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Sep 02, 2004, 06:10 PM
Thread OP
Question

OV-10 Bronco power system


I have decided to build a speed 400 OV-10 Bronco from a set of free plans. Has anyone built one? If so, what did you power it with? I am looking at two brushless motors, either AXI outrunners or Ultrafly direct drive set ups. Could anyone recommend a motor size for me please. Wingspan is 1m, but I have no idea of AUW as there is no info besdies the plan.

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Sep 02, 2004, 10:24 PM
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davidleitch's Avatar
I've seen a video of a bigger Bronco flying on two Hacker B50s and it was awesome. Fast passes 1 metre or less off the ground.

Two motors obviously will take a fair size battery to handle the current draw. You will likely be around 40 amps (20 per motor) at least.

1 metre is not much info. However if we work off an all up weight as a first pass of say 1.3 -1.5kg (and that might be right off) = 3lb say then 10 cells at 40 amps gets you in the ball park at around 400 watts.

So that's two Mega 16/15 xx geared or direct drive or axi equivalent. How scale are you trying to be and how much ground clearance will you have for the props?

Just trying to think out loud here.

sounds like an interesting project
dave
Sep 03, 2004, 04:08 AM
Registered User
Tim Trick's Avatar
1 meter wing span is not a lot and you would be best advised to try and keep the weight below 1000 g if possible. I am not totally sure what the chord is for your scale, but I am guessing some where in the region of 18 cm. this would give you approx 18 dm2 (1.93 squ. ft) of wing area.

The wing loading would then be approx 55 g/dm2 or 18 oz/squ.ft -it should fly at that.

I have success at 15 watts per 100 gram input for ROG (hard surface), so you would need at least 150 watts. Divide that per motor and you thus need 75 watts input each side. Using an 8 cell 1950 FAUP pack at 325 g would give you under load 8 volts, thus a current draw at WOT of around 9.5 amps (per motor).

You need to keep the weight down as much as possible, so I would look at the smaller AXi outrunners, say AXI 2212/26. This can spin a 9x6 APC E prop at around 6000-6300 rpm, pulling in the region of 9-10 amps:

http://www.flyingmodels.org/motortest/Link_e.htm

This would give you a theoretical pitch speed of approx 57 kmh at WOT - should be easily enough to ROG and fly level. With two Jeti 18-3p controlers, Two AXI 2212/26 motors, 8 cell 1950 FAUP pack - your power train will weigh in the region of 495 grams. That leaves you approx 500 grams for the rest of the radio gear and the airframe - should be possible .

Cheers

Tim
Last edited by Tim Trick; Sep 03, 2004 at 04:27 AM.
Sep 03, 2004, 05:56 AM
hul
hul
Registered User
hul's Avatar
I use 2 speed 400 6V, geared 1.85:1, APC 6x4E, one PQ 2200mAh 3s1p pack (rated 10C) for both motors to power my 1.1m Mosquito. Weight is about 900 grams, pulls 8 amps per motor. It flies really nice on that setup.

Hans
Sep 03, 2004, 07:46 AM
Thread OP
Here is a link to the plans.
Recommended Power System:
- 2x Graupner Speed 400
- Olympus 2.33:1 gear drive (or similar)
- 6 cells, 2000 mAh
- 9 x 8 propellers
Sep 03, 2004, 12:52 PM
Registered User
Dr Kiwi's Avatar
The owner of my Local Hobby Store, Bob Hargas, has built and flown a huge AV-10 with twin 4-strokes in it, but also a much smaller kit version, perhaps 40" span, with twin MP Jet 25/35-20's running on 3s2p TP 2100's. He would be a good person to ask:

http://www.justrchobbies.com/justrcp...trchobbies.htm

Cheers, Phil
Sep 03, 2004, 04:11 PM
Thread OP
Quote:
Originally Posted by Tim Trick
You need to keep the weight down as much as possible, so I would look at the smaller AXi outrunners, say AXI 2212/26. This can spin a 9x6 APC E prop at around 6000-6300 rpm, pulling in the region of 9-10 amps:
<snip>
This would give you a theoretical pitch speed of approx 57 kmh at WOT - should be easily enough to ROG and fly level. With two Jeti 18-3p controlers, Two AXI 2212/26 motors, 8 cell 1950 FAUP pack - your power train will weigh in the region of 495 grams. That leaves you approx 500 grams for the rest of the radio gear and the airframe - should be possible .
Tim
Do you think 22's will be big enough? I was thinking 2808 size. How do you run two speed controllers? I was thinking of 1 !HM-40 and split the wires.
Sep 03, 2004, 06:20 PM
Registered User
Dr Kiwi's Avatar
2808's weigh 80g each! That's 160g without the mounts, ESC's, adapters, props and batteries and the complete airframe. If this OV-10 is only 40" span I reckon the whole thing needs to weigh no more than 750g! Lipo's will be a lot lighter than an 8-cell 1950.
Sep 04, 2004, 04:37 AM
Registered User
Tim Trick's Avatar
I would aggree with Phil and keep the weight down as much as possible. If you have experience in Lipo's, they would definitely be the way to go - although there is obviously a cost issue involved.

I only mentioned the FAUP's as I do not have any Lipo experience and these NIMH cells are good for high current with low weight and good volt delivery characteristics at such amp draw.

For this size model the 22 series motors will do the job - the main intention is to be able to swing a big enough prop at useful rpm - two 9x6 APC props turning at 6000 rpm + should give you enough static thrust for a good ROG as well as giving a good dynamic thrust in flight. With a 3s lipo pack, the volts would also be higher than an 8 cell pack and the rpm accordingly will be better.

