eroc144

My Feedback: (1)

I crashed my .074 powered Pacer yesterday shortly after takeoff on my first flight of the evening. It was my first crash in a couple of years and for the record it was spectacular. I took a few laps around the field and as I exited the turn for the upfield leg the plane stopped responding to the transmitter and spiraled in. I've flown this plane a couple dozen times over the past few weeks at the same field with the same gear with no issues, but this time I connected a hextronik voltmeter directly to the receiver and I'm wondering if that might have killed my battery. When I connected the voltmeter pre-flight it read "perfect" but when I arrived at the crash site the voltmeter was flashing red (luckily the plane had split open so I was able to see it flashing red from a distance!)

So my freshly Accu-charged, 8 month old, 370mah NiMH battery with ~ 20 flights on it went from full charge to zip in under 10 minutes. On previous outings I was getting four 10 minute flights and the voltmeter displayed "good" afterwards. Has anyone had similar experiences with these voltmeters? Did I do something abjectly stupid by leaving the voltmeter connected? What's the best way for me to check the servos to see if any of them are shorting out?

EG

rainedave

My Feedback: (1)

Most r/c voltmeters apply a load on the pack in order to give a more accurate "real world" reading. I think it's usually between 150ma and 250ma depending on the make. Keeping a voltmeter attached would be like having two or three extra servos draining your pack.

David

gkamysz

My Feedback: (19)

Those simple on board voltage indicator require you to wiggle the stick vigorously for a few seconds to get an accurate reading, they do not have resistive loads. Without doing that you are just getting a resting voltage which doesn't indicate much of anything. The voltmeter itself draws only 20-30mA. Sounds like the pack just died.

I would cycle the pack to see what the capacity is. If you do not have a way to measure capacity, just replace it. After charging you could plug in each servo individually move it and see how the pack voltage responds. The best way would be to read the actual current draw of the servo with an ammeter.

Andrew

Man, EG, that's tough to hear - the Pacer is a great plane. Like David said, many voltmeters are "loaded". Can you give us the specs on the one you were using? It just depends on whether you were using a loaded meter or one designed to be connected the entire flight.

If you have a servo extension cable, you can snip one of the power wires, red or black, and use an ampmeter as a splice. Hook your servos up to the extenson and run them thru a series of cycles checking the current draw. Unlike voltage measuraments which can be taken at the terminals, your ampmeter will have to be in the circuit, unless it's a clampon. ServoCity has fairly complete specifications for Futaba and Hitec servos, including current drain.

Keep us posted on what you are able to find out.

eroc144

My Feedback: (1)

Here's a link to the [link=https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=2038]Hextronik Volt Meter[/link]. The site doesn't give specs, but the listing says low current draw and many of the posters / reviewers indicate they have this wired into their systems during flight. Then again, maybe they're using 2200+mah batteries...

I've got a very simple volt / amp / ohm meter and will see if I can splice it into the circuit and test the servos. Interesting specs on the ServoCity site - the HS65s I use draw 400ma whereas the HS55s only draw 150ma and HS81s draw 220ma. Wonder why the HS65s draw nearly twice as much when their torque lies between HS55 and HS81?

EG

gkamysz

My Feedback: (19)

HS-55 and 81 definitely draw more current than that. It's been a while since I've checked but stalled current is .5A for the HS-55. I think HS-814 was almost 1.0A.

Raymond LeFlyr

My Feedback: (2)

I have Voltwatch's from Tower hooked up to each of my larger models - and have since they first started advertising them. I check them after the range check prior to the first flight of the day - and after each fligh, before I turn off the system, I wiggle the right stick vigorously and watch the pretty lights blink. So far (knock on balsa), so good.

I did catch a bad pack maybe two years ago but darned if I can remember if it was at the field on or the bench. Anyway, the point is that I do use them and do depend on them.

I expect that they all come from China anyway and probably from the same factory - made by healthy, happy children. And probably there are bad ones produced now and then if the kid is day dreaming about Chairman Mao.

Toad

lol
I can almost see that "daydream". A chineese guy that moved out here after visiting Las Vegas.... He daydreams about Sheryl Crow. now I can relate to dem 12 yr olds over there doing that.

supagloo

Last spring I had a similar experience with a dead battery. This time it was a small glider that spiralled verticalli to the ground and crashed.
The battery was a square 4 cell pack of Sanyo Nimh AAA cells.
It turned out that the heat shrink wrap of the cells was not strong (or long) enough to prevent a short cut of 2 cells in this setup.

As the battery (the remaining 2 healthy cells!) was fully charged the voltage was high enough to power the receiver and servos so it looked as if nothing was wrong.


Now I wrap an extra layer of paper around each individual cell to avoid unwanted contact before shrinking them to a package.

g-rock

My Feedback: (1)

eroc144,

I have had nothing but bad luck with NiMh batteries. They often do not have a high enough discharge rate for my applications. I did some testing of NiMh batteries made in China when they first became available around 2002 and decided not to use them. Initiallly when LiPo's became available, they also had a very low discharge rate but look at them now.

