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Mikado V-BAR Mikado V-Stabi/V-BAR Flybarless System Software and Hardware Support


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Old 11-16-2014, 01:42 PM   #1 (permalink)
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Default Low Voltage of 3.3V Rail

I recently built a new Goblin 500 with the mini v-bar and the HobbyWing Platinum 100 V3 ESC. It flies great, but there are a few entries in the v-bar log that are kind of bothering me. One was about antenna switched so I reoriented the satellites. But this one makes me wonder if the BEC is up to the task:

Low Voltage of 3.3V Rail

I'm using the BK servos at 6V, but the ESC can do 7.4 or 8.4 as well. The specs make it sound like it should handle a high current load and it has the extra supply voltage wire too.

Anything I should try -- is it in danger of resetting during flight?
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Old 11-16-2014, 02:34 PM   #2 (permalink)
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i had the same thing!!! just us a cap and all is good!!! the bk servos are power hungry !!!!
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Old 11-16-2014, 02:59 PM   #3 (permalink)
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Thanks man... any idea what size cap to use...er microfarads. Would Fry's have it?

Also as far as wiring it up, would I wire it inline to the BEC voltage wire.
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Old 11-16-2014, 08:05 PM   #4 (permalink)
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here is the like http://www.vstabi.info/en/node/1422

or do a search here and you will get more info.

i had the same problem with power hungry servos used a cap and all good or the mikado YGE esc works great ( they have the cap built in from yge )
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Old 11-17-2014, 08:03 AM   #5 (permalink)
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I had to use a 6800uF cap on my 450 to eliminate issues, including warnings in the log. Just for context.

I tried 2200, 4400 (I think, maybe 4600?), and settled on 6800. A 10V rating should be sufficient; you can go higher voltage if you want, the caps will just get bigger for the same capacitance.

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Old 11-17-2014, 08:52 PM   #6 (permalink)
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So, are those that use the capacitor just hooking them up to a short servo connector and plugging into a spare port? I was looking for a Hitec PAD, as they send them with each HV servo, but I thought they had a little more to them than just a capacitor... I have two sets of RJX servos, but they brown out the Vbar everytime I test pitch pumps on the bench!
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Old 11-17-2014, 09:05 PM   #7 (permalink)
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I had to use a Y-cable (use a heavy-duty one), but yes. If you can plug the cap directly into a VBar port, that's ideal. You want it as close to the load (servos), and the voltage supply (BEC cable) as possible.

I'd prefer to have the cap plugged directly to the VBar, as opposed to plugged into a free port on an RX, for instance. If plugged into the RX, you have more servo plugs between the cap and the load.

Now whether that difference (plugged into VBar vs RX) is actually meaningful, I couldn't say.

Interesting, I'd never heard of the Hitec PAD before.
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Old 11-17-2014, 09:10 PM   #8 (permalink)
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Hitec Rep at my field... Here is their service bulletin.

June 2014: Brushless Servo Service Bulletin
While compatible with most radio control devices, the regenerative braking feature of the HSB-9XXX series servos may cause a problem if the device cannot accept a backflow of current. The types of devices that cannot accept this backflow are: Voltage Regulators, Power Safe Receivers and certain BEC circuits whether stand alone or integrated within an Electronic Speed Control. Check with the manufacturer or the Hitec website for a list of compatible models. If your device cannot accept a current backflow, then you must install a PAD (Power Absorbing Device - Hitec PN# 55756) as described in this manual. A PAD is included with every Hitec brushless servo.
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Old 11-18-2014, 12:33 AM   #9 (permalink)
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The Y-cable is a good idea. I wasn't able to find the right cap at Fry's today -- seemed like their stock was kind of low. I took my servo extension wire coming out of the v-bar that connects to the ESC RX supply lead and cut red and black to solder in the cap. Works fine.

It's only a 2200UF at 25V, but the 6800UF 25V they did have is too big. I'm thinking I'll order the 10V 6800UF cap on eBay since Fry's selection is so limited. Gonna try it with the smaller cap first to see if the voltage rail messages still appear.
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Old 11-18-2014, 02:56 AM   #10 (permalink)
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I am using this capacitor from Spektrum along with Talon 90 ESC on both of my Goblin 500s with no issues whatsoever. Pluged in RX-C port and ESC is plugged into RX-B.

NB! Never plug into RX A.

One of my Goblins was sold recently and I know it still fine.
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Old 11-18-2014, 06:00 PM   #11 (permalink)
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mcarter76, Digikey.com is also a good source for caps and similar items. Shipping was quite reasonable as I recall from ordering mine last year.

Ideally, you want low-ESR caps, from what I've read. I've heard Panasonic as a suggestion for a good brand.

As I recall, the size of my 10V 6800uF is the same as the size of my 35V 2200uF from Radio Shack. So the lower voltage rating definitely helps keep the size and weight down.
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Old 11-21-2014, 02:11 PM   #12 (permalink)
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Are the the capacitors that others are using from Digi-Key? they are only 8.8 grams, but they are larger than I expected!!!

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Old 11-21-2014, 02:56 PM   #13 (permalink)
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My caps are rated to 10V. The higher the voltage rating, the larger they are. I'm using 10V 6800.

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Old 11-21-2014, 02:59 PM   #14 (permalink)
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Quote:
Originally Posted by RedOctobyr View Post
My caps are rated to 10V. The higher the voltage rating, the larger they are. I'm using 10V 6800.

Sent using Tapatalk.
Hmm, I couldn't find any 10V when I looked (I am sure I just missed them...), but I am going to give these a shot (I bought a few)!!!
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Old 11-22-2014, 02:47 PM   #15 (permalink)
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Did 3 flights today with the 25V 2200UF cap and no more messages in log about low voltage of rail. Thinking I will try a 10V version though to keep the size/weight down.
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