450 Tarot Zyx-s2 3-axis Gyro Vs Mini Kbar

[murankar]

Yes there are work arounds for the power issue on the MIni V. The only time this is an issue is with power hungry servos. Keep in mind "POWER HUNGRY SERVOS" , not all servos are power hungry. Savox and BK servos are known power hungry servos.

As for confusion; I dont think I am confused as to what I am saying. I know what I have heard about the problem.

Look I am not trying to agrue with you over this. All i know is that the mini V has known issues and all I am trying to do is bring awareness about the issue.

 

[k8idx]

My Kbar hasn't arrived yet but I have some thoughts I would like to express here after doing some reading. The Mikado site has allot of very good information on it. They even show setups were there are different voltages on the tail servo and cyclic servos. This is an excellent idea. According to the Mikado site it seems that power supply issues are more common on 450 helis than on larger ones. This makes sense when you consider that everything is smaller on a 450 vs. a larger heli. They say to use every output from the receiver to the Vbar including unused ones. This increases the current carrying capacity of the power supplying wires by adding more of them. It's a good idea but I'm in favor of making a power distribution buss. I may even have two bec's on my heli. The problem is voltage sag while the servos are drawing the maximum current. This voltage sag can be low enough to cause a complete restart of the receiver which could easily cause a crash. (Read what Mikado says about receivers putting out full negative pitch signals during a restart.) In a FBL heli the flight computer (lets face it it IS a computer) can change the servo direction many times a second. That means that the servo motor has to come to a complete stop then start running in the opposite direction. Motors draw the most current when they are just starting up. With this happening over and over as the computer demands maximum current could be demanded even when hovering! My tail servo can run on 8.4 volts. My cyclic servos can run on maximum of 7.4 volts. If using a single power supply like the bec in the esc everything has to run at one voltage, the maximum voltage for the part of the system that can handle the least voltage. In my system this is the receiver which is rated at 6 volts. I was going to buy a new hi voltage receiver but I realized this might not be the best way to deal with the problem. I should mention that a conductor can deliver more amperage as the voltage increases so it is a good idea to run things at the maximum safe operating voltage. If you run the esc's bec at 6 volts and power the receiver with that, then run one or two separate bec's to the tail and cyclic servos then everything can run at it's max voltage and you have several current carrying paths which increases the current supply to all of the components. The Castle 10 amp bec is timy and only weighs a few grams. adding two of them one for the cyclic servos and one for the tail servo would be easy to set up and all of the current bottlenecks are eliminated. The only downside to this idea is the added weight of extra bec('s) and wires. I'm not claiming that this will work or that it will solve any supply problems but so far I haven seen any reason why it would not work. There are smaller lighter bec's available too. I used the Castle bec as an example because I have several of them and I've used them before in my fixed wing aircraft and I've never had one fail and they are easy to program, and they can make 10 amps. Noise due to the switching regulators might be a problem but that could be easily solved with a ferrite bead. If there is some glaring problem that I have overlooked please let me know. I'd love to hear your thoughts on this method.

 

[Smoggie]

I think you are over thinking it. Honestly, on a 450 if you use a decent ESC with a solid switching BEC (I recommend the Hobbywing V3 or V4 range) you wont have any issues.
Running dual wires to the FBL is standard practice on larger helis (say 500+) but is more about reducing voltage drop in the connectors. The individual servo type connectors are only good for about 5A or so continuous and maybe 10A burst, so for larger helis it's standard to feed power in via dual connectors. A few FBL have high current input connectors to get over this limit but using dual connectors works fine. On a 450 a single wire and connector is all you need.

The castle 10A BEC is a good little unit but unnecessary on a 450, you will be fine as long as the BEC in your ESC is good. For example the BEC in the Hobbywing 60A V4 ESC is rated for 25A peak, so more than twice as much as the Castle 10A BEC! At all costs avoid using cheap ESC's with crappy linear BECs.

 

[Smoggie]

Uri, I wasn't meaning that you were confused. What i meant was the confusion/contradiction between what you had heard and what I've experienced (and I do use high performance servos) may possibly be explained by the fact that there are two different types of mini Vbar, the older black type and the newer 'Blueline'. According to Mikado themselves the former is unsuitable for large helis and the latter is suitable. So in effect we are maybe both right, it depends on what version of the mini Vbar is being talked about.

I know there was some chat/speculation on forums a few years ago on the current limits of the Vbar power bus but as i recall it turned out to be something of a 'red herring' in that the real problem was not the current limitation of the Vbar but transient voltage fluctuations caused by EMF feedback from certain servos and/or BECs themselves not being able to supply enough current. The EMF feedback problem only effected satellite receivers connected direct the the Vbar satellite ports and powered off the Vbar's internal 3.3V supply. It's not an issue if using a standard receiver that doesnt take power from the 3.3V internal supply of the Vbar.

