stat71
Flying officer
Posts: 7
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Post by stat71 on May 6, 2010 7:09:55 GMT 1
Hey there,
My first post here - looks like a great community!
Recently purchased a SC and following a LiPo conversion was up and flying. A couple of small "crashes" later I was receiving no response throttle TX to engine.
I checked LiPo volts and all connections - rudder / elevator servo's still operable but no throttle.
Next step I bypassed the Rx / ESC and connected LiPO to engine direct - no problem it fired up straight away.
So - I seem to have a problem which is related to some part of the Rx / ESC unit.
Some questions:
1. Is my summation and conclusion of the problem above correct?
2. I know I can replace the receiver / esc, but is this the best course of action?
I'm looking for some learned advice and suggestions, so thanks in anticipation!
Scott
Sydney, Australia
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vroom
Flying officer
Posts: 30
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Post by vroom on May 6, 2010 8:11:58 GMT 1
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stat71
Flying officer
Posts: 7
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Post by stat71 on May 6, 2010 9:53:03 GMT 1
Thanks for the reply...
Re: upgrade path - I though this might be the route of choice.
Is there a suitable Rx / Tx that is available at hobbyking to combine with the suggested ESC / Servo's??? Reason I ask - I'm in Australia and to date have used hobbyking almost exclusively.
Also - Should I also consider going brushless if I'm going to being upgrading the electronics? If so, any suggestions?
Regards
Scott
Sydney, Australia
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vroom
Flying officer
Posts: 30
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Post by vroom on May 6, 2010 20:12:41 GMT 1
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stat71
Flying officer
Posts: 7
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Post by stat71 on May 6, 2010 23:05:13 GMT 1
Thanks vroom - I like the sound of a motor upgrade - the only thing I'm a little confused over is the difference between an in-runner and out-runner, and any advantages / disadvantages?
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vroom
Flying officer
Posts: 30
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Post by vroom on May 6, 2010 23:51:53 GMT 1
Im fairly new to brushless motors myself so Im not sure of ALL the advantages and disadvantages of the 2 different types of motors. I do know that an inrunner motor has to use a gearbox though and an outrunner doesn't need one. Thats why I personally prefer outrunners.
The other difference between the 2 motors is an inrunner spins the shaft inside the motor housing and an outrunner spins the motor housing and the shaft together.
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Post by ginginho on May 7, 2010 9:51:16 GMT 1
Oh dear. I think you'll get Fly on here stating the short-falls of the TP motors (bendy shafts, poor build quality etc).
You should check out other threads that discuss brushless upgrades, you'll find a lot of useful information in those.
Scott, as for your JR radio, it's a shame it isn't a modular type, as you could have dropped in a 2.4Ghz module from another manufacturer (e.g. Assan, FrSky). There is a thread on rcgroups.com that discusses fitting a module under the covers of radios similar to yours. Although as it's only a 4 channel it's questionable whether it would be worth it.
Inrunner vs outrunner: inrunners tend to be high revving, hence why you'd need a gearbox on the SC. The magnets rotate with the shaft within a "cage" of the wiring. Outrunners tend to have a lower Kv, and tend to be a bit more efficient. The magnets rotate around the outside of the wiring.
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Post by flydiver on May 8, 2010 2:32:18 GMT 1
Maybe that warning was enough. I'm getting tired of trying to warn people off cheap stuff. Let 'em learn the hard way. You would maybe think their problems with the cheap Cub electrics might ring a bell but doesn't seem to.
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vroom
Flying officer
Posts: 30
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Post by vroom on May 8, 2010 4:07:35 GMT 1
Well maybe you could make a better recommendation from Hobby King for him? I bought 5 of the TP motors almost a year ago. I finally killed one the other day in a crash that turned the whole front end of my plane its a puzzle (I hate puzzles!) but ran very good for the year I used it. The others are all still in perfect working order and are used regularly. I wouldn't recommend a motor that I didn't use myself. Plus heard from many people that use and like them too.
I would much rather toast a $8 motor in a bad crash vs a $30-$40+ motor. Now, once you stop crashing... then maybe get better quality motors.
