Contra Rotating Propeller Drive for f3a 2m Pattern Planes
06-01-2016, 11:35 AM
#1676
Thread Starter
"The Spin 99 ESC will not work with the 600-09 motor because it is a 14 pole motor. Do not use this ESC. You will need to use a Jeti Mezon ESC with this motor."
Please may I ask why not, re the spin 99? If it's the number of poles, I'd just add that the 99 is quite happy with the 20-pole Pletty Advance 30-10, and as far as I know, with the 28-pole Hackers.
Please may I ask why not, re the spin 99? If it's the number of poles, I'd just add that the 99 is quite happy with the 20-pole Pletty Advance 30-10, and as far as I know, with the 28-pole Hackers.
The problem is actually a combination of too many poles and too much rpm. There are inrunners with lots of poles, but they have low kv's and they spin at low rpm, usually 6000 rpm max.
However, as a motor spins faster, the ESC has to commutate faster, and the speed that it has to commutate at is a function of the number of poles and the motor rpm. So, if you have a lot of poles, and you spin very fast, it is the combination of the two that creates the problem.
In the case of the Pyro-600 motor, it spins at 30,000 rpm, and it has 14 poles, so the commutation frequency is:
30,000*14/60 = 7,000hz
In the case of a Hacker Q80 motor, it spins at 6,000 rpm, and it has 28 poles, so the commutation frequency is:
6,000*28/60 = 2,800hz
Which is less than half the rate required for the Pyro motor.
Brenner ...
Last edited by Brenner; 06-01-2016 at 11:51 AM. Reason: Spelling Mistake ..
06-01-2016, 11:50 AM
#1677
Thread Starter
A quick update on the Hacker A50 8s motor that I am testing.
I started flying this motor over the Memorial day weekend, and I am liking it very much. The power is excellent! It has almost as much power as the Pyro 600 motor, but also with the stump pulling torque of the Pyro 650.
The shaft is 8mm diameter in the rear, and it steps down to 6mm in the front, and it is hollow in the 8mm section to keep the weight down. The motor also comes with two bearings in the rear so it should support axial loads well. Overall, the build quality is excellent.
The thermal performance isn't as good as the 650 motor. It is probably closer to the 600 motor than the 650, but still very acceptable. (at least in my installation ..)
I am a little concerned because there is no hardened thrust washer between the inner race of the rear bearing, and the aluminum rotor fan, which means that the inner race might fret against the aluminum surface of the fan hub.
This isn't a big problem though, and I have ordered some thrust washers from McMaster Carr that I will install.
The only downside that I can see is that the motor is just a little heavy at 355g. This compares with 230g for the 600 motor, and 305g for the 650 motor.
My next step is to try this motor with the new Falcon 23" props. My expectation is that these props will draw about 10% more power, which might make the A50 a very good match.
Brenner ...
I started flying this motor over the Memorial day weekend, and I am liking it very much. The power is excellent! It has almost as much power as the Pyro 600 motor, but also with the stump pulling torque of the Pyro 650.
The shaft is 8mm diameter in the rear, and it steps down to 6mm in the front, and it is hollow in the 8mm section to keep the weight down. The motor also comes with two bearings in the rear so it should support axial loads well. Overall, the build quality is excellent.
The thermal performance isn't as good as the 650 motor. It is probably closer to the 600 motor than the 650, but still very acceptable. (at least in my installation ..)
I am a little concerned because there is no hardened thrust washer between the inner race of the rear bearing, and the aluminum rotor fan, which means that the inner race might fret against the aluminum surface of the fan hub.
This isn't a big problem though, and I have ordered some thrust washers from McMaster Carr that I will install.
The only downside that I can see is that the motor is just a little heavy at 355g. This compares with 230g for the 600 motor, and 305g for the 650 motor.
My next step is to try this motor with the new Falcon 23" props. My expectation is that these props will draw about 10% more power, which might make the A50 a very good match.
Brenner ...
06-01-2016, 04:26 PM
#1679
Hi Brenner
Flipping a bearing has solved the lockup issue. I do wonder if the bearings could be damaged after being tightened and becoming stiff?
