Hi Guys,

I am new to the sport, thus the beginner post...

I started on a 4 CH motorized glider (400 brushed) last year. I think I have the hang of it and really enjoy it.
Last month I bought the VMAR Bird Dog ARF and i need some help setting it up.

It is 43 inches span, 29OZ. The recc motor is a 100-180 Watt Outrunner. I picked up a 178 Watt / 3800 RPM motor.

questions:

1. Only some engines that are forsale provide power in watts. How do I find a similar power engine with different ratings? Should I get less RPMs for this plane?

2. How do I select a good prop for this bird? I am thinking more power and time aloft than speed.

3. Radio question: when buying a radio does the receiver and TX have to be the same MHZ, then jsut swap crystals to change freq?

There is an electric motors forum where you would probably get better responses....

Welcome to electric stuff, where motor selection is an in-exact science at best. Companies don't really have a standard unit of measuring electric motors unfortunately. With a little experience you can find a good match though. I'll do my best:

I'd recommend about a 950kV outrunner. That should be rated at 16-18A. For a speed control, you can't go wrong oversizing the ESC. I'd go 25A. It'll handle the heat/current draw better and give you a little more buffer if you run the plane hard. Cost difference is minimal.

For prop selection, that'll be listed on the specs of the motor. You'll want a larger diameter, low pitch prop to fly slow with lots of torque. The larger diameter moves more air over the wings at a slower speed...... You're creating your own lift. With that 950kV motor, expect a 12x4 prop maybe? I think GWS makes a 12x3.75 or a 12x4.7

A 1200-1600mA 3-cell LiPo should give you 10-15min flight depending.... It's best to get a battery with a balance plug on it.... I'd also highly recommend getting an ESC with a balance port on it. That way the ESC knows what the individual cell voltages are instead of the average V of the whole pack and risk bringing one cell too low and damaging the pack like I did yesterday....

The transmitter and receiver should be 72Mhz for aircraft use. The "channel" is actually a deviation from 72Mhz...... 72Mhz is the base frequency, the channel is 72.xxxxMhz. You have about 50 channels. You buy a rx crystal to match whatever channel the transmitter is, never the other way around. Lastly, there are several different types of crystals, so a channel 45 crystal that works in a HiTec may not work in a Futaba....etc. Buy the channel crystal for the brand rx you pick.

You can only change the crystal (legally) in the receiver, unless your transmitter has a module.

When you swap crystals you have to make sure the shift is the same, whether it's dual conversion, and if you have a Futaba radio, make sure the receiver is tuned for the frequency you want to change to. Either high band or low band.

This is all explained in more detail [link=http://www.hooked-on-rc-airplanes.com/rc-frequencies.html#3]here[/link].


ps.

Hey Spiral, that's the coolest Avatar I've ever seen!

Thanks so much. So the motor I have at 3200RPM is too much? Everything else sounds super.

I understand the channel changing response as well. I think I mis-spoke.

HA! thanks! Unfortunately, the avatar was based on actual events. [] NOOOOOoooooooooooo!

I don't think you mean 3200rpm.... I might be wrong, but check it. I think you mean 3200kV! Which would be used on a 150mph delta wing or something. That's high power, really stinking fast.

Right Spiral.

Here are the specs:

3200rpm/v 178W D2830 RC Brushless Motor Details

Specification:
Model : D2830-3200
KV (rpm/v) : 3200
Voltage (v) : 11.1
No Load Current (A): 2.2
No Load Speed (rpm) : 36000
Load Current (A) : 16.0
Load Speed (rpm) : 4300
Recommended ESC : Turborix Advance 30A ESC
Propeller : 1047
Pull (g) : 410
G/A : 25
Weight : 50g (±5g)
Packaging Weight : ~110g

it was 3200 per volt of course.
Too much for this acft?

As spiral says, that motor produces a lot of RPM's but much lower torque than say a 950kv motor.

That motor could be used on that plane, with a reduction gear drive, but I do not know if you have the room to put all of this in the cowl.

A 3-1 reduction gear drive system would put you where you want to be with that plane. You could also increase the prop diameter for more thrust too.

Thanks. So a 950 would be a better fit? I'll save the 3200 for a higher performance model as i progress. Right?

With the recommended 11.1v lipo that would be in excess of 33,000 rpms. you want somewhere near the 10,000 or so rpm range with an airplane.
Edit: The specs for that engine are confusing, it recommends a prop and battery, gives a no load rpm of 36,000 rpm which is just about right then give a load rpm of 4,300. If that is true this is a very weak motor to drop that many rpms under load and 4,300 rpms is too low for most airplanes. Very confusing.

Yea, I'm afraid so. I just don't think you will ever be able to use that motor on that plane unless you run a gear reduction (as suggested by someone). Save the screamer for a delta wing or something.

These brushless systems are pretty expensive... I bought a Turnigy 950kV motor from Hobbycity.com or hobbypeople.com don't remember which, but it was $18. Believe it or not, it's turned out to be an absolute fantastic motor. I can't believe it was that cheap. I think the motor you will require is also known as a "400 size".

Seriously consider the balance leads on the battery and ESC though. I'm not sure what the cost difference will be.

As Missleman pointed out there is a serious RPM drop with the recommended prop. I wonder if the motor provides sufficient torque for any direct drive, short of a DF setup?


Yup, most the "brand name" motors are made in Asia anyway.

These no-namers may have slightly lower efficiencies, but for the price they have been fantastic for me.

You guys have been very helpful. This sort of forum is exactly what a newbie like me needs to get started correctly.

Here is a motor I am looking at for this 29OZ VMAR Bird Dog with the stats. Does this seem to be a good fit?

TR 28-30B 14A 1050Kv Brushless Outrunner

Model: TR2830-1050
Max Eff: 12A
Max Load: 14A
Kv: 1050
Weight: 57.9gr
Pull: 400~900gr
Prop: 10x5 or 10x6
Voltage: 6~10v
No Load Curr: .9A
Size : 30mm

Thanks again

Plenty of power, right speed, add a 25amp ESC, a 3s lipo and a 9X6 or 10X5 or so electric prop and you should be set.
(I know the max load is 14amps, I suggested a 25amp ESC so it will stay cooler, a smaller ESC will run hotter)

Perfect. I'll go for that.