Henning

I flew my Naruke Ascent for the first time this weekend with the Brenner V4 drive. This is the the third motor set-up in this model. First Pletty Advance and then the OS belt drive. Both works well but the Contra took the model to another level flying the F17 schedule. The constant speed and the breaking just makes the manoeuvres look less stressed. I got more time to prepare for the next manoeuvre. The torque and power of the Pyro 600 with Mejzlik 22x20F and 22x22R are very good.


After gaining some knowledge with rubber damping the OS belt drive I decided to design my own motor mount for the Contra drive. One of the main motivation for designing my own was due to the “issues” that has been reported with the rear support bearing and twisting in knife edge manoeuvres in the F17 schedule. My mount eliminates that problem. The pictures explains it better than me.


The firewall is of wood and is a laminate of 0,8mm plywood on both sides with 2mm balsa in the middel. It is lamented with epoxy and heated to 60+ degrees C during curing for extra strength. The front dampers are D10 by H8 mm 60 shore and the rear are D8 by H8 mm 55 shore. I am using fiberglass instead of carbon as it dampens vibrations better. The 4 spacers which makes the whole difference to this month are of aluminium with M3 threads inside and are from a camera drone supplier.


The sound level from this set up is really low in the air and it is the noise from the propellers that can be heard and not the gears.


It is one concern that i have and that is the play in the rear support roller bearing. Is it by design that it is so loose? Will I run into any issues if i replace the bearing with one that fits the motor axel?


Regards,
Henning

Brenner

Hey Henning,

You should have no problem replacing the rear needle bearing with a more traditional bearing. The motor rotor shaft is through hardened to 62RC, so there will be no fretting issues between the shaft and the inner race of a bearing. We are testing a bearing like this right now.

How heavy is your system?

Brenner ...

Henning

Hi Brenner,


I doble posted. the #1700 includes the pictures. It adds 70 grams to the motor + the firewall.


Including 8 rubber dampers, 3 fiber glass plates, the supporting rear bearing with plastic mount the 4 alu standoffs, bolts and alu nuts.


The standoffs are from Aerial Pixels.


https://aerialpixels.com/product-category/tools-hardware/metric-standoffs/?filter_type_=hex&filter_length=60mm



Br,
Henning

Brenner

Hey Henning,

By the way, the issues due to twisting of the rear support have been identified as being due to the natural rubber grommets that were shipped with the Budd Mounts. These grommets have a "linear" stiffness, and the material itself doesn't have very much internal damping. They are very much like using springs without any damping to limit travel.

What we have found is that replacing these natural rubber grommets with the blue vibration isolators from E-A-R Composite Specialties solves all of these problems.

This is because these "blue isolators have much more internal damping, and their spring compliance is "non-linear". The internal damping eliminates any displacement of the Drive as is accelerates through its first natural frequency, and the grommet spring stiffness gets progressively stiffer as the mount starts to move, which limits displacement.

We are currently running with these blue isolators on both the front motor plate and the rear support plate, and the system works well.

I practice the F17 schedule regularly, and I am having no issues. My motor noise doesn't significantly increase when I fly the corners of the inverted top hat, and my Allure tracks through these corners very cleanly, even with large amounts of rudder deflection.

Brenner ...

Brenner

Hey Henning,

Your idea to replace the needle bearing with a regular bearing is a good one. We are going start shipping Drives like this in the near future.

What we are trying to do now is find a bearing that will work with the existing plastic bearing retainer. If we can't do this we will just redesign the bearing retainer to use a clamp plate and a flanged bearing

Brenner ...

Henning

Hi Brenner,

Do you remember the dimensions of the needle bearing currently supplied for the back support? When selecting a replacement ball bearing are there any types to avoid?

Thanks
Henning

Brenner

Hey Henning,

The bearing is a 6x10x8 needle bearing. The loads are low, so pretty much any bearing will work. My recommendation is for a C0 rated bearing to make it nice and tight.