Mikado did their own testing which was I think in large part to demonstrate that the problem was not with the Vbar itself but with the servos and/or BECs. The tests are interesting reading:
Servo feedback issues: Hints regarding Servos | VStabi
Power supply issues: Power supply | VStabi

A capacitor usually does a good job of protecting against both of these issues so is good insurance. It may well be that Mikado did something in the Neo to give it better resistance to these issues (added a capacitor internally maybe?). I cant comment as i dont really know the Neo very well, but I have used lots of previous generation Vbars.

Lastly here's a post taken from another forum from MikadoUSA tech support on the satellite brown-out issue:

The issue is not Mikado, the issue is super high current servos that draw way too much amperage and back flow current into the VBAR. Some servos get awesome specs by designing and building great servos while a lot of the newer companies do that by putting a "bigger badder" motor in the system without thinking about what that does to the overall electronics in a Heli. The best fix is buying better servos (just cause some are expensive does not mean they are good/better) that way the system is not taxed beyond what sometimes even a direct 2s lipo can deliver.
Next is an external rx. That will take the rx power supply and make it before the VBAR so the regulator simply does not have to regulate the sats.
Lastly add a capacitor. Although some have had success with this, it is not the solution all the time. In some setups it works and in some it simply does not. A lot of experimentation is needed in this arena.
Hope this helps....Ron
__________________
MikadoUSA Tech Support

 

[k8idx]

I think you are over thinking it. Honestly, on a 450 if you use a decent ESC with a solid switching BEC (I recommend the Hobbywing V3 or V4 range) you wont have any issues.<snip>

I think you're right. When I reread the articles at Mikado I realized they were talking about helis that were going to be or were converted from flybar heads. It's fairly obvious that these are old problems that have been addressed in newer versions of the electronics. You have to understand that I am fairly new to helis in general although I do have an old 450 Trex clone flybar heli that is still flyable. All of the newer flybarless systems are completely new to me.

I did get my Kbar and I looked it over pretty well. The first thing I noticed was that the PC board layout makes allot of sense considering the power supply issue if there is an issue. Actually I doubt that there is. The traces on the board are not large enough to carry 5 amps or more by themselves but the manufacturer did something that I have seen many times on PC boards in the past. All of the current carrying traces have a generous coating of solder which increases the cross section of the trace many fold. This may sound like a cheap fix and it is. It is also a perfectly valid one. 5 amps should be no problem and my guess (I haven't done and measuring or math this is just a guess) is that even 7 amps or more should be okay. Now I just have to figure out how to install this gadget and program it. I have to say that I really don't appreciate the necessity of using Mikado software to program another company's product. This is only possible because of the unfair patent and copyright laws in china. Otherwise Mikado would have an easily winnable legal case against the makers of the Kbar. In Europe or here in the states this sort of cheap knockoff would never make it to market. Since I already have the Kbar I'll use it but as soon as I get the $$ together I'm going to buy the genuine Mikado Vbar. After all they deserve the business having originated the product. I'm sure they spent a large sum just developing and testing the Vbar line. The next heli I buy is going to be a Mikado. I'd like to get 600 or 700 size heli and after looking at their product I was very impressed. Their helis are beautiful. As nice as my Gartt heli is it's nothing by comparison. The Gartt will be a good product to learn on. If (and when) I crash it, it'll be cheap to fix and if I destroyed a Mikado I'd be tempted to cry over such a beautiful machine being destroyed.

Anyway so everything is okay with the traces on the Kbar and I've learned allot in a short time. Thanks to everyone who replied and offered helpful info. I'll post again after the maiden flight of the Gartt. Good lift everyone.

 

[Smoggie]

Building up the traces with solder is exactly how they do it with the genuine Vbar (both mini and full size are the exact same). Some well respected 'RC gurus' have tested those to 30A or more. The weaker point is the regulated 3.3V rail that supplies the satellite receivers. Testing and user experience has shown that this is vulnerable to fluctuations in supply voltage, but if you aren't using satellites connected direct to the Kbar then that's not an issue at all.

I did the same as you are talking about. I started with a Kbar and liked it so much that I ended up with several genuine Vbars. Today though things have moved on. IMHO if you aren't using the full 'Vcontrol' Mikado transmitter setup there are better options. Mikado after the Kbar experience became paranoid about being 'cloned' so they removed a lot of functionality such as Bluetooth support from the new Neo, along with any possibility for integration with 3rd party transmitters. My favourite at the moment is the Spirit Pro, the iKon2 or Brain2 (same thing) is another great option. Both of these give you far better functionality with 3rd party transmitters and better bang for buck.

As for the heli itself, there are a lot of great heli brands out there, a lot comes down to personal preference. I'm personally not a fan of plastic frame helis so Mikado arent on the top of my list but they do have a very strong following and they do fly great.

 

[k8idx]

Setting up the Kbar went okay until I got to the tail setup. The problem is that the tail pitch control arm only moves a very short distance. I looked at the mechanics and it all seems fine. In the setup program I had to move the sliders almost all the way to 40% but the instructions say it should be at least 80%. I'm using the shortest control horn on the servo and it's innermost hole to screw the ball into. How do I get this to work? It's not very clear whether you are supposed to change the endpoints in the TX or only use the sliders in the setup program. If the servo only moves a small portion of it full travel how can you get any resolution from the servo, any ideas?