The bearings really are loose in the housing. Here is a video to demonstrate http://www.sendspace.com/file/iiso99 I don't think the case will last long as the bearing may rotate in it......
Also, the bearing cap washer is free to move? So it floats outside the bearing outer race, as seen on the video.
I wonder if you should look at the drive? I have PM'd you my email address if it is better to discuss by email?
Andrew
Flipping a bearing has solved the lockup issue. I do wonder if the bearings could be damaged after being tightened and becoming stiff?
The bearings really are loose in the housing. Here is a video to demonstrate http://www.sendspace.com/file/iiso99 I don't think the case will last long as the bearing may rotate in it......
Also, the bearing cap washer is free to move? So it floats outside the bearing outer race, as seen on the video.
I wonder if you should look at the drive? I have PM'd you my email address if it is better to discuss by email?
Andrew
06-01-2016, 04:35 PM
#1680
Thread Starter
Hey Andrew,
Good questions, and excellent video...
When the Drive is assembled, there is a very powerful spring washer that clamps the outer races of the bearings with more than 270kg of force. This prevents the bearings from moving.
The bearing cap washer should push down into a recess in the gearcase bearing bore that will prevent it from sliding around like you are showing. If it doesn't do this, then the bearings aren't seated down far enough.
The user manual has exploded view pictures that will show you all of the parts and how they go together.
When you reassemble the Drive, make sure that you orient the spring washer properly so that it is compressed by the ring gear when the rear hub is bolted on to the gearcase.
Brenner ...
Good questions, and excellent video...
When the Drive is assembled, there is a very powerful spring washer that clamps the outer races of the bearings with more than 270kg of force. This prevents the bearings from moving.
The bearing cap washer should push down into a recess in the gearcase bearing bore that will prevent it from sliding around like you are showing. If it doesn't do this, then the bearings aren't seated down far enough.
The user manual has exploded view pictures that will show you all of the parts and how they go together.
When you reassemble the Drive, make sure that you orient the spring washer properly so that it is compressed by the ring gear when the rear hub is bolted on to the gearcase.
Brenner ...
Last edited by Brenner; 06-01-2016 at 04:37 PM.
06-01-2016, 05:05 PM
#1682
Thread Starter
Andy,
The gearcase bearing bore is sized to be a size on size fit, which means that tolerances will result in either a slight interference fit, or a slight clearance fit.
Your video seems to be showing the latter.
Brenner...
The gearcase bearing bore is sized to be a size on size fit, which means that tolerances will result in either a slight interference fit, or a slight clearance fit.
Your video seems to be showing the latter.
Brenner...
06-18-2016, 08:28 AM
#1683
Thread Starter
There is a new learning that we need to pass on to Contra V4 pilots who are doing a lot of flying with the new F17 finals pattern.
This pattern has a lot of maneuvers that require extended knife edge flight, and what we have seen is that the rubber mounted rear support can move around noticeably when high deflection rudder is used.
This movement isn't a lot in absolute terms, but what it does is cause the rear support to be twisted, which applies a bending moment to the needle bearing in the rear support.
This is a problem, because while needle bearings are capable of supporting large perpendicular loads, they are not so good with bending moments. What happens when a bending moment is applied is that the needles in the bearing get skewed, which applies pressure to the ends of the bearing cage, which can lead to failure of the bearing.
The solution to this is to hard mount the rear support instead of using rubber mounts. Do not change the rubber mounts on the front motor plate. They are working fine. What's needed is a more rigidly mounted rear support plate.
Another possible solution is to use a rubber mounted three point mounting system for the rear support (like the motor plate in front...) instead of the current two point system. This would support bending moments through a full 360 degrees, instead of just in-line with the support, like with the current two point system.
This is only for pilots who are flying F17. There is no issue for pilots flying P17, AMA Masters, and patterns that don't require a lot of rudder authority. (as compared to F17 ..)
Brenner ...
This pattern has a lot of maneuvers that require extended knife edge flight, and what we have seen is that the rubber mounted rear support can move around noticeably when high deflection rudder is used.
This movement isn't a lot in absolute terms, but what it does is cause the rear support to be twisted, which applies a bending moment to the needle bearing in the rear support.
