RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hi Vincent, the wing Brenner has is not the elliptical wing but a modified Spark Dynamic wing, it looks hard to build but with the jigs and interlocking spars/ribs it’s not too difficult to build, if you've built a foam wing you can build this wing. I've never sent a built wing/stab international but if I assume a box 35"x20"x6" FedEx is $344 for 3 days, USPS Global Express (3 days) is $190 and Express Mail® International (3 to 5 days) is $75. With any of these shipping options I am concerned about the wings being damaged and unusable after you receive them that's why I think the kits would be a better option for you, do you know someone that can build for you in France?

If you have any questions about the wings or kits please email me.

Dave Snow

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hey Dave,

In my experience, most of the time damage happens when stuff is shipped in thin cardboard boxes without adequate internal support and packing, but if you use a fabricated plywood box, wouldn't the wings stand a much better chance?

Brenner ...

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

My colleague Steve and I now have our second Contra setup installed and flown, they both use the Neu F3A motor. There seems to be a big difference in the feel of these motors. On one drive when holding the rear prop and turning the front one it rotates in a series of audible and feelable clicks as the motor cogs strongly as it turns. If you let go both props and rotate the front one there is enough cogging stiction to rotate the rear prop through the Contra gearing without the motor turning at all. On the other drive holding the rear prop and turning the front one produces a barely audible and feelable click.

On the 10.15:1 gearset and mixed 22 x 20, 22 x18 props one "cogging" drive draws around 80A static and the non cogging drive draws 83A static. This is with different batteries. Both have similar perfomance in the air (Asyuler airframes).

Anyone else experienced different cogging behaviour with Neu motors?

Malcolm

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hi Malcolm,

Whilst I can't speak for Neu motors and the strength of their magnets or consistency in build, I can say that my AXI out runners have very strong magnets that really give it a notchy feel when turning the prop by hand. On a Plettenberg out runner you can hardly feel the magnets when turning the prop. They obviously both work quite well. From my RC & Slot car days, the stronger the magnets the better. Some were so strong that you could hardly rotate the armature by hand...

Recently in this thread someone was commenting on the Hacker C50 drawing more current because the shaft had rotated in the magnets. Perhaps this has something to do with the current difference? On the other hand, it could just be production tolerance..

Cheers,
Jason.

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hi Malcom, have two new types from autumn last year. They feel the same. Cogging is mild like what is felt with a Plettenberg.

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hey Malcom,

The Neu motors have a lot more "cogging torque" than the Hacker C50 motors, so that's normal. As for the differences from one setup to the next, the gearset in the Contra Drive will free up over the first few few flights for four possible reasons:

1/.. The grease is channeling out of the way of the gearset, which will reduce friction after the first few flights.
2/.. The gearset is designed to "self-align" as it runs, so if a unit is assembled with the gearset slightly misaligned, it will self align during the first few flights.
3/.. The rear bearing in the rear hub is designed to "float", which is what allows for self-alignment. However, if you dig a prop into the grass when you taxi back to the pits, or something similar, this can knock the rear of the driveshaft off-center, which you will be able to feel when you turn the unit by hand, but this will correct itself when you power up for your next flight.
4/.. There is also a tolerance on the fit of the planet gears to the ring gear, and the pinion gear to the planet gears. This means that some gearsets will be free from the start, but others might be snug. Either condition is fine, but if you are comparing one unit to another side by by side, you might be able to feel the difference.

As far as current draw is concerned, I wouldn't worry too much until you get the chance to compare both units with the same pack in the same state of charge. Batteries can make a huge difference in current draw. I usually pick up at least 10 amps when I use 30C, or 65C packs.

Brenner ...

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hi Brenner,

I'm not worried about the cogging and I'm pretty sure there isn't an alignment problem in the drive as it takes virtually no torque to rotate the front prop and turn the rear prop with the planet gears "walking" round the stationary sun gear on the motor, rotating the ring gear and the gear case. There are no tight spots or noises when rotating through several turns so I'm sure the gears are well aligned.

This is a motor issue. Two motors, both marked the same and from the same supplier but one cogs more than the other. I have run Hacker C50s, Pletty Extras and Advances so know that some motors cog more than others. I'm just a bit concerned that two of the same design seem to act differently.

