How to Install BK5001 HV servos on a supped up Trex 500L

[Alex M K]

Ok, I have been getting a lot of PM's from people asking me how I installed BK 5001HV servos on a Trex 500L.

This is in part, because of me saying I did so in a thread where I did a comparison between the DFC and the 500L.

A small insight on this before I go any further.

Why the Trex 500?

I travel a lot and always bring a heli with me, while the trendy OXY3 is cool and OK, its too small and too lame for me, and reminds me more of a micro heli toy than a real heli..I like it, but the way I set and improve my Trex’s 500, the Oxy, even running 4S with a 12 T pinion is an underachiever. Plus, I can’t see the damn thing.

I prefer the 500 size, and use it as a beater and as a “I have no love for you” practice heli to save my 700’s Mostros and Auroras.

So, and although the Trex being a slightly crappier heli, (note it’s still better than 75% of the rest of the Asian crap out there, no matter where in Asia they come from), it is a pretty decent helicopter to be honest..the frame that is.

The Trex 500 has many advantages for me, one being that easy to remove TT tail which makes it so easy to take it apart to put inside my checked luggage, I can be flying within 5 minutes of unpacking, no need to mess with the belt crap.

Second its durable as heck and handles crashes pretty well, third, parts are cheap and available anywhere (I am sure some local Walmarts even carry parts for them ), it is quite reliable, and above all, it actually performs quite well, if you spend some time with it and do a few modifications, mostly electronics.

Problem with it, is the electronics they come with don’t exactly fit my bill. While I understand they must do this to be able to offer a decent product or kit at a competing price against the other Asian brands, I personally think that while the frame is pretty good, the electronics suck (for me that is, and this is only for what I want it to do).

I am sure they are prefect for beginners and others, but for me no, thanks…the servos are so slow, I grow a beard each time I ask them to move (even in the 6V mode), the tail servo should be sued for lying in saying it’s a tail servo, the ESC its an underperformer, (it’s ok for mild stuff, if you fly on end points), but Governor? Forget about it. The motor can’t handle heat and high RPMS without falling off the helicopter, the FBL, well…I wouldn’t send it to Africa to help the starving by fear of offending them.

So although I do NOT add any add ons, any bling or any “hey look at me” stuff to the mechanical part of the heli, the frame, I do change all the electronics…and I mean all of them, starting with the servos..enter the BKs

On the frame, other than using a set of unbreakable Gorilla landing gears for obvious reasons , the Fusuno canopy grommets and using RCSrewz SS screws, because thy are the only screws that can handle all the assembling and disassembling I do, due to crashes), the frame is pretty much stock…I also don’t use the Align main blades, not because they are not good, but because I prefer “el Cheapo” Revolutions I get on ebay and on those I even prefer the Flybarred blades, as they make the heli more unstable and nimble and better performing, for me, off course. The tail blades are stock like everything else

So what do I change on the heli’s electronics?

This is how I have mine made and to be honest, nothing else I flew before matches this heli…including the over rated the trendy Euro stuff , that if you do not have now, you’re not a cool dude!

My cheap Trex 500L super machine is set up with this

• 1) ESC - Kontronik Koby 90 LV Brushless ESC, running a 14 T pinion at around 3200 HS for 4.5 minutes flight times

• 2) BEC- Western Robotics Hercules Super Mini BEC G2 running at 8.2V

• 3) BK 5001 HV servos cyclic

• 4) BK 7005 HV servo (need to change the servo cover to a standard)

• 5) Scorpion HK-3226-1600

• 6) Spartan VX1n FBL

So when I say this, people always ask me how the hell did I manage to put the BKs there, when everyone says its impossible.

Well…I had a crash yesterday and had to rebuild the whole heli, so I took some shots while rebuilding it for this thread, in case someone else wants to do it, and to save time responding to PMs

Plus...if you want to build a mean flying machine...this is it!




First (other than getting the servos, off course), you need to spend some money in a few things

First you need to buy these:


http://www.amain.com/rc-helicopters/...h50167/p215657

you will need to use the two 4.7 Linkage ball A (M2.5x3) (4.75x13.5mm) to put on the swash plate on the aileron side. The stock is 11.5mm and will be too short, and will throw the geometry off because the BKS have different sizes than the Alifgn DS515s



http://www.amain.com/rc-helicopters/...0094-1/p158587

you will need the two long Linkage ball D (3x3.5) (4.75x17.5mm) to install in the new servo horns bellow



http://www.amain.com/rc-helicopters/...bha050/p449573

you will need these to thread the longer servo ball links above, because the 17.5mm long ball inks are M3 and the stock BK horns are too weak and to keep the geometry, they have too be installed at 18mm form the horn axis, and that puts this on the last hole of the BK horns making them too weak.


