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Old Jul 26, 2009, 11:23 AM
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Eddie P's Avatar
United States, NV, Reno
Joined Mar 2000
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Quote:
Originally Posted by Ron101
... I know the old school thinking but Tam has me convinced the spark just doesn't need a bigger pack... and this pack is feather light

but everyone has to run what makes them feel safe..

later
Ron
Like I mentioned, I was just making an observation, not a directive, ha ha. The "old school thinking" is to run a huge pack based on capacity and never re charging for two weeks or having head room to mis charge based on old school crap battery chargers. I'm not talking about that.

I'm talking about packs that can repeadedly absorb momentary amp spikes without eventual voltage sags that, in fact, can very well happen with a jammed flight control (s). Flight controls can often partially jam under positive and negative rapid onset G loadings in turbulence or aggrivated jerky flight maneuvering - or if the airplane has been sat in the sun for a long time and materials expand (closing in fine gaps between flight control surfaces) or if the airplane was not set up optimally, of there is a servo that suddenly starts to fight a flight control limit or a servo starts to buzz or hangs up. Also, when voltage remains optimal under load, the servos respond more crisply and accurately, meaning more positive flight control that does not "feel soggy" at speed or heavy maneuvering. That's all I'm saying.

Sounds like you are pretty comfortable with yours, well done, and that's just fine by me!
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Old Jul 26, 2009, 12:03 PM
Watt me worry?
Madmax1965's Avatar
Florida
Joined Mar 2006
3,862 Posts
Install A-123s and don't worry.
Two way to go ....either use the 1100mah pack or the larger 2300mah pack. Both packs can be charged through a deans plug @ 10 amps. The 1100mah pack is a 30-50 discharge and 6.6 volts. The larger 2300mah pack is 30-50 c discharge and 7.3 volts. I can fly all day on these packs but I usually tap them off during the flying secession. Tanic builds nice A-123 packs....the cells are welded so no high heat to the batteries during construction of the packs.
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Old Jul 26, 2009, 01:11 PM
Xtreme Power Systems
Lake Havasu, AZ
Joined Jun 2005
15,764 Posts
Typically, you only use a few hundred milliamps during a flight. Capacity and current capability are two different things and this is where people get confused. There are those that figure if they are using a really big pack that there will be sufficient power - that is not always correct. There are also those that believe sine they are only using a few hundred milliamps of current per flight that the current draw can't be very high - that is usually incorrect.

Even though you may only use a few hundred milliamps during a flight, you could still be seeing 10A surges, but for just milliseconds. With non-computer based receivers, this was not a big deal as this resulted only in a worst case of a "glitch", but usually went un-noticed. With computer based systems, a current draw exceeding what the cells can delivery results in a voltage drop. When this drop is tool much, the receiver will reboot. During this time, there is no control. When the receiver comes back online it may be told to continue to do the last thing that caused the reboot and it happens again.

We use A123 cells in all of our aircraft. My Spark is getting two 1100mAh, one to each end of the receiver's servo "bus". No switches too, as they are the number 2 source of power system failures (with batteries being number 1).
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Old Jul 26, 2009, 01:20 PM
Watt me worry?
Madmax1965's Avatar
Florida
Joined Mar 2006
3,862 Posts
A-123s are great. I have a 6s2p pack in my Sebart Sukohi to power a Hacker 50-16 L motor. I have had this pack in my Sukohi now for 3 seasons and I have never removed the pack from the plane. I have a charge jack on the side of the plane and I plug in my Mastech 5020 lab charger and zap the pack @ 20amps....full charge in less than 10 minutes and I fly for 8 minutes. I also tap off my onboard pack using the Mastech. Too bad the cells are only 2300mah because I would love to use them in an EDF to power the motor but I would need to use too many for 4600mah and the weigh is the problem..
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Old Jul 26, 2009, 03:22 PM
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Eddie P's Avatar
United States, NV, Reno
Joined Mar 2000
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Quote:
Originally Posted by JimDrew
Typically, you only use a few hundred milliamps during a flight. Capacity and current capability are two different things and this is where people get confused. There are those that figure if they are using a really big pack that there will be sufficient power - that is not always correct. There are also those that believe sine they are only using a few hundred milliamps of current per flight that the current draw can't be very high - that is usually incorrect.