Malcolm

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

If you want to measure RPM I suppose the easiest way is to use an eagletree logger with dual rpm sensors. Log the motor rpm using the brushless motor rpm sensor and then the rear prop rpm using the magnetic or optic sensor. Then use the gear ratio to calculate the front prop rpm.

It makes me wonder about how the gear ratio is defined for this unit. Is for instance 10.33:1 the ratio from motor to prop if each prop is spinning at the same rpm? Or is it the gear ratio given as if the outer ring is locked in the same way as a normal planetary gearbox?

It would be quite interesting to log the rpm, and especially on the popular mixed prop setup. Existing theory on contra props actually suggests that the rear prop should have a lower geometric pitch than the front prop (for equal power and rpm). This is because the rear prop operates in the swirl of the front prop and thus sees a higher angle of attack even if the geometric pitch of the two props is the same. The velocity increase at the rear prop should be marginal and not enough to motivate a higher pitch. Theory and practice however do not always agree. It would be interesting to know more why a higher pitch rear prop is experienced as a better setup (if I have interpreted the impressions in this thread right). Anyone tried with the higher pitched on the front??

/David

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hey Reko,

I have tried a higher pitch prop on the front, and the system seems to behave the same as when the higher pitch prop is on the rear. My theory is that the planetary gearset automatically adjusts the rpm of each prop to compensate regardless, so the net effect is like changing the equivalent pitch of the system. For instance, a mixed set of 22x22, and 22x20 props is like an equivalent system that has a 21" pitch, although the equivalent diameter is considerably larger than 22".

The gear ratio is calculate with the assumption that the props rotate at the same rpm. Obviously this is not exactly true, because the relative rpm of the front and rear props changes throughout the flight as flight conditions change, which the net effect being that the actual gear ratio for each prop also dynamically changes throughout the flight as flight conditions change.

Brenner ...

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Are you using the same ESC's between these two motors?

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Tony,

A very good point!

They are both Jeti controllers, mine on the cogging motor is a Spin99 the other is the slightly earlier version supplied by Hacker with the first C50 Comp motors so no not exactly the same. What I can tell you is that my cogging motor felt the same before and after it was connected to the ESC. I can't speak for the other one I've only felt it connected to the ESC.

Malcolm

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

I finally got around to blending in the flair to match the rudder on my Nuance. I used what I had available but I am happy enough.

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hi Malcolm,
Besides the gear fit/alignment already mentioned re how the cogging feels through the drive I think there is another factor.
Peak motor temps may have a role here.
I think that one hot run or many hot'ish runs de=mag the magnets slightly.
So far I have run 3 motors - 2 still perfect - one with a front bearing gone noisy (old type Neu).
The cogging was/is the same with all of them - very evident , almost disturbing.
I pay close attention to cooling so none of my motors ever got above 45 to 50C.
Angus's ,with 'some' hard flying, had the cogging fade away all-together !!!
BUT ; His mAh draw increased substantially as the season got towards the end ,while his flights remained the same - you know how consistant he is.
A lot of the cogging in his reduced rapidly in the early flights.
He is pulling the motor to send it for a service/upgrade.
I believe it is substantially de-mag'd.

Brian

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hi Brenner,

Good to hear that you and Bryan Hebert are teaming up to produce a contra drive specific airframe. The Allure...

Cheers,
Jason.

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hey Jason,

Yes, I'm very excited to have someone with as much knowledge and experience as Bryan try his hand at developing a Contra specific airframe. I'm really looking forward to seeing how Bryan can leverage the benefits that come with a Contra Rotating System through careful, thoughtful airframe design.

It's happening it just the right time too, because over the past year a lot of very talented and experienced pilots have had the chance to try Contra powered planes, and consequently, as a community I think we've learned an awful lot about how Contra systems work, and what they can do, and now Bryan will be able to integrate all of these new learnings with his own considerable knowledge.

Brenner ...

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

I heard he'll be hooking it up to a YS175 CDI.:D

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

I have taken delivery of my Contra Drive and I must say the quality of workmanship and attention to detail is outstanding. Well done Brenner and team for making this product available to the comsumer market.