Off course, you can use the Align stock red metal ones , tap a 3mm hole and be done with it, but I personally prefer plastic to save the servos in crashes



http://www.amain.com/rc-helicopters/...0075-s/p240265

now, these are for the SAB 700, and you need to have the wholes brought together to fit the smaller hole spacing of the BK servos, with a dremmel, gouge the holes towards the middle, and towards the center, and you also need to be reshape them to fit the space recess where the elevator servo attaches (see photo of how they should look bellow) Use one of the thin spacers as template



http://www.amain.com/rc-helicopters/...0572-s/p427874

Get at least 3 bags just in case...you will need them to tune the spaces right



These are the spacers I mentioned before the SAB 700 ones, you need to shape them to fit the elevator recess...you will need 8 of these 4 above and 4 bellow, to bring the elevator servo further out and 4, 2 each for the aileron servos.

if with 4 its too far out, use the thinner ones, and use 3 thick and 2 thin..I have done it both ways and works fine either way..you will have to test it.







as you can see the elevator servo mounts further in, this is because the stock align servos have a lower height from the tabs to the servo horn gear, BUT the BK is rather tall, so you will need to fill that void for two reasons..one is to center the elevator arm with the anti rotation piece, second to avoid having the elevator and aileron servos touching each other, as these servos have the motor protrude the case and if you don’t play with the spacers they the elevator case will rub on the aileron servo’s case.




You will also need to round the frames on both sides, in the front, with a dremmel, to clear the space for the servo motor. See bellow.







this is the difference between the 11.5 and the 13.4mm ball links both threaded M2.5






With the 13.5mm ball link on the servo arm, the elevator anti rotation arm will align PERFECTLY!








you will need at least 12 screws 15 or 18mm long and washers off course, for the aileron servos.




install the elevator servo first, because you will then see if the aileron fits ok without the servos touching each other...if they do, bring the elevator out by adding a thin spacer more.




then install the aileron servos, together with the thick spacer, if the servos are still touching each other on the motor, you will need to put one or two washers in the lower and upper front screws servo screws under the spacer, to give it a bit more angle..I use one washer only..test it with one and two..member only in the 2 front side servo holes!







When installed, the servos will both clear the shaft by 1mm, it’s perfect.



the elevator servo horn must be fitted with the 13.5mm ball link, and with this, it will center the arm perfectly with the SAB servo horns..other arms may differ a bit- use spacers accordingly





use the M3 17.5 mm ball links on the aileron servo horns, I use plastic horns and use a bit of CA glue to secure the links. with the 13.5mm on the swash the geometry falls right on! Look






For the tail BK 7005HV I did the same, the only problem is that it comes with a standard servo mount top case, so you need to change it, for this it takes 1 minute to replace and comes with shorter screws for it as well. --> http://www.helidirect.com/mini-size-...ail-servo.html


and need to Dremmel a space for the servo motor on the plastic housing




Anyway, hope this helps and if you have any more questions, please let me know.


All I can tell you is, set up this way, this is by far the best heli (short of myMostros) I have ever owned or flown…it’s a beast and outperforms any other heli you throw at it!!! With a cheap crash cost compared with the fancy trendy must have helis!!

(BTW...I had a DFC set up with BKs 5001 as well, and altough a lot said it was not psossible, I managed to get them in just the same!)



Kind regards

Alex

[SumOFparts]

You know you're gonna get a lot of flex with that servo horn and that 13.5mm ball link......

Had simular setup on my 550's and had to change - it was scary to watch it in operation under a heavy load........major flex.....

Though it was better to have geometry a little off - than a mid air failure.....or mushy response....

[Alex M K]

Originally Posted by SumOFparts

You know you're gonna get a lot of flex with that servo horn and that 13.5mm ball link......

Had simular setup on my 550's and had to change - it was scary to watch it in operation under a heavy load........major flex.....

Though it was better to have geometry a little off - than a mid air failure.....or mushy response....

SoP,

Do you have an idea of how many times this heli has flown already? And for how long it has been flying as is?

BTW, the stock original 500L has a 11.5 on the swash and 13.5 on the servo arms... 6 mm difference is nothing

[Alex M K]

By the way, one thing I forgot to mention, (and I will edit the thread later), is that due to the extra depth of the BK elevator servo, the stock canopy does not fit on the left side.

So I took one of these old braces I had from the 500DFC's (the stiffeners inside the frame) here is one of many I still have




cut the 2 ends off and made 2 small extensions tubes (these are all threaded all the way from the factory!), that bring the rear posts further out a bit,




here what it looks like



and bingo!






This also clears the top part for the rods, otherwise they would touch.



perfect fit.


BTW inside the canopy, where it might touch the servo in a crash I put some soft side Velcro to protect the servo and from vibration.

Initially a few months back, I was simply cutting a whole in the canopy and enlarging the area where the swash rods touched, but this extension mod works great and no need to cut the canopies.

Kind regards

Alex

[Kap'n Krunch]

post a flight vid of that 3200 hs for 4.5 minutes I gotta see it to believe it

[Alex M K]

I can either fly or shoot videos...still haven't mastered the art of doing both at the same time...I fly alone, normally no one around, but if I'll come across someone willing to do it, sure. Why not..actually, just checked, my timer beeps at 4:20

Kind regards

Alex

[Gladius]

Great write-up! Thank you for putting this together! Ironically, the only electronics on my 500 are still "stock" are the servos. (They aren't really stock, because I replaced the original plastic gears with metal ones.) For my skill level, they perform fine, but I'm getting to the point where I'm starting to think about getting something better.