Even though you may only use a few hundred milliamps during a flight, you could still be seeing 10A surges, but for just milliseconds. With non-computer based receivers, this was not a big deal as this resulted only in a worst case of a "glitch", but usually went un-noticed. With computer based systems, a current draw exceeding what the cells can delivery results in a voltage drop. When this drop is tool much, the receiver will reboot. During this time, there is no control. When the receiver comes back online it may be told to continue to do the last thing that caused the reboot and it happens again.

We use A123 cells in all of our aircraft. My Spark is getting two 1100mAh, one to each end of the receiver's servo "bus". No switches too, as they are the number 2 source of power system failures (with batteries being number 1).
Well said Jim. I don't want anyone to think I'm ramming ideas down throats here! This is a good discussion though; all this talk about RX batteries, size, etc. is very salient as we see bigger and or faster EDF's these days. I think the majority of people's early teething problems with 2.4 on big jets (those were turbines leading the way for the most part), are probably more RX power supply related than not. The best point you brought up that I took for granted was the point of amp capability NOT simply being dependant on large pack capacity. And that's why I also really like A123's!

One thing that I saw first hand the other day on my Bandito was my rudder slightly binding in the heat at Oakdale. All the flight controls are tightly faired for aerodynamics but I had to use a little 800 grit to clear out the threshold of the rudder surface that was rubbing against the top of the fixed fin. I thought, "wow, that could have taken out the whole jet on a marginal battery or even prehaps a good battery if it were bad enough". It's amazing, structurally, what happens in an airframe when loaded up with G's (based on full scale testing programs and evidence in RC). Hinge lines are no longer straight, controls flex and push against servos causing stall and massive loading - it can be a hostile environment for the RX electrical bus, wires, and the RX battery.

How does this relate to the Spark? Well, it's just another example of a extremely capable modern EDF with a lot of servos. I'll try to stay out of the discussion, as I only admire all your Spark work from the spotter's position and don't have one (yet) of my own
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Old Jul 26, 2009, 06:08 PM
Xtreme Power Systems
Lake Havasu, AZ
Joined Jun 2005
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Eddie, the problem is even more common with those using speed controllers with built-in BECs. People are flying these medium sized 3D planes with 4 servos and can't understand why their plane locked out and crashed right after doing a snap roll. A 3A BEC can't handle that kind of a load, and it is a real dis-service to modelers when manufacturers try to claim that the BEC is good for "4 to 5" servos without stating what size servo. When an HS-55 (the little blue ones) can draw 3/4 of an amp on stall it is easy to see that 4 of them in a snap condition could put a 3A (4 x .75A) load on the power system. Imagine what bigger servos do.

Lucien from Scorpion posted some info their vendor area about BECs used in their speed controllers. This is something that everyone should read, especially since it is coming from a manufacturer.

Hang in their Eddie, I am sure a Spark will be in your hangar before you know it!
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Old Jul 27, 2009, 08:46 PM
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techspy's Avatar
USA, NC, Matthews
Joined Aug 2008
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Ok, so I got the Jet1A mains retracts and struts in today and have them mounted. Couple questions though...

When you have to make new screw holes to mount the retracts but they are too close to an old set of holes, what the best way to fill in the old hole for strength? Epoxy?

I know that it is recommended to have a slight amount of tow-in on the mains, but with the flat spots already on the hardened steel pins, I can't adjust the tow. One main is straight, the other has a bit of tow-out. I imagine that on grass it won't matter too much, but what about on pavement? Will simply correcting with the rudder/nose wheel be enough to control it ok?

Now that I have the final (hopefully) retracts in place, I am going to want to re-glass the area to fill in the openings that were made for the circle spring on the wire retracts. I see that I can order the paint from Comp-Arf, so what material is best to fill in the hole? Just use fiberglass resin and cloth?

Lastly, the Tamjet brakes will work with some modification such as grinding down the attachment points on the back and drilling a pin to keep the whole thing from spinning. Do you think this is worth doing or does anyone know of a thinner "generic" brake hub that will work?

Thanks guys.