 

[Smoggie]

If the servo arm itself isnt moving far then it may be that you have the servo type set wrongly. You need to make sure that the centre pulse width of the servo is set right, it's either 760us or 1520us. If you set a 1520us servo to 760us then the travel is greatly reduced.

Im kinda confused though.. if you arent getting enough travel then why are you moving the ball inward on the arm and reducing the throw in the software. that will only reduce travel even further?

You must not mess with tx endpoint.

 

[k8idx]

My description wasn't very clear. I'm getting TOO MUCH travel (deflection) of the servo arm. The tail pitch control arm only moves a few degrees from full pitch in one direction to full pitch in the other direction. The servo tries to move it TOO FAR so it binds at each extreme. There are two sliders in the setup program and the instruction says that the correct range is between 80% and 120% (I think it's 120) anyway I have to adjust them both to 40% or just a little more. The ball on the servo arm is only a millimeter or two from the servo shaft so I can't use a shorter servo arm, I'm using the shortest servo arm that came with the servo. So how do I set this up? It seems there is no way to get the sliders in the setup program anywhere near to 80%. The tail pitch mechanics are correct. The control arm only moves a very short distance, much less than the normal travel for the servo. I hope this makes more sense this time. When I built my 450 clone I had no trouble setting up the tail servo. Having the servo move such a short distance limits the resolution of the servo. It makes no sense to have it set up like this but that is how the tail mechanics are made with very short travel.

 

[Smoggie]

Sounds like you might have the tail mechanism assembled wrong. Can you take some photos?

 

[k8idx]

I didn't assemble the tail unit it was done at the factory. I also looked for errors but I can't see any other way the thing could have been assembled. I can take pictures though. I'll try to do that this evening. I have to admit that this really threw me when I saw how small the travel was in the tail pitch control arm. It just doesn't make any sense. I'll post a few pictures in a while.

 

[Smoggie]

There must be something assembled wrong. Hopefully the photos will make it clear.

 

[k8idx]

Okay here are some pretty poor photos of the tail mechanics. Most are from the bottom of the tail hardware because it sows the most relevant detail. The last two show the control arm at it's extreme of movement from one pitch extreme to the other. I've looked at this and I can't see how it could be assembled in any other way. Perhaps I'm just getting old. It sure doesn't allow for much resolution from the servo, and the vbar software doesn't like it either. Maybe you will see something I missed. I hope so anyway.
Thanks for your help, -Paul

 

[k8idx]

I forgot to add about the above pictures that the first three are of the pitch very close to zero. The last two are of the maximum pitch in each direction. I would have posted these sooner but I experienced a bit of Christmas interuptus.

 

[Smoggie]

The tail mechanism setup in those pictures looks fine. What about a photo of the servo arm end?

 

[k8idx]

I'll shoot and post pictures of the servo this evening when I get home.

 

[k8idx]

Well here is a picture of the tail servo with it set to it's center position. As you can see I'm using a short horn and I have the ball in the innermost hole. I'm beginning to think I should go through the entire setup procedure again and see what happens. The only thing that could shorten the throw of the tail pitch control arm would be a short shaft. It's possible that the gear I received in my kit was made incorrectly. I noticed that by moving the tail rotor outward just a few milometers makes a huge difference in the throw. Perhaps they drilled the divot where the set screw locks into on the shaft a tiny bit too far from the end of the shaft. That's all I can think of.

 

[Smoggie]

The photos looks ok. The ball should be further out on the servo arm but that would only increase the throw. Your suggestion that the 'dimple' on the shaft may be a couple on mm too far in makes sense.

 

[k8idx]

Yeah I've been thinking exactly what you said. I ordered a new tail gear/shaft and we'll see in 2 months when it gets here from china. Maybe it wont take that long but I'm not holding my breath. In addition to that I am beginning to think that the Kbar is faulty. One of the servo channels fails to initialize when the power is connected. It's always the same channel too. I power up everything and that servo acts like it has no power one it. Later I'll look at the signal with an oscilloscope. I can guess what I'll see, no pulse train from the kbar. I tested that servo in a different receiver and it works fine. It's not the servo so it almost has to be the kbar. That's what I get for buying a cheap part. If I tell the seller that it's bad they'll just tell me to drop dead. It's one of the perks of buying from china. I sure would like to fly this heli. Someday sooner or later I'll get it straightened out. I have to say that this is the most troublesome build I've ever experienced. I've probably built over 30 models over the years and I've never had problems like this. So I guess I'm going to do what I should have done in the first place and buy a Brain 2. I love the save feature. I've seen a video of it and it really works. It's pricey but I think it's worth it. Too bad the kbar is bad, I can't sell it. What a waste of money. Thanks for the help and I'll keep you posted.

 

[Smoggie]

You could grind a new dimple into the shaft?

Kbars are normally reliable but they are clones so you can never be 100% sure. One thing to try is if the servo doesn't initialise first time is to just powe cycle the heli by disconnecting and reconnecting the battery. If that fixes it then it's not the FBL it's just the power from the BEC not ramping up quick enough to initialise the servo, I've seen this occasionally.