I have a question in relation to the Hyde mount and Neu F3A motor setup when using the Contra Drive.</p>

The following photos show the complete assembly with the drive, motor and mount. I assume that the Hyde mount is installed as shown however the mount covers the cooling fan section of the motor. I cant rotate the mount 180 degrees because the hub of the contra drive is too wide for the mount.</p>

1. Am I using the correct Hyde mount?
2. If I am have I assembledall the components correctly?
3. If all the above are correctwill cooling be and issue in this configuration or do I have to modify the mount?

<br type="_moz" />Thx

Peter

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hey Peter,

One thing to watch for when you use a Hyde mount is that the M4 button head cap screws that we supply with the adapter manifold should probably be a little longer to compensate for the thicker front plate on the Hyde mount. Here in the USA we get these screws from www.mcmaster.com, but I'm sure there are alternate vendors in Australia.

Brenner ...

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Peter
Cooling not an issue. I have used this setup on three different aitcraft.
Dick

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

We've been experimenting with different props with an eye towards cutting a new set of molds for a "short pair" similar to Chip's APC props.

What we've done is take a 22x20 front prop and cut it down to 20.5" diameter, and a 22x22 rear prop and cut it down to 20" diameter. We also rounded the tips as well. The resulting props are shown in the attached picture.

It turns out that these "cut and hack props" seem to work quite well. The speed range is huge. They pull my Integral through the air faster than any 2m plane I've seen. (including Andrew's Spark..) I've flown them back to back with Chip's APC props, and they seem faster, but they draw an extra 200 mah out of my packs, which I'm assuming is because these props have wider blades than the APCs so they load the motor more.

The noise is similar, and our working theory here is that this is in part due to the difference in diameter from front to rear. The thinking here is that different diameter props run at different rpms, which eliminates any syncopation sound, and having the diameter of the rear prop smaller than the front keeps the tips of the rear prop out of any vortex turbulence that might be coming off the tips of the front prop. (for the aerodynamicists out there, I welcome your rebuttal and contrary theories ..)

I'm running these props with a tired set of Thunderpower 25C G6 packs from last year, my 13XL motor, and a 10.33:1 gearset, and I'm drawing 3400 to 3800 mah from my packs, (AMA Masters Pattern ..) which I'm very happy with, but I know that I can draw more with the higher gearsets, and I also know that there are pilots who would like to draw less so that they can fly 4400 mah packs.

So based on this, I'm inclined to go with similar pitch and diameter, but narrower blades. This should give people the option to either dial the mah draw from the packs back so they can use 4400 mah packs, or dial the performance up so they can go pylon racing...

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hey Brenner
Looks good. I am currently running the 9.89 gear set with the 22x20 rear and the 22x18 front and only use 2900 to 3000 mah on my TP G6 4400's flying the F13 sequence. I think the Neu motor is more efficient than the Hacker 13 wind. I do not believe I would have any issue running the cut down props as far as staying in the 80% rule with the 9.89 gearset! I will let you know as I am cutting down a set as we speak.
Dick

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hi Brenner,

How was the downline braking with the modified propeller and gearset combination.

Regards,

Peter

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hey Peter,

I used about 30% ESC braking, and it was excellent. My downlines were slower than my uplines.

Brenner ...

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

I would have to ask why you want to narrow the blade profile Brenner?

You have another step of gear ratio available to anyone who wants to lower their amp draw as it is. We have always found that wide blades pull better and are easier to dial in the throttle curve than narrower ones.

Malcolm

RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes
 

Hey Malcolm,

This is what we are debating right now. Dick Mundee is going to try these modifications with his setup, and if he can successfully fly F13 with his 4400 mah packs using the wide props, then it will make a strong case for leaving the blades wide.

The other side of the coin is that not a lot of people have purchased our 10.56:1 gearset, and I think these people would prefer a set of props that gives them maximum flexibility with the gearsets that they do have. We're not in the business of selling more gearsets, we want to develop the ultimate power system for f3a pattern, and the ability to swap props without changing gearsets has value I think.

I envision a system where you have one set of props for days without wind, and then a second set of props for days with a lot of wind, and the gearsets are used to match the Drive to different motors, and different airframes.

Brenner ...