|Dec 16, 2005, 06:39 PM|
For Those of You Who Use Lipos in Your Planes
Iíve been looking for some new batteries for my Superfly-E (EPP delta flying wing) (here). I was originally intending on getting Nimhs (for the reasons said in that thread), but it appears I can get some lipos for pretty cheap.
One of the major concerns/drawbacks/queries about using lipos on a plane is when to stop flying.
I have quite a few lipos; I think itís about 9 packs, which I use, mainly on my helis, but also in a micro RC car. They are fine, for the heli, I have a LED and buzzer alarm (from www.customideas.com), and for the car I just have a little LED poking out the back. I never take both that far away, so I can stop flying/driving pretty much as soon as I need to.
But with planes, buzzers and LEDs would be kinda useless as far as I can see, as you fly them much further away. It seems that most people do it by when the plane noticeably starts to lack power, but if itís my first ever flight with the plane, how will I know?
I know I can get lipo ESCs that have a soft/hard cut-off, but being 15 I donít want to spend too much on what will essentially be a chuck around plane. Of course, if they are real cheap, I may be interestedÖ
At the moment I just have a GWS ICS 300, and a GWS 350, with a C g/b I thinkÖ
Any input would be appreciated,
|Dec 16, 2005, 06:46 PM|
Northern Ireland, UK
Joined May 2004
If you dont want to spend a lot of money but are willing to spend a bit of time building, there are several projects listed in the electronics forum for LiPo circuits. Shouldnt cost more than a few £'s
One of which is http://www.rcgroups.com/forums/showthread.php?t=264289
If you aren't 100% sure about schematics, post a message and ask.. alternatively maybe a teacher at your school could help.
|Dec 16, 2005, 07:17 PM|
Run your plane in your hand a few times you will get a good idea how long it will last on your LiPO's but the one thing that you have with fixed wing that you don't have with heli's are the fixed wings..!! Plane ESC's cut only the motor but leave your other control surfaces under your control. You can stop flying early and land or just let the motor cut out and glider her in.
|Dec 16, 2005, 08:08 PM|
Hey Duane, do you have a wattmeter? Or even a multimeter? You can check the current draw at full throttle and half throttle and then calculate a rough approximation of how long your battery will last. Or you can fly around for a couple of minutes, land and then check the voltage drop at full throtle. It'll give you some good approximations.
I fiddle around with electronics, and I know that you can get free IC (integrated chip) samples from Texas Instruments. I've received free samples of op amps from them, and I'm pretty sure the voltage comparator used in the circuit above can be had for free too. Not sure if they ship overseas, but it's worth a try. All you have to do is go to ti.com, register, view the IC you want, then find the link on the page about getting free samples.
If I get some free samples and build the circuit, I'll send you one...not too much of a problem.
|Dec 17, 2005, 01:15 AM|
You can work out the current draw by looking it up on the GWSweb site (under power systems) - I think it's about 8amps for the GWS 300 motor on the superfly (but it depends which prop you use)
Then calculate the number of minutes that will give you (7.5 minutes for a 1000mAh battery, 15 minutes for a 2000mAh battery). Use a countdown timer to give you an alarm when it's time to land (I used to use my watch, others use kitchen timers).
You can subtract a minute or two (or not fly WOT all the time) for a safety margin.
Alternately, GWS now sell brushed speed controlls with lipo cut offs.
Or upgrade to a brushless motor and lipo friendly ESC :-)
motor and ESC for £27
|Dec 17, 2005, 08:21 AM|
|Dec 19, 2005, 01:39 PM|
I agree with Silent.
I have the GWS-400Li ESC which auto detects the number of cells you are running and sets the cutoff voltage accordingly.
The thing that is nice, once the battery reaches the cutoff voltage moving the throttle to 0% and back will give you throttle control back. After the initial cutoff just come in for a nice controlled powered landing.
Once you have an idea of how many amps your setup is drawing, a timer is a very good idea.
|Dec 19, 2005, 03:09 PM|
> Get a GWS-300Li. It costs $12.25 USD.. So thats like 6 pounds
You'd have thought so, but you haven't reckoned with UK prices!
ICS-300 Speed Controller 5-8 cells BEC £16.99
And that's the non-lipo version...
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