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Post by ginginho on May 8, 2010 9:17:08 GMT 1
Ok, well to really be able to advice properly, there are some things that we'd need to know, such as the budget, required flying characteristics and future plans (i.e. more airframes) that Scott has. The radio you suggested is OK but it'll be a pain if Scott is planning on have multiple planes as he'd need to remember and set up and throws/servos reversal/DR&Expo each time he wants to fly a different plane. So if he is planning on getting more than one, a radio with model memory would save a lot of grief. As stated before, there are lots of possible motors listed in other threads on here, it seems pointless listing them all again. Basic requirements for a suitable motor for the SC are:
1) Power: 100 - 140W for similar to stock performance. 180-200W for a reasonable performance enhancement. ~250W for high performance, capable of vertical.
2) Kv: ~1000Kv to spin up to a 10" prop, 1100Kv for a slightly smaller prop and so on. It's not worth getting one with a rating over about 1200Kv as the SC will not look right with a 7" prop.
3) Amp rating: Should be higher in normal running than the expected pull with a prop that suits. Therefore for 200W (in) the motor would need to handle ~20A (P=V x A, Safe assumption is on a 3S that the input voltage drops to 10V under load).
Consideration is also required for the way the motor mounts, either in front of or behind the firewall. A mount to suit this will be necessary.
A suitable ESC and servos will also need to be budgeted for, along with a radio set if the JR 4 channel isn't used. I've not used the SS ESC, but have heard that they can be temperamental with some motors due to having very limited programming capabilities.
Best advice I can give to Scott is to have a read of some of the other threads on here. Dillz's (long and winding ;D) "My new Cub" thread in the Building section covers a large amount of what you'll need to know or consider. A fellow countryman of yours too.
Oh, and BTW...Don't be fooled that because the SC is a relatively cheap way of getting into RC planes, that it's a cheap hobby. It is not.
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Post by flydiver on May 8, 2010 15:39:08 GMT 1
I would much rather toast a $8 motor in a bad crash vs a $30-$40+ motor. Now, once you stop crashing... then maybe get better quality motors. Ever had to replace bent shafts on those? They bend VERY easily. You don't need a crash, a decent prop strike will do it when long like you need to use it in the Cub. I've personally had about a 10% DOA incidence with them. Other folks seem to have similar luck. The super simple series of ESC seem to be of the same quality along with the TP ESC. If they work, you're good. If they don't it is extremely frustrating and confusing, even more so for the newbie that has no trouble shooting skills at all yet. The number of threads of 'I got this TP motor/Mag8/SS from HK and it doesn't work...." is positively rampant. In a way the newbie is even better off with a slightly higher grade of equipment to start so they don't have to always be wondering what the hell is wrong with it. I've been down the path. After you have a few planes fall out of the sky because you cheaped out on small components you begin to realize that it's poor economy. Yes, you need to get to the stage where YOU aren't the failure point anymore so you know. But newbies benefit from better gear by not having to constantly screw with it. There are LOTS of suggestions in the forum and very complete discussions of what to do and why to do it. If you don't have the patience to read and learn, then you learn the other way. It's a longer path strewn with foam parts. |
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stat71
Flying officer
Posts: 7
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Post by stat71 on May 9, 2010 0:04:11 GMT 1
Thanks for the replies and questions ginginho, vroom and flydiver.
My budget is open - but as I am still a novice and only currently using a SC, I don't want to spend a small fortune. My plans atm are:
- Use the JR Rx / Tx
- I purchased x2 HS 55 servo's yesterday and a brushed ESC
- Upgrade to a brushless inrunner (Hobbyco?)
I've installed and have now had a quick flight with the new electronics - no problems and was impressed with the end result.
I've spent the last 72hrs reading widely on the topics of ESC/BEC, motors and the SC in general. I now have a basic understanding of each of the area's and plan to build my knowledge with further reading and application.
Am heading over to Dillz's thread now for a read (coffee is ready!)
Thanks again
Scott
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Post by flydiver on May 9, 2010 4:45:37 GMT 1
Fine purchases and decent decisions. The Quattro is functionally as good as the DX5e without being caught up in the Spectrum proprietary trap. It also suffers from the same limitation having no model memory but that's not an issue right now. HS-55 are fine servos and more electrically efficient (almost 2x as good) as the Hextronic 9gm. This is good as almost for certain the brushed ESC has a low amp BEC, most do.
You'll want to check that inrunner temperature after flying hard for a minute. Or do a 30 second (ONLY) full throttle bench test (strap the plane down WELL!). If the motor is cool or merely warm after that you are propped OK. If it is too hot to touch you have too large a prop and the motor may burn out. Inrunner's have a specific KV, and you need to gear them to match a specific prop size to not over tax them. You can't assume just because you put a similar looking motor in the Cub gearbox that it uses the Cub prop. Same idea for out runners but you don't have the gearing issue.