I have switched over to LiPo's in all of my models and use a BEC type regulator if the model is not EP.
Gene

digital_trucker

I used a 350 NiMH pack in my Q-Tee (3 servos) and it performed just fine. My US-60 has a 1500 NiMH pack w/4 servos and does incredibly well (a voltwatch is on that one). My Herr Cloud Ranger has a HUGE 1000 NiMH pack for 5 servos and also does great (that pack was picked for weight, not capacity).

I did have a Voltwatch on my Q-Tee, and noticed that using HS-65's caused the indicators to dip into the red momentarily if I wiggled two or more servos at a time. I'm using a Spektrum DX7, so I picked up one of those little capacitor doodads for the Rx and that issue went away.

eroc144

My Feedback: (1)

Yes, mine does the same thing. Tell me more about the capacitors you added.

EG

digital_trucker

This is a whatsit that Spektrum sells. It's just a capacitor with a connector on it...plugs into an empty channel on your Rx and compensates for any momentary voltage drop. I can't seem to put my finger on a link just yet. I also see that Spektrum is offering LiPo Rx packs.....how interesting.

digital_trucker

I finally found the voltage protector for Spektrum radios...

http://www.horizonhobby.com/Products...ProdID=SPM1600

small_rcer

Looks like a single 10volt 4700uf cap to me. Should be able to get at local electronics distributor.

Jim H

flyinrog

My Feedback: (1)

Dang! I was always under the impression it was a no load,,no wonder I only get 2 or 3 flights out of my batts, I'm running my plane with the thing plugged in or per Dave 2 flights in one....the more you move the sticks the more lights light up so its a two fold drain, since lights drain more energy than motors!!??!!......Rog

gkamysz

My Feedback: (19)

NO! The on board voltage indicators do not draw any more current that it takes to drive the LED, about 20mA.

flyinrog

My Feedback: (1)

Ok, I bought my new radio yesterday and (futaba 2.4) I plan to put it in my Herr Extra,plugged the radio in my charger and then turned the switch on in the plane and the light was on the 2nd green light, it took roughly 24 hours for the battery to be completly drained by the voltwatch, mine are the hobbico version its a 600mAh battery since I have only the one rx for my 2.4 I plan to use it in the Extra this week,, will try my conquest to fly the big stick with, my other radio is only gonna be used for 2 channel flying I think...Rog

gkamysz

My Feedback: (19)

24 hours at ~20mA is 480mAh. About what we would expect.

2fast4u

My Feedback: (5)

I may be out of line, but I don't know what size plane you were flying there. The 350mAh pack is really small to begin with. When I was heavy into 1/2A I found the 350's to be too small for the most part. The only thing I ever trusted them on was 2ch planes running HS-55's. Anything above that should have a bigger battery IMHO.

If the 350 was used for it's light weight, then maybe a LiPo would be a better choice for you. Caution with the LiPo battery is that the internal connections are subject to vibration damage, so use lots of soft foam.

I hope you find the cause of the crash. Sorry it happened, but at least as you say, it was spectacular!!!

gkamysz

My Feedback: (19)

I used to fly a 2 channel speed 400 electric 13(?) years ago with 2 Futaba S-133's and a 50mAh pack. That's right, the ESC didn't have BEC. I found that wiggling the sticks continuously on the ground gave me 12 minutes of radio before it quit. I regularly flew 2, 5 minute flights with it. Some years later('99-'01) I flew F5D electric pylon racers at 150MPH with 2 servo's, maybe HS-65's, and 110mAh packs. Always peaked before flying that day and always peaked after several flights of 3 minutes (90 seconds at 150MPH and 90 seconds gliding). I never saw more than 12mAh put back into the pack after several flights. I've often used what people consider to to be extremely small packs. If you choose to do this you have to be very aware of how much actual capacity is available and you have to be aware of the condition of the battery. I wouldn't recommend it for everyone. When space and weight allow I go big on batteries and never, ever, use Chinese cells for radio power.

combatpigg

My Feedback: (3)

After a few thousand minutes worth of RC combat [ usually with a pair of HS 81s], I've found that 300 mah packs are good for 3 ten minute rounds plus the time it takes to retrieve the planes, gas them back up and open another beer. The new high frequency systems [2.4 gig] suck so much juice that they drain the same set up after just a flight or 2.

digital_trucker

I run a 370 NiMh pack in my Q-Tee, Spektrum 2.4 radio w/ 3 HS-65 servos. Considering that it's powered by a Wasp off a 2oz tank, I can get 20-minute flights easily. Usually I limit the flights to around 10 minutes, and I can get 3-4 flights before I start thinking about recharging (I have a voltwatch on it, too). Basically I can figure on 40-60 minutes of flight time between charges.

mylamo

My Feedback: (1)

My this is bad news. For years I flew small planes with
two and three channels mostly pretty fast rigs with mini
servos,Cannon and Airtronics with 110 mah nicads. Three
flights easy. No problems

flyinrog

My Feedback: (1)

I use mostly 270-350 mAh in my 1/2a stuff? , My Herr extra has the permanent voltwatch on a 600mAh battery and only is good for a couple of flights...so I drained and recharged it and just bought a micro switch from radio shack to cut the voltwatch off during the flight (really hard to see it then) and can turn it on and check it after each flight....Rog