Brenner

Hey Paul,

Yes, that's the plan. It will actually be possible to adjust the gap between the spinner backplate and the nose of the plane using spacers.

It will also be possible to use a smaller motor plate and fit the Drive into smaller spaces than the V3.

Brenner ...

pippy

Good plan Brenner. Would love to see a breakdown of the workings?

Brenner

Hey Paul,

Here's a cross section.

Brenner ...

.

pippy

Does it have the same clutch arrangement as the V3?

Brenner

Hey Paul,

No, this time we are keying the ring gear to the gearcase to prevent rotation. Also, the ring gear will be held in place with a compressed o-ring, so that it stays with the gearcase when the Drive is disassembled.

However, there is still a spring in the system that preloads all of the components. This spring will hold everything together during operation, but when the rear hub is removed, this spring will release all of the components, and then everything should come apart easily for servicing and replacing parts.

We are also going to use roller bearings for the planet gears instead of ball bearings, and these roller bearings are oversize, so they should last the life of the Drive and never need replacing. Same for the bearings.

Brenner ...

serious power

Hi Brenner,
Great weight - put that with your proven ,very well proven, track record and you have a winner.
Good timing too
You have the F3A world ,if not already using a contra, talking about using one. This will add more momentum to the move.

What parts, if any, are in common with previous versions ??

Best of luck with the testing - if you need a guinea pig !!

Brian

pippy

That sounds like great developments. Thanks for the info.

Brenner

The only parts that are common with the V3 Drive are the rear spinner, the front hub, the front spinner and the props.

Everything else is different, including the motor.

One other feature that we are trying to include with this Drive is the ability to considerably extend the greasing interval. We have an internal grease reservoir, and a grease recirculating system that we hope will extend the greasing interval to beyond 200 flights.

We'd like to get to the point where the Drive only needs greasing once a year, but that's going to require testing to prove.

Brenner ...

serious power

Hi Brenner,
What will the story be re the motor - will it be a special for this ?
Will there be the same options re gearing ratios/gearsets.

Brian

Brenner

Hey Brian,

We plan on using an off the shelf motor, and then adding a second front bearing to it to make it robust to axial loads. It should be possible to use a wide variety of motors without having to have an adapter for each one.

Right now we are focusing one specific gearset. We can make others if the need arises, but we'd prefer to have things working with a single gearset, and then change the motor kv if the power output needs to be adjusted.

Brenner ...

serious power

Hi Brenner,
That's certainly a different approach.
Not that that is a bad thing - they say that 'there are many ways to skin a cat'.
One or two additional props in the range may be worth considering to restore some user options - say a 21" pitch rear and 19" front.
Of course I'm saying this while not knowing what motor options are going to suit this. All very interesting.

Besides bearing life/service intervals the main thing I see in this is the weight.
The saving will allow a lot of current, large, models carry 5000mAh or more battery capacity instead of being stuck with 4400's so as to make weight.
It also looks like you could do a much smaller set of spinners, diameter wise, as an option.

Brian

Brenner

Hey Brian,

All options are open at this point. We can certainly consider special gear ratios to match up with specific motors.

Brenner ...

serious power

Brenner,
That's really great to hear.
Is the V4 mounting directly to the motor shaft via a taper lock or something ?

Brian

Brenner

Hey Brian,

Yes, the Drive will clamp onto the motor driveshaft using a tapered collet with a taper lock.

Brenner ..

villalbi2003

Hy brenner
very good solution for bearing and for weigh reduction,
i worry about the the link system to motor, with this new system you have all gearbox propeller and spinner without any
support, so what can do is to broken the motor shaft closer to conical clamp,specially if you have a little unbalance into
propeller /gearbox parts, Do not think is possible?
In any case very good solution for all new solution
Alberto

Brenner

Hey Alberto,

Actually the design intent here is to take advantage of two specific features of Contra Drives.

1/.. The lack of shaft bending moments due to the contra rotating propellers.
2/.. The need for rubber mounts due to the blade passing frequency of the spinning props.

The lack of bending moments means that, for the most part, the only forces on the system are substantially axial, and a large diameter motor rotor shaft isn't needed to resist bending moments.

Also, using rubber mounts in the system lowers the first resonant natural frequency of the mounting system to an rpm that is about 60% or so below the max rpm of the props so that the Drive passes through it as the throttle is advanced. This has the effect of practically eliminating the stiffness of the mounting system and isolating the airframe from the effects of unbalance when the Drive is spinning at max speed.

