Discussion in 'General Plane Discussion' started by TManiaci, Sep 9, 2008.
Good point Bryan!
Hey Sandman, where is the chit about flight data recording? Bring it bud!
Wo makes like a "Pin Board" that has a bunch of the Dean ultra plugs on it so you can
stack together a bunch of smaller packs?
They make Parallel boards, sold HERE at Tower Hobbies.
I don't think you'll find Series boards, since all you need to do is plug one battery into the next male-female in a string for as many batteries as you need to gang.
I thought it might be interesting to take my favorite motor line and build a table that shows all the models, the specs, and the Wattage and RPMs to make motor selection easy.
As we were discussing, you can see that the kV factors get small as motors get big, and the cell counts go up accordingly. Also note that I only gave ratings for the battery counts that Model Motors recommended in thier ratings. Some of it doesn't make sense where it appears there should be ratings.
BEWARE, my calculations in this spreadsheet are based on 150% of rated Amperage. That means these are BURST Wattage numbers, not continuous.
To use this table, simply find your desired Wattage matches, then narrow your selection by:
a. The RPM range (below 9,000 for SF props, 9,000-12,000 for E-Series Props).
b. Amperage of your system components. (1.50 x the Current Capacity)
c. Battery's available, or planned.
d. Weight of the Motor.
Ill have to post a chart that shows all the different brands and their comparative motors from other manufacturers. If you have a motor, and want to know which motor from another manufacture matches it or exceeds it, let me know.
Just bought a 58 inch Extreme flight 330 with a A40-14s, speed cont, and 15*8 zoar eprop, and 4250 mhr 4 cell. I bought this as a complete kit from Chief (I had a credit) I'm a little leary about the performance of this setup. Wondering if the t-man or bd had any experience with this motor?
Battery, assuming it's the FlightPower EvoLite 17C 4250 mAH, 72.25A, 1056 Watts capacity.
Hacker A40-14S, 530kV, 40A/70A, 1036 Watts on 4S1P (NICE)
With the heavier 4250mAH, you'll be all of 5lbs (80 ozs)
Power to weight ~ 13 W/oz.... SWEET!
You will love this rig. That is pretty strong, and the Hacker quality is top notch. Smooth and quiet, you are set dude!
What speed controller is it equipped with (say it's the Airboss 80 please!) You don't want to be strapped to 60 amps, you need to pump that baby at 70 amps WOT.
It comes with a wimpy phoenix 60 I have a 90amp scorpion pro with a seperate castle bec,battery is 20c constant 40c bursts 14.0z pack by Steve Neu. I'm going to leave out the pilot and go light as possible. This plane should ROCK!
Sounds like a hot setup Joe... can't wait to hear about the first flights.
Hey Sandman... You gonna spill the goods on the Flight Data Recording stuff?
Guess Sandman is too busy to post about in-flight data collection...
So, one point that was not addressed, thought I would hit that.
Wiring gang batteries, ALWAYS use identical batteries:
With Series packs, if you connect packs of different capacities, the smallest pack will be discharged without good voltage feedback to the ESC. This will likely ruin the smaller pack, possibly overheat and swell, and in worst case conditions, make your airplane a flying flare.
This is important with Parallel sets of packs too. It is vital that when hooking up parallel pack sets that all the packs are the same mAH capacity. They also must be charged to the same voltages. If you connect two cells, one charged and the other not charged, look out! The charged pack will try to discharge into the dead pack, but without any current limiting safety. Current will go nuclear, and a meltdown is inevitable. This is not hard to do if you don't manange your aresenal of packs and know exactly what state every pack is in at any given time.
For those that want to understand electrical theory a bit better, we make an anology to fluid systems.
Think of Voltage as pressure, and Current as flow in a fluid system. Fluids (Current) will always flow toward low-pressure (Voltage). If you want to force flow (to perform Work), you create a pressure differential.
Same in electrical systems... Create a Voltage differential to make current flow. Current flow does Work, by generating magnetic fields and/or heat.
A Diode? That's a one-way valve.
A Resistor? That's a flow restriction to regulate flow rate.
A FET or MOSFET? Thats a controlled switching valve.
A Capacitor? Like an accumulator with an Air Cushion inside to damp pulsation and store pressure.
A Battery? Same as a Capacitor, but with much more pressure storage potential.
Hey Snap... ever get this thing in the air? How did it perform?
Thought I would offer another installment in the E-Power 201 series here.
Installing a UBEC...
So, my DW Foamies 48" Juka has HS-65 servos, and I was getting serious "blow-back" on the control surfaces, most notably on the ailerons at higher speeds. Blow-back is generally the term used to describe when the servos(s) are maxing out the torque and the surface either won't go to the endpoint, or it pushes and then fades back from the max throw. The HS-65 is the recommended servo for this airframe, but I find it too weak for my taste. Snaps at speed were lazy and slow, rolls were not brisk and unless you were flying at stall speeds, everything seems washed out and weak.
One solution was to put in bigger servos... expensive, messy on a foamy to replace with new mounts, etc. The other potential solution was to get more out of the HS-65's by bumping up the voltage (power). A standard BEC built into most ESC's are limitied to 3 servos and less than 3 amps at 4.8 volts. Running 4 servos on big surfaces canpotentially push current demands over the edge, and you risk losing the plane to a BEC shutdown by overload.
A UBEC is a separate power source, which provides much higher current capacity and also the opportunity to run controls at 6 volts. Boosting servo power from 4.8V to 6.0V drastically improves servo performance. In large scale electrics, it is common to use a UBEC, and generally provide a separate battery pack for that purpose for added safety, isolating control power from motor power so when motor power is drained, you don't worry about control loss. The risk of large scale e-power aircraft suffering catastrofic power loss seems to be considerably higher than on smaller aircraft. It appears most common to include a UBEC on systems exceeding around 600 watts. Most of the big high-voltage and high-current ESC's don't even have a BEC built in.
In the case of smaller electrics, it's okay to grab the power from the flight power pack without much risk of power failure. On a 3S pack, your LVC is prolly around 9V, so you are safely above the 6V level. Power system reliability is really sound on these sub-600 watt systems running 3S or 4S power.
The UBEC is a surprisingly small device. In this case, I used a $7 UBEC from Hobby City, rated at 3 amps continuous and 5 amps burst with swithing regulation (better).
I simply stripped a short bit of wire on the battery leads from the ESC and soldered in the UBEC power leads. They are separated well, so I didn't even take the time to insulate them.
Now that there is a new power source in the system, you must disconnect the BEC power lead (RED) from the ESC. Just lightly depress the little exposed tab in the connector and the brass plug will release as you pull. Pulling it out of the connector and folding it back will leave you the opportunity to replace it later if you want.
A little electrical tape will insulate it...
Mount up the UBEC on some Velcro. Now you simply plug the UBEC into a spare channel or a splitter on your Rx. Replace the BEC line from the ESC so you still have Throttle control signals to the ESC, and you're golden.
In my case, the change was dramatic. The extra 25% torque and speed changed the airplanes performance in a huge way. Now, speed or not, the control authority is far better. I'm very pleased with this $7 inventment. I see no blowback now, and the big BAF really reacts briskly to your control inputs.
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