Check the ESC too. No electric device should ever get too hot to touch and hold. If it does you have a failure brewing.
Do not to an extended bench test. That's a shortcut to burned up parts due to lack of air cooling.
Be aware that the LVC on the brushed ESC will probably not be safe for lipos. Most are not. If you fly to LVC you'll wreck your lipo. The Cub ESC is not a quality unit and the LVC could have been better but at least it was serviceable.
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stat71
Flying officer
Posts: 7
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Post by stat71 on May 10, 2010 1:25:54 GMT 1
You'll want to check that inrunner temperature after flying hard for a minute. Or do a 30 second (ONLY) full throttle bench test (strap the plane down WELL!). If the motor is cool or merely warm after that you are propped OK. If it is too hot to touch you have too large a prop and the motor may burn out. Inrunner's have a specific KV, and you need to gear them to match a specific prop size to not over tax them. You can't assume just because you put a similar looking motor in the Cub gearbox that it uses the Cub prop. Same idea for out runners but you don't have the gearing issue. Thanks flydiver...I did as you suggested and gave the brushed motor a 30sec "foot to the floor" on the bench - a wisp of smoke could be seen climbing from inside the cowl, it stunk and was very hot. So I've been using the stock prop (9x6) and following some reading think the most appropriate action would be to buy some GWS 10x6 direct drive props (correct me if I'm wrong on this). Check the ESC too. No electric device should ever get too hot to touch and hold. If it does you have a failure brewing. Did as suggested and the esc remained "luke warm" only. Be aware that the LVC on the brushed ESC will probably not be safe for lipos. Most are not. If you fly to LVC you'll wreck your lipo. The Cub ESC is not a quality unit and the LVC could have been better but at least it was serviceable. I checked the residual V's in the LiPO after the LVC kicked in, was reading around 2.9 to 3.1V per cell = about 9V, is this ok? Cheers Scott |
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Post by flydiver on May 10, 2010 2:32:16 GMT 1
Stock gearing is something like 3:1 > meaning the motor goes around 3x for every revolution of the prop. ALL electric motors have a fairly narrow operating band. Too small a prop you don't get much, kind of like driving around in your car in 1st gear. Too much prop is like trying to pull a large trailer with a VW bug > seriously overloads it. Heat and smoke means you've overloaded it. You'll notice a motor spec is [KV=revolutions in thousands/volt]. So a 1000KV motor given 10v will go 10,000RPM UNLOADED (no prop). Put on a tiny prop and it won't slow down much. Put on too big a prop and it will slow down a LOT and get hot. The conventional goal is about 80% of unloaded RPM. ParkZone doesn't tell us what the stock motor is, but something like 2400kv is kinda reasonable. So, geared 3:1 means the prop is turning 2400/3 = 800 effective KV. They've figured out for THAT motor that the 9x6 prop with a 12v lipo is a reasonable work load. The motor you got is likely much higher KV so is trying to turn the prop MUCH faster than the motor can handle. You need to prop DOWN until the motor only gets warm. The stock 9x6 and the GWS 10x6 are pretty similar in terms of amp draw. Do you have specs for that motor? Specifically, KV, max and cont. amps? For a much better education on this study the gear charts at GWS for this 400 motor (this is NOT the Cub motor) and look how the prop suggestion changes with voltage and gearing. www.gwsus.com/english/product/powersystem/eps400c.htmSo, you need to prop for THAT motor and just because the Cub used a 10x8 on NiMH and a 9x6 on lipo has nothing to do with what your new motor needs. You prop to the motor and the voltage. The actual plane is less important. Sounds like the ESC should be OK. LVC - NO, NO, NO. 9v RESTING after you have flow is too low. You want to see about 3.5-3.7v/cell RESTING. The 3v/cell you see references to are LOADED (under power) voltage which will be lower than resting voltage. You need to whack a couple minutes off your flying time once you get it propped right. Power draw will not be optimal as long as it is over/under propped. Do some reading in this thread. www.rcgroups.com/forums/showthread.php?t=1136470And you may run across references to a wattmeter. This is one of the best tools (after a good charger) you can have in your electric toolbox. More info here. www.rcgroups.com/forums/showthread.php?t=311574There's sure a mess to learn, eh? |
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