What this means is that any unbalances in the system will just cause the Drive itself to shake and any vibration forces that result will be isolated from the rest of the structure.

Also, rubber mounts in the system change the boundary conditions for any beam vibrational resonances so that the system is now somewhat close to a free state, as opposed to a state where the Drive is rigidly clamped to the airframe. This raises beam vibrational mode considerably, and allows us to use a smaller diameter motor rotor shaft, which then offsets the added weight from the rubber mounts.

We are running this Drive right now, and it's working great. It is spinning very true, and vibration free.

The gears and the bearings also look like they'll last forever, and we are adding a second front bearing to the motor to take axial loads, so this shouldn't be a problem either.

One problem we are having is with the thermal performance of the 1512 motor that we are using. I am worried that heat rise with this motor is going to be too high for typical flyers, and we may have to upsize it to a 1515 motor to make it more robust.

One of the benefits of this kind of design is that it is very easy to swap different motors in an out. The Drive itself is going to be rated for 4500 W, so if we get any dramatic new advance in battery technology in the next few years, we can use more powerful motors to take advantage of it, and the drive can remain unchanged.

Brenner ...

Jetdesign

My Feedback: (8)

Brenner, it is awesome to watch and read about your continuing progress. All of your technology seems well thought-out and your explanations are clear and concise. Keep up the good work!

Brenner

Hey Joe,

Thanks for the kind words. I'll see you on the D4 pattern circuit this year.

Brenner ...

Malcolm H

Brenner,

Two scenarios which would concern me regarding motor shaft bending are:

a) A nose over on landing or a hard touchdown causing a blade to contact the ground. (This happened to me on an early Contra competition flight in very gusty windy conditions, only damage was a cracked front prop).

b) Hanger rash damage, taking the model in/out of workshop or car. We have all banged part of a model on something we shouldn't no matter how careful we are.

I'm just slightly concerned that the bullet proof nature of the existing design might be compromised with this design.

Malcolm

serious power

Hi,
This design, as I understand it, eliminates the wear point at the motor shaft/pinion gear interface.

Testing should identify any/most weak points - which can then be addressed.
Brenner,Mike and Andy have not been found wanting in this regard - at all.

Brian

Brenner

Hey Malcolm,

This design still uses a planetary gearset, so if the props are struck during a nose over, or taking a plane in and out of a car or workshop, the Drive should still behave the same, or are you worried about a different kind of failure mode?

Brenner ...

Malcolm H

Hi Brenner,

Of course I'm well aware the drive uses the planetary gearset and you are right I'm not thinking about a torque induced failure but the possibility of a pure bending moment being applied to the motor shaft by striking a prop either near the tip axially as might happen if you banged the prop off something while carrying the model, or during a prop strike when there will be a combined axial load on the prop tip (caused by the aircraft's forward motion) and a torque induced bending moment caused by the rotation of the prop.

And Brian, I'm well aware that Brenner and his team have been superb at identifying and sorting problems with the existing drives and I have no doubt they will do the same with this one, was just trying to make some constructive input.

Malcolm

serious power

Hi Malcolm,
I know that 'you' know
My post above did not address you specifically.

I'd love to see one of these in the flesh.
This has the potential to be yet another significant leap forward in F3A propulsion.

Brian

Brenner

Hey Malcolm,

Ok, I understand what your concern is now.

I agree, this is a potential failure mode, and it's a little difficult to calculate and predict the effects of impacts in system like this that is rubber mounted. It can be done, but I think in our case prototype testing is more time and resource efficient.

Our current thinking is that the rubber mounts are going to go a long way towards absorbing and mitigating the kinds of impacts that you describe, and our design intent is to have enough strength and robustness in the Drive so that mounting system will fail before the Drive does.

We want to start our testing and evaluation with a 5mm shaft because this is the lightest setup, but if shaft bending does prove to be an issue, we have enough design freedom to increase the shaft diameter to 6mm or even 8mm if we have to, but I want to end up with the lightest setup that will do the job.

Brenner ...

pippy

Hi Brenner, the rubber mounting system with the new Inspire is a lot more rigid than the ones you are using, do you see any potential for problem with this? The rubber mount Is a grommet type that goes through the fire wall.