This is a problem, because while needle bearings are capable of supporting large perpendicular loads, they are not so good with bending moments. What happens when a bending moment is applied is that the needles in the bearing get skewed, which applies pressure to the ends of the bearing cage, which can lead to failure of the bearing.
The solution to this is to hard mount the rear support instead of using rubber mounts. Do not change the rubber mounts on the front motor plate. They are working fine. What's needed is a more rigidly mounted rear support plate.
Another possible solution is to use a rubber mounted three point mounting system for the rear support (like the motor plate in front...) instead of the current two point system. This would support bending moments through a full 360 degrees, instead of just in-line with the support, like with the current two point system.
This is only for pilots who are flying F17. There is no issue for pilots flying P17, AMA Masters, and patterns that don't require a lot of rudder authority. (as compared to F17 ..)
Brenner ...
06-19-2016, 10:11 AM
#1684
Thread Starter
Currently, there is a known issue with endplay in the main gearcase bearings. We have been working to develop a fix for this, but before I describe what we have come up with, let me provide a little background.
Originally, during the development of the V4 Drive, we had intended to use C0 clearance rated bearings, and this worked very well during all of our prototype testing.
The bearings that we had specified were ABEC 7, C0 bearings with ceramic balls, and a polymer cage. The ceramic balls and the polymer cage raised the maximum rpm limit considerably, and the C0 rating was intended to minimize bearing endplay in the fully assembled system, which it did quite well.
However, when we purchased a larger batch of these bearings, the bearings that our supplier sent us had considerable differences in the centering of the groove in the inner race, which caused the inner race to either stick up too far, or be recessed too far.
In most applications this probably wouldn't be an issue, but in our application it was an issue because we clamp both the inner and outer races, and if the inner race isn't positioned properly relative to the outer race, the bearing can get preloaded, and jam up.
It turned out that this was a problem only with the batch of bearings that our supplier sent us, but we wanted to be certain that there was no possibility of the bearings being preloaded in any of our assemblies, so what we did was replace this batch of bearings with C3 clearance rated bearings. C3 rated bearings allow for more axial displacement of the inner race relative to the outer race, so any issue with preloading is eliminated.
However, what we were left with is a bearing endplay issue. This bearing endplay doesn't affect the performance of the Drive, because the Drive is designed to "center up" under load, but it is certainly disconcerting, and many customers would like to eliminate it.
So, in the last few weeks we have been working to develop a fix for this problem, both for the Drives that we ship to customers, and for Drives that have already been purchased by customers.
We had originally thought that we could develop a "shim kit", and use a custom combination of shims to take up the endplay with each Drive assembly. This works, but it is difficult to completely eliminate bearing endplay using shims, and there is also a risk that if the system is shimmed too much, the bearings get preloaded again.
We were also concerned about what would happen when a Drive is serviced, and the bearings get flipped, because any particular set of shims will only be valid for one orientation of the bearings.
Instead, what we have decided to do is physically eliminate the play in each bearing by burnishing the inner and outer races using a high speed disk sander that is mounted with a 600 grit emery cloth disk.
What we do is press each side of the bearing against the sanding disk by pressing on the inner race. We do this for both sides of the bearing, and we do it until enough material is removed to eliminate any clearance inside the bearing.
The result is bearings that have zero endplay when the Drive is assembled. There is still a very small amount of endplay that can be felt, but this is due to clearance in the rear support needle bearing. If the rear of the motor is held, there is zero endplay in the system.
We plan to still continue to specify C3 clearance bearings, because these bearings have a larger contact angle, which significantly increases the bearings ability to be robust to axial loads, but we are now shipping all Drives with zero endplay bearings.
For customers that have Drives that still have excessive endplay. It is very possible for existing bearings to be modified in this same way.
What is needed is the following:
1/.. A hard, flat surface. ( I have a granite kitchen counter top which works great for me..)
2/.. A sheet of 600 grit, wet/Dry emory cloth.
3/.. The two main bearings disassembled from the Drive.
The process is as follows:
1/.. The hard flat surface is cleaned of any debris, and the sheet of emory cloth sandpaper is placed on it.
2/.. Place each bearing (in turn..) on the emory cloth sheet, and press on the inner race.