As for the ESC's, it is possible to run two brushless motors on one ESC, but this is not reliable as there may well be start issues. It would be better to use two ESC's and plug the signal leads via a ' Y' conector into your receiver.

Cheers

Tim
Sep 04, 2004, 06:10 AM
Thread OP
So do you think 2212/34 would be the best choice? 4-8A, 6-10cells or 2-3 LiPo's. Prices of ESC's should be good as I only need 10A controllers. I'm trying to do this on a budget, so I am not sure about LiPo's.
Sep 04, 2004, 08:31 AM
Registered User
Dr Kiwi's Avatar
Here's what 2212/34's can do. With 9x5HD on 3s you'll get 14oz thrust at only 4.8A out of each of them. On 8-cells, the 9x5HD will give you a little less, but if you go to 9x6 APC SF you can probably get the same thrust or more at ~5A each.

Bob Hargas couldn't find counter rotating props, but you might get lucky.

Cheers, Phil
Sep 04, 2004, 09:48 AM
Registered User
Tim Trick's Avatar
To follow on,

If you're planning to go to the higher volts (3S lipo's or 9-10 cells NIMH's)then the 2212/34 would be best. If you're planning to stay with Nimhs, at lower cell counts to keep the weight down (i.e. 7-8 cells), then the 2212/26 will be better. The intention is to keep the rpm's up, otherwise your flying speed will be too close to your stalling speed.

As far as the slowfly props go (from both APC and GWS) - once you start hitting 7000 + rpm on 9 inch blades, you are getting very close to the rated max rpm - so high cell count on the 2212/26 with these props is maybe to be avoided.

Cheers

Tim
Sep 04, 2004, 10:53 AM
RC Player
Hi MACR,

I would agree with Tim! You should limit the AUW for a 1m model or it will need speed to support its weight.
If you have 2 exact same KV ultrafly A/30 series motor, you can use Pheonix ESC from Castle Creation to Sync the 2 motors. It will deliver the same RPM on both side. Of course, you also have to use the same size & brand prop. We try this on direct drive and fly it on a Wing. We have not try it with Gearbox yet. This is for your reference. Another motor that has this capability is Kontronic with their smile ESC.

Charlie
Sep 04, 2004, 04:33 PM
Thread OP
Thanks Charlie. I like my ultrafly A/30 on my tiny, but doing a bit of thinking and mesurements, I have decided the AXI would be a better choice on this occasion.
Tim
Quote:
As far as the slowfly props go (from both APC and GWS) - once you start hitting 7000 + rpm on 9 inch blades, you are getting very close to the rated max rpm - so high cell count on the 2212/26 with these props is maybe to be avoided.
Could I use sport bades as an alternative, or would I not have enough thrust? Reading what you say about cells, it appears that LiPo's will be the only way to go. If that is the case, I will have to get over my concerns with them puffing and bursting.
Sep 05, 2004, 06:33 AM
Registered User
Tim Trick's Avatar
Macr,

From my experience, the slow fly props from APC pull more current from the motor compared to the equivalent size ' E' props at the same rpm. looking at the profile of the SF props, they appear to have a greater camber as well as their larger area. This would hold true as they are designed for higher efficiency at lower rpm than the ' E' props.

APC recommend 65,000 divided by the prop diameter as the max rpm for the SF props and 190,000 divided by the prop diameter for the 'E' props.

On my Estar Porter (752 grams, 120 cm wingspan), I had originally fitted an APCE 8x6 to the Axi 2212/20. This turned at 8000 rpm on a fully charged 7 cell KAN 1050 pack, pulling 10.2 amps and giving a theoretical pitch speed of 70 kmh.

This had enough power to ROG and fly at this weight (incorrectly balanced and flying in the wrong conditions caused it to crash on its maiden!).

I have ordered some APC 9x6 SF props, which I will use for this plane. I expect something in the region of 13 amps draw with this prop at approx 6500 rpm. This will give me a slightly lower max speed, but more static thrust for better takeoff authority or acceleration on touch and goes, etc. I have tested a 9x4.5 APCE prop on this motor and pack and saw 6750 rpm at 12.1 amps. providing good static thrust, but the calculated max flying speed was too low for my liking.

I think you will be okay with the APC SF 9 inch props upto 7500 rpm, but would not recommend taking it any higher. The APCE props will definitely handle the rpms, but will not be as efficient at lower prop speeds when flying at reduced throttle, thus you would need a higher throttle setting at this speed than if using an SF prop.

With two Axi motors with 9x6 SF props, your plane will definitely fly (as long as you keep the weight down as low as possible-no UC, just hand launch and land on grass).

I can't comment on the use of Lipo's as I am not using them (too expensive, questionable life of battery and don't fancy the irritation of the required extra considerations for charging and discharging, etc-but that is another issue).

You do not need to use 1950 FAUP's if you want to stay with NIMH's-there are a lot of other NIMH's available that can deliver the amps required and weigh less - but then you will have to accept a shorter flight time. The newer GP1100's look good-I have just ordered a 7 cell pack to try out.

The 2212/26 is good option between the higher Kv /20 (pulls more amps) and the lower Kv/34, (pulls less amps) if you want to just stay with NIMH's. But if you want to try both Cell types, (i.e begin with NIMH's and then swap over to Lipo's), then I think the 2212/34 will be the best choice.

Just make sure you get an ESC(s) that can hadle a few more amps above the max rating of the motor - its just too easy to toast an ESC that is rated close to the amps being pulled by the motor (also the bigger the ESC, the more amps and thus servos, the BEC can support without also being fried).

I hope this helps,

Cheers

Tim
Last edited by Tim Trick; Sep 05, 2004 at 06:38 AM.


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