BTW, I completely agree with you on the Revolution FB blades! I wish I could find some more. After reading your post, I checked eBay, but couldn't find any deals on them.

[Gladius]

Alex, what is the distance from the bottom of the mounting plate to the bottom of the servo on the BK-5001?

[Relisys190]

Nice work!

[Alex M K]

Originally Posted by Gladius

Alex, what is the distance from the bottom of the mounting plate to the bottom of the servo on the BK-5001?

G, I'm away from it for now, I'll let you know once I get near it, later on.

Kind regards

Alex

[Gladius]

Thanks. No rush, I'm just starting to think about upgrading my servos.

[Alex M K]

Originally Posted by Gladius

Thanks. No rush, I'm just starting to think about upgrading my servos.

Gladius,

if you really just want a better faster servo, and upgrade from the Align ones, I'd look first at MKS, Hitec and the smaller OMG (with OMG probably on the top of the list)..there is absolutely no need to go with these more expensive BK,s unless you really want them or need them..MKS makes a much cheaper almost as fast servo as BK and so does OMG..are the BK good? yes the best, and quite performing at that, but a bit on the high side cost wise.

Hope this helps save you some cash

Kind regards

Alex

[Alex M K]

Originally Posted by Gladius

Alex, what is the distance from the bottom of the mounting plate to the bottom of the servo on the BK-5001?

Ok, sorry for the delay,

from the bottom of the plate to the bottom of the servo its around 25mm



Kind regards

Alex

[Gladius]

Alex, thanks for the info. The frame on my ESP is only 43mm wide, so I would need 3.5mm of shims on either side, which is just a little too much IMHO. But those OMG servos look awesome! I'll keep my eyes open, and if some extra cash and a deal converge in space and time, I'll grab some.

[Kap'n Krunch]

Originally Posted by Gladius

Alex, thanks for the info. The frame on my ESP is only 43mm wide, so I would need 3.5mm of shims on either side, which is just a little too much IMHO. But those OMG servos look awesome! I'll keep my eyes open, and if some extra cash and a deal converge in space and time, I'll grab some.

I've been flying with the mks 9767 and they held up great zero slop and quite a few crashes and have never striped gear

[Kap'n Krunch]

here's a great vid of the 9767s

Dunkan Bossion testing the new MKS HV9767 for helidigital (3 min 6 sec)

[SumOFparts]

Originally Posted by SumOFparts

You know you're gonna get a lot of flex with that servo horn and that 13.5mm ball link......
....

https://www.helifreak.com/showthread...72#post6619872

[Alex M K]

Originally Posted by SumOFparts

https://www.helifreak.com/showthread...72#post6619872

Sum thanks for your reply

Ok, let me see if I understand what you mean, because I think you're talking and linking about 2 different things at the same time.

1st you said the flex in the horns, then 2nd show a thread of a ball link failure in the thread, when these are not the same ball links.

so what are you saying fails? the horn or the ball links? My links are 2.5mm threads, the ones in your link are 2mm.

I have absolutely no flex with the servo arms I am using the SAB ones, with the 13.5 ball links that have a 2.5mm thread, (not a 2mm thread like the ones in the link you provided), and I have never had a failure or an issue with this arrangement. It's been 6 months now, nil, nothing!

BTW, so you know, the heli in these pictures is still flying 3 to 4 lights a day, with these servos and horns/ball links arrangement..I made this thread in june or so, and modified the heli in February, and its still here.

So far, and until now, I never had any issues. I did crash it several (many many) times, and only broke one servo arm. Everything else is as is.

1) I have absolutely no flex with the servo arms I am using
2) the 13.5 ball links have a 2.5mm thread, not a 2mm thread like the ones in the link you provided.
3) I have never had a failure or an issue with this arrangement.

Kind regards

Alex

[SumOFparts]

I apologize for my persistence - and applaud you for teaching us..

Its just I'll noticed a great deal of flex on my 550 models using similar configuration......so did my best to eliminate that distance.

I'm also interested in limits and thresholds that others can get away with..

Think this would give you little more give in a mishap.... . anyhow keep the faith - many will post in future - and I'll be there to ASK....99% of my knowledge base is from listening and asking you guys......

thanks

[Alex M K]

on the contrary, I am not teaching anyone.

I just posted and shared what I did to turn a rather neutral, null, boring, and mundane helicopter into something really powerful and performing, that outperforms most 500s out there, for real.

So this is more a "I did this to that", rather than a "do this or that". I don't really care what people do with their helicopters.

And no, I did not experience any flex or issues whatsoever, with these servos/arms/ball links. That's the point I was making.

I don't know, and never had a 550, so I can't tell or debate about its issues, this one I butchered is a 500, so perhaps there is less loading in the disk


thanks again for the input

Kind regards

Alex