I would also use a shielded bearing as well. I think that the rpms are too high for any kind of contact seal, and all bearings in this size will be rated for more than 30,000 rpm.

Brenner ...

Henning

Thanks,

6x10x3 is a standard dimension and common in RC Cars. One bearing + a 5 mm spacer or two bearings with a 2 mm spacer should fit in the plastic bearing retainer.

Br,
Henning

Henning

Hi,


I changed the needle back support bearing to two high quality 6x10x3 mm ball bearings + a spacer to fill the gap in the plastic case. The spacer I used is a centre ring from an APC propeller. The spacer is 9.5D x2.5 mm and with one round of plastic tape it fits perfectly. The fibre glass plate I am using is 2 mm so this adds up to a perfect fit. After installation i have zero play in the back support.


Test flight hopefully tomorrow.




Br,
Henning

Brenner

Looks good... It should work well.

Henning

Hi,


I flew 1 round P17 and 6 F17 today. The change from the supplied sloppy needle bearing to two tight ball bearings had two positive effects. The plane rolls more axial and the noise level is reduced.


The next to try is mould some air inlets that directs the air to the front of the motor where it is at its hottest. I will also cut a new front mounting plate in aluminium to replace the current one I cut in fibre glass. The aluminium plate will act as a heat sink for the motor.



Br,
Henning

Henning

With proper ducting of cooling air to the motor the temperature went down from “too hot to touch after a flight” to below body temperature.

I created two plugs of foam and covered them with Oracover. The plugs where then coated with wax before adding fibre glass and carbon fibre. The foam and the Oracover where pealed out after curing. Without any trimming and sanding the air ducts came out at 3-4 grams each.


Br,
Henning

Brenner

Hey Henning,

Great Work! Below body temperature is amazing for a motor that generates as much power as this one, and is so small.

Although, "too hot to touch", was probably perfectly fine as well. Humans usually find temperatures above 60C "too hot to touch", and this motor can easily run with case temperatures into the 80's. It's helpful to remember that the magnets in the rotor are rated for 150C, and the motor windings are rated for 300C. Also, we replace the rear bearing with a bearing that has grease that's rated for 250C.

This is a motor that can run quite a bit hotter than what we pattern flyers are used to.

Something that you have probably helped a little more is your ESC. The ESC can actually get very hot when running with this motor if it doesn't have enough airflow. However, I notice that you've located it directly underneath the motor case so the motor fan blows directly over the heat sink fins. This will help a lot to keep it cool, even without your new vents.

Brenner ...

Henning

Thanks Brenner!


The ESC is located just behind a air inlet at the front so it has got cooling from two directions. I am using the Mezon 95 Opto light. The temperature of the ESC with the Pyro is a bit higher than when I used the Pletty Advance. From the sound level the ESC is more happy with the Pyro motor. It is dead quiet. When used with the Advance I get a lot of frequency noise from the motor. It is like the motor amplifies the frequencies like a loud speaker.


I have started to focus a bit more on the cooling of motors and ESC as I have had some issues in the past with overheating ESCs and motors.


The picture was taken while the paint was still wet and reason for the black and flat colours.



Br,
Henning

Brenner

Hey Henning,

With your setup your Motor and your ESC should run very cool.

It's likely that the ESC seems quieter because it has to commutate the Pyro motor at close to 7khz, whereas with the Advance it is probably closer 1.5khz, which is right in the middle of the range that human ears are most sensitive to.

Brenner ...

ltc

My Feedback: (3)

Is there a reason why the Advance needs such a low (1.5KHz) PWM?
I had assumed 8KHz PWM for this motor.

Brenner

Hey Henning,

I am not referring to PWM frequency. I am talking about the frequency that the controller has to use to change the magnet field fast enough to keep up with the magnets in the motor rotating past the motor winding.

If a motor spins at 30,000 rpm, and it has 14 poles, then this commutation frequency is: 30,000*14/60 = 7,000 hz, or 7khz.

