.

 

thanks, let me know how you get on.  I'm still waiting on the factory to give me the specs for this batch, however this weekend I've got a little time so will do my own no-load RPM for both speeds.

[ak2m4]

Just tested the RPM of the test Brushless motor,

 

11.1v Turnigy 15-25C (Battery around 85% full charge)

Fast = 34K

Slow = 30K

 

Only 12% difference give or take with a 11.1v  

 

7.4v Turnigy 15-25C (Battery around 85% full charge)

Fast = 20.5K

Slow = 19K

 

Hardly any difference. 

Full stats coming Monday fingers crossed.  I also got some Perun's in stock so I'll be able to run some full tests with one of those.  

[Lozart]

Fitted the motor to my SCAR at the weekend, it's not completely back together yet but yeah...gun go BRRRRRTTT!!!

 

Had to modify the grip baseplate to get any sort of adjustment though. 

Any idea on more stock?

[ak2m4]

5 hours ago, Lozart said:

Fitted the motor to my SCAR at the weekend, it's not completely back together yet but yeah...gun go BRRRRRTTT!!!

 

Had to modify the grip baseplate to get any sort of adjustment though. 

Any idea on more stock?

thanks for the feedback on the grip base plate, I'll add that to the description.  I have more motors but for now I'm holding them back and waiting on more feedback, just in case. 

[Colin Allen]

6 hours ago, Lozart said:

Fitted the motor to my SCAR at the weekend, it's not completely back together yet but yeah...gun go BRRRRRTTT!!!

 

Had to modify the grip baseplate to get any sort of adjustment though. 

Any idea on more stock?

I had the same experience this evening; due to the shape of the end of the motor, the grip baseplate needed serious alteration to enable adjustment.  Other than that, I am very impressed so far; it runs quietly and seems efficient.

I will probably mess around with AB and precocking on the Perun tomorrow night to see if I can break the motor,

[Leo Greer]

Break it! Break it! Break it!!

 

I’ll confess, I’m still too scared of trashing a $100 motor or $75 ETU to try my T238 and Perun together. Some lovers are just never meant to meet, and you don’t know until they blow up. 😉

[Sewdhull]

My understanding of precocking is that it's just a delay in removing power after the trigger is released.

This won't affect the motor or MOSFET.

 

AB is more problematic, if it's shorting the motor it's possible to damage the motor electronics and no reason to suspect AB even works on a brushless.