3/.. Push the bearings back and forth on the emory cloth until both the inner and outer races are equally burnished. Do not touch the outer race while you do this.
4/.. Do this for both sides of each bearing.
5/.. Blow any debris away while you are burnishing, and clean each bearing with a paper towel or a rag when you are finished.
6/.. Reassemble the bearings in the Drive, and check for endplay.
7/.. If endplay still exists, repeat the above process.
For customers who don't want to use this process, we can provide zero endplay bearing sets as replacement parts.
Brenner ...
Originally, during the development of the V4 Drive, we had intended to use C0 clearance rated bearings, and this worked very well during all of our prototype testing.
The bearings that we had specified were ABEC 7, C0 bearings with ceramic balls, and a polymer cage. The ceramic balls and the polymer cage raised the maximum rpm limit considerably, and the C0 rating was intended to minimize bearing endplay in the fully assembled system, which it did quite well.
However, when we purchased a larger batch of these bearings, the bearings that our supplier sent us had considerable differences in the centering of the groove in the inner race, which caused the inner race to either stick up too far, or be recessed too far.
In most applications this probably wouldn't be an issue, but in our application it was an issue because we clamp both the inner and outer races, and if the inner race isn't positioned properly relative to the outer race, the bearing can get preloaded, and jam up.
It turned out that this was a problem only with the batch of bearings that our supplier sent us, but we wanted to be certain that there was no possibility of the bearings being preloaded in any of our assemblies, so what we did was replace this batch of bearings with C3 clearance rated bearings. C3 rated bearings allow for more axial displacement of the inner race relative to the outer race, so any issue with preloading is eliminated.
However, what we were left with is a bearing endplay issue. This bearing endplay doesn't affect the performance of the Drive, because the Drive is designed to "center up" under load, but it is certainly disconcerting, and many customers would like to eliminate it.
So, in the last few weeks we have been working to develop a fix for this problem, both for the Drives that we ship to customers, and for Drives that have already been purchased by customers.
We had originally thought that we could develop a "shim kit", and use a custom combination of shims to take up the endplay with each Drive assembly. This works, but it is difficult to completely eliminate bearing endplay using shims, and there is also a risk that if the system is shimmed too much, the bearings get preloaded again.
We were also concerned about what would happen when a Drive is serviced, and the bearings get flipped, because any particular set of shims will only be valid for one orientation of the bearings.
Instead, what we have decided to do is physically eliminate the play in each bearing by burnishing the inner and outer races using a high speed disk sander that is mounted with a 600 grit emery cloth disk.
What we do is press each side of the bearing against the sanding disk by pressing on the inner race. We do this for both sides of the bearing, and we do it until enough material is removed to eliminate any clearance inside the bearing.
The result is bearings that have zero endplay when the Drive is assembled. There is still a very small amount of endplay that can be felt, but this is due to clearance in the rear support needle bearing. If the rear of the motor is held, there is zero endplay in the system.
We plan to still continue to specify C3 clearance bearings, because these bearings have a larger contact angle, which significantly increases the bearings ability to be robust to axial loads, but we are now shipping all Drives with zero endplay bearings.
For customers that have Drives that still have excessive endplay. It is very possible for existing bearings to be modified in this same way.
What is needed is the following:
1/.. A hard, flat surface. ( I have a granite kitchen counter top which works great for me..)
2/.. A sheet of 600 grit, wet/Dry emory cloth.
3/.. The two main bearings disassembled from the Drive.
The process is as follows:
1/.. The hard flat surface is cleaned of any debris, and the sheet of emory cloth sandpaper is placed on it.
2/.. Place each bearing (in turn..) on the emory cloth sheet, and press on the inner race.
3/.. Push the bearings back and forth on the emory cloth until both the inner and outer races are equally burnished. Do not touch the outer race while you do this.
4/.. Do this for both sides of each bearing.
5/.. Blow any debris away while you are burnishing, and clean each bearing with a paper towel or a rag when you are finished.
6/.. Reassemble the bearings in the Drive, and check for endplay.
7/.. If endplay still exists, repeat the above process.
For customers who don't want to use this process, we can provide zero endplay bearing sets as replacement parts.