This why the PWM frequency needs to be set at 16khz when the ESC is driving the Pyro 600 motor.

Brenner ...

PeterP

Are these type and size of bearing capable of handling the axial loads which could be generated in some maneuvers.

Henning

Hi Peter,


The bearings do not absorb much axial load as most forces are transferred by the standoffs to the back support. How long the bearings will last I do not know. I have only approx. 100 flights to now on them with most of them being F17




Br,
Henning

Brenner

The bearings should last forever.

The only failure mode that you need to be concerned about is fretting of the motor rotor shaft, and this is unlikely because the shaft has been hardened to 60RC.

Brenner ...

PeterP

Hi All,

I recently experienced a problem with my Neu motor which resulted in the ESC almost catching fire in my model during flight. I landed without power and realised how lucky I was when I removed the canopy. Prior to this flight the model has be performing faultlessly without any sign of an impending problem.

I removed the power unit from the model and established the Brenner V3 contra drive was in perfect working order. The ESC was obviously toasted (big time) and the NEU motor seemed a little difficult to turn but would spin. I pulled the motor apart and checked the windings,stator, bearings and nothing obvious stood out. Check to make sure the windings had not shorted to the case and also checked that the windings had not gone open circuit.

At this stage I was not sure if the ESC failed or my NEU was in fault. I had an old ESC laying about so I decided (Stupidly) to see if the motor would run as it seemed OK from what I could tell. Anyway I connected power ESC armed up and as soon as I advanced the throttle the motor chugged for a couple of seconds and the ESC toasted itself.

Obviously the motor has a big issue and it sits in the bottom of my trash can. Anyone experienced this before - Considering the Hacker C54 now - once bitten twice shy.

underdw

My Feedback: (2)

Hi Peter,
I had a similar experience. I had noticed increasing energy consumption during flights, but shrugged it off to windy conditions.
Then I went dead stick, and as I flew directly at myself hoping to make the runway, I saw flames through the chin cowl! The ESC was a lump of charcoal, but fortunately I had it mounted away from the fuse, so it didn't do more than smoke-damage the plane. I can't remember what the motor looked or felt like, but I sent it to Neu and they diagnosed de-magnetization. This is indicative of high temperature in the motor. I do a lot of baffling etc, so not sure what else I could/can do to keep it cool. It's probably a snowball effect: heat causes some demag, which results in more heat, etc. Neu gave me a good deal on replacement and I have hundreds of flights on 2 contra/Neu units without additional issue (of course, a single person's experience proves nothing).
Dan

Anthony-RCU

My Feedback: (2)

I have seen a Neu slip the stator which can cause a similar issue and destroy the ESC. In my case it was caused by a too aggressive break ramp setting causing the motor to decelerate too quickly. Being in the US service from Neu was pretty good.Otherwise I liked them.

Henning

Hi,


My last update to the motor mount has been to cut a front mounting plate out of aluminium to replace the old one made of fiber glass. The plate added 4 grams over the old one but with the increased cooling it should be worth it. The plate is cut from 2mm thick 5xxx alu alloy. 1.5 mm is probably strong enough but 2 mm was what I had laying around. I will add some Thermal paste used for computers between the motor and the alu plate to optimise heat transfer.


I donīt holt an Auto Cad licence any more so my hand drawing will have to do if some one would like to copy it.




Br,
Henning

Brenner

Hey Henning,

Your plate and mount looks good.

We are going to build this mount and test it as well. According to my calculations it will probably add about 30g to the system if we use aluminum rods, but even with this added weight the complete system will still be extremely light.

We are are going to try three rods instead of four so that can reuse the motor mount bolts to hold the rods. We will combine this with a ball bearing rear support, and reuse the EAR Specialties grommets, except that we will replace the plastic spacers in the grommets with aluminum spacers.

This should result in a system that keeps the rear support bearing in perfect alignment with the motor, and provides a firm, but fully isolated mount.

Brenner ...