Edit:
I guess the disc brakes here will work. Not too bad for $90 a set, but they may be too big.
http://www.altecare.com/wheelbrake.htm
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Old Jul 28, 2009, 07:32 AM
Watt me worry?
Madmax1965's Avatar
Florida
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Techspy I have had good luck with the BVM brakes and wheels.
http://www.bvmjets.com/Pages/wheels.htm#Construction
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Old Jul 28, 2009, 07:39 AM
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techspy's Avatar
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Looks nice. I guess the 2 5/8" mains set would work but $174? Also, how do the connect to the strut to prevent the hub from spinning? Anyone have any experience with these on a Jet1A strut?
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Old Jul 28, 2009, 09:17 AM
Watt me worry?
Madmax1965's Avatar
Florida
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Techspy the brake hub is held in place by a "slot" cut so it snugs against the LG strut.
Here is a shot of how the brake hub is held in place. I like these brakes because they are very smooth in their stopping power. Talk to the peopel at BVM by phone....they are lots of help.(I wish I could afford their planes)
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Old Jul 28, 2009, 12:46 PM
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techspy's Avatar
USA, NC, Matthews
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Thanks for the info. My axles are 4mm however. i guess I could drill the strut out to 5, but I would not want to weaken it.

Wait, maybe it is 5mm, I will check.
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Old Jul 28, 2009, 02:02 PM
EDF Jet Jam May 2014
Robert Belluomini's Avatar
United States, KY, Crestview Hills
Joined Dec 2000
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Tips

Here is what I suggest

Quote:
Originally Posted by techspy
Ok, so I got the Jet1A mains retracts and struts in today and have them mounted. Couple questions though...

When you have to make new screw holes to mount the retracts but they are too close to an old set of holes, what the best way to fill in the old hole for strength? Epoxy?

JB Weld is perfect for filling the hole

I know that it is recommended to have a slight amount of tow-in on the mains, but with the flat spots already on the hardened steel pins, I can't adjust the tow. One main is straight, the other has a bit of tow-out. I imagine that on grass it won't matter too much, but what about on pavement? Will simply correcting with the rudder/nose wheel be enough to control it ok?

You can order 4mm pins from McMaster Carr or PM you address and I will send you a handful

Now that I have the final (hopefully) retracts in place, I am going to want to re-glass the area to fill in the openings that were made for the circle spring on the wire retracts. I see that I can order the paint from Comp-Arf, so what material is best to fill in the hole? Just use fiberglass resin and cloth?

Lastly, the Tamjet brakes will work with some modification such as grinding down the attachment points on the back and drilling a pin to keep the whole thing from spinning. Do you think this is worth doing or does anyone know of a thinner "generic" brake hub that will work?

Thanks guys.

Edit:
I guess the disc brakes here will work. Not too bad for $90 a set, but they may be too big.
http://www.altecare.com/wheelbrake.htm
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Old Jul 28, 2009, 04:57 PM
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monkamarm2000's Avatar
NorCal Silicon Valley
Joined Aug 2002
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just no need to overkill wheels and such on this plane, remember even the heavier electra isn't running big heavy aluminum wheels and big brakes, they just eat up weight and performance in E world


Barry
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Old Jul 28, 2009, 05:09 PM
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Joined Aug 2008
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Thanks Robert! PM Sent.

Yeah I know I don't necessarily need anything big with wheels brakes. I think I will try to modify the Tamjet brakes to fit. I will post any update when done.

Thanks for all the help guys.
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Old Jul 28, 2009, 06:09 PM
Watt me worry?
Madmax1965's Avatar
Florida
Joined Mar 2006
3,862 Posts
Barry:
remember even the heavier electra isn't running big heavy aluminum wheels and big brakes


Barry do you own a set of BVM wheels/tires/brakes? Your statement is sort of general. Most all the planes I have seen in the Electra size (and up)use brakes. If you have a super long landing field you could probably get away without brakes on any plane.....however.....most flyers don't have a field for landing these heavy(I said heavy) planes onto and the Spark is a heavy plane for it's size. You are right about not adding anymore weight but then you take a chance of tearing the LG out of the plane by running off a short runway......so there you go. The BVM brake/tire/wheel is a very lite setup...would I install them on a Spark.....Nope not unless I needed brakes.


I probably would not worry about brakes on the Spark unless I had a very short runway. I have the BVM brakes/wheels/tires on my F-86 and they work very well indeed and I do need the brakes for the Sabre.
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