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Post by NorCalAirman on Apr 24, 2011 0:31:46 GMT 1
Well, this is my maiden report after upgrading to brushless. Despite having the torque angle all wrong, she was flying great and had PLENTY of power. The new CT6B radio was nice too. Well, I was just flying along level when suddenly the servos started twitching. Next, they stopped responding my cub headed off into the blue yonder. I cut power and thankfully she responded, but still no servo control. Came in at about a 45 degree angle, prop split in two, mount shattered, battery box torn out. Time to rebuild.  |
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Post by NorCalAirman on Apr 24, 2011 3:54:04 GMT 1
So I plugged the battery back in after getting home to see if anything still worked. Lo and behold, it did. The servos were fine, the motor seemed fine (bent shaft of course), everything seemed okay. Then the servos started freaking out and the motor started randomly twitching. Could it be a bad receiver? What could cause it to do that?
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Post by killioughtta on Apr 24, 2011 5:42:09 GMT 1
Sounds a lot like a brown-out. Search the SCC for 'brown out' and read up. You'll need either an ESC that can handle more amps or a UBEC of around 5 amps.
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bloodboughtchad
Flight lieutenant
Super Cub LP... Packing Tape... Glue... Fingers Crossed & Ready for Fun!
Posts: 55
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Post by bloodboughtchad on Apr 24, 2011 14:11:18 GMT 1
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Post by flydiver on Apr 24, 2011 15:52:18 GMT 1
List all gear used again - be SPECIFIC, it's important.
Links if you got them too.
Initially sounds like and ESC problem. These can be hard to sort out, especially postmortem. What failed before it went down and how do you sort that out from the broken parts?
Did you do a range check?
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Post by NorCalAirman on Apr 24, 2011 16:44:31 GMT 1
Exceed RC Alpha 480 brushless motor
Exceed RC Proton 30A ESC
2x T-Pro SG90 servos
FlySky 6ch RX
Ground test was fine, practically jumped off the ground at takeoff. I was flying for about five minutes with zero problems when it started freaking out. The ESC got mangled in the crash, so it is getting replaced regardless. I might jusat do that, add a UBEC, then see where I stand.
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Post by flydiver on Apr 24, 2011 17:12:08 GMT 1
This was NOT a full aileron, 4 servo conversion? That ESC appears to be a 30A HobbyWing, linear 2A BEC. If all it had to handle was 2 servos it should have been fine. Not good if it was dealing with 4 servos. The HXT 900 and T-Pro 9g servos work well but are a bit power hungry. You propped a 10x6-right? Did you wattmeter it? An option would be to go to a larger ESC with a 3A switchmode BEC. www.headsuprc.com/servlet/the-1606/Emax-35-Amp-ESC/DetailThose will handle 4-servos OK. If you are really paranoid than put in a secondary BEC. The Exceed 40A posted at Hobbypartz says it's a 3A linear BEC. I just bought one a couple months ago specifically because it had a switchmode BEC. Not sure if that's an error or I now should be concerned. Can't comment on the TX/RX with this one. I have not familiarity with the product. If it passed a good range test it should have been OK. I assume short antennas so having the signal shielded behind motor/battery/etc. and loss of contact could be an issue. Since it seems to be doing this on the bench you may be able to sort it out by replacing suspicious parts > ESC and RX seem the most likely. |
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Post by NorCalAirman on Apr 24, 2011 22:49:03 GMT 1
No ailerons yet, which is why I didn't connect the UBEC.
It was using a GWS 10x6 prop, I did not wattmeter it as I don't own a meter.
If I'm going to wire up the UBEC, do I need to go up in my ESC selection to a 40A?
I seriously doubt it was interference as it was running great, then suddenly went spastic while in level flight. Then the exact same thing happened while it was on the ground. I cut open the ESC and nothing is obviously fried or shorted. All damage looks to be from the impact.
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Post by flydiver on Apr 25, 2011 0:45:16 GMT 1
Increasing the amp rating won't hurt anything but weight and your pocketbook. OTOH, that should have been enough. Since it's damaged it's hard to tell what was the cause. Having it go spastic while sitting indicates something wrong, but what?.
Suggest you remove all electronics, hook them up, spread them out as well as possible to avoid interference, and see what you get. I had a Stryker that couldn't get 20 feet of range and it turned out to simply be the antenna strung along the LONG servo lead. Once re-routed it was fine. This was 27MHz too. 2.4GHz should be more resistant to those problems.
A UBEC or new ESC will not save you if it is the RX or TX. You need to go through a process of trial and error by elimination and replacement.
This is where having redundant electronics can be really useful as you can isolate single parts and see what results you get.
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Post by NorCalAirman on Apr 25, 2011 1:41:11 GMT 1
Could dying TX batteries cause this? I plugged my TX into the computer to play with FMS and after a minute it stopped working. I'm colorblind, so I can't tell what the LED on the TX is trying to tell me. The batteries are not new, but not sure how old.
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Post by flydiver on Apr 25, 2011 3:16:35 GMT 1
Absolutely! It's actually consistent with your symptoms.
Batteries recover a bit when not used so the voltage bounces back up but rapidly declines again when loaded.
Alkaline or re-chargeable?
Put new ones in (or charge) and see if the problem goes away .
No voltage read-out? Single LED?
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Post by NorCalAirman on Apr 25, 2011 4:01:41 GMT 1
Alkalines, single LED, which has three colors I can't differentiate. So low batteries in the TX could result in twitching servos? God, that means I did everything right and just forgot to switch the batteries. I'm going to go punch myself in the face, then start working on a motor mount with a proper torque angle.
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Post by flydiver on Apr 25, 2011 5:08:04 GMT 1
The RX has no brains. It just sends info from the TX onto the components. Remove that but apply power and it's can be a bit like a chicken with it's head cut off. Behavior depends very much on the specific components.
Protocol - TX on > power to system/plug in battery
Done flying - remove battery, turn off TX.
Always do it that way. Any other way is poor and field habit and can get you in trouble with other fliers.
Spektrum folks may never learn this or get sloppy because that system generally doesn't act weird if plugged in without a signal. That doesn't make it right and it IS becoming evident that Spektrum, under certain circumstances, can interfere with other fliers.
72MHz often goes nuts. I don't know about other systems.
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Post by NorCalAirman on Apr 25, 2011 11:52:13 GMT 1
TX on > batt plug in and vice versa is once thing I'm trying to stress to my flying buddy, but I've been pretty diligent. Even though I have never flown with anyone but him, I try to maintain good habits.
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Post by toff on Apr 25, 2011 19:42:24 GMT 1
Protocol - TX on > power to system/plug in battery Spektrum folks may never learn this or get sloppy because that system generally doesn't act weird if plugged in without a signal. I'm going to take umbrage with this quote! ;D Wrong, wrong ,wrong.  Using my dx6i, and ar6100 rx's, if I switch off power to the TX, any plane will generally start to do the funky chicken, including motor powering up to full throttle. also happens with my ar600 and 500.  Power off on plane first then TX. Power on on TX then Plane. ALWAYS! |
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