Brenner ...
Last edited by Brenner; 06-19-2016 at 10:13 AM.
06-20-2016, 09:54 AM
#1686
Thread Starter
Hey Robert,
Looks good!
We are thinking of switching to a hard mounted support for all new Drives that we ship, because hard mounted works for all classes of pilots.
Brenner ...
Looks good!
We are thinking of switching to a hard mounted support for all new Drives that we ship, because hard mounted works for all classes of pilots.
Brenner ...
06-20-2016, 11:19 AM
#1687
Thanks Brenner. I did notice a couple things after changing to a hard mount rear support. The model has an easy time in my opinion on exiting maneuvers. Flying before with the soft mount, I always had to work a little more to position the wing to make sure the entry and exit were clean, with the hard mount it is much easier. I also noticed that the rudder is much more effective. I think the soft mount gave it a type of dampening effect, so if you hard mount it, prepare to add a little more expo. Knife edge did not change, so that was a plus. Will provide more feedback as I get more flights, but so far so good. Another plus, I saved an additional 9 grams.
Last edited by rgreen24; 06-20-2016 at 11:22 AM.
06-21-2016, 11:07 AM
#1689
I had always thought that the original mounting of the needle bearing in a rubber grommet was a good idea in that it would allow the bearing axis to self-align with the motor shaft. Perhaps when we went to the captured bearing mount, this alignment freedom, together with the motor mount movement, created the "F" problem noted.
What I'm going to try, unless Brenner thinks it's a bad idea, is to swap the needle bearing mounts with the "stiff" bud mounts and go back to the grommet mounted needle bearing. I'll add a bit of flexible adhesive to keep the needle bearing from walking axially out of the grommet.
I've probably said this before, but I appreciate the candor with which you come forward with problems (and solutions) when they are detected. There are so many companies who will only admit to problems once forced to by government/legal actions or who try to sneak in the fix with the next generation product. Yours is the kind of company that I want to buy from!
Regards, Dan
What I'm going to try, unless Brenner thinks it's a bad idea, is to swap the needle bearing mounts with the "stiff" bud mounts and go back to the grommet mounted needle bearing. I'll add a bit of flexible adhesive to keep the needle bearing from walking axially out of the grommet.
I've probably said this before, but I appreciate the candor with which you come forward with problems (and solutions) when they are detected. There are so many companies who will only admit to problems once forced to by government/legal actions or who try to sneak in the fix with the next generation product. Yours is the kind of company that I want to buy from!
Regards, Dan
06-21-2016, 11:23 AM
#1690
Thread Starter
Hey Dan,
Stiff grommets are fine on the rear support. However, do not use them on the front motor plate.
The only other rear support configuration we have tested is with soft grommets and we know that high rate rudder usage in F17 will create damaging bending moments in the needle bearing if endcaps are used, and we know that high rate rudder will also probably walk the bearing out of a rubber center grommet if it's given a chance.
Our current recommendation is to use the plastic endcaps, and hard mount the rear carbon fiber support plate. This is what I am flying right now, and it works well.
Also, thanks for the kind words. We know that the guys who fly both the V3 and the V4 Drives, are pretty savvy technically, and we are keen on listening to them, and implementing whatever changes are needed to make the best Drives possible.
Brenner ..
Stiff grommets are fine on the rear support. However, do not use them on the front motor plate.
The only other rear support configuration we have tested is with soft grommets and we know that high rate rudder usage in F17 will create damaging bending moments in the needle bearing if endcaps are used, and we know that high rate rudder will also probably walk the bearing out of a rubber center grommet if it's given a chance.
Our current recommendation is to use the plastic endcaps, and hard mount the rear carbon fiber support plate. This is what I am flying right now, and it works well.
Also, thanks for the kind words. We know that the guys who fly both the V3 and the V4 Drives, are pretty savvy technically, and we are keen on listening to them, and implementing whatever changes are needed to make the best Drives possible.
Brenner ..
06-21-2016, 03:22 PM
#1691
My Feedback: (41)
I just listed some new sizes from Falcon
We now have 14 Falcon CRP props in stock.
Some are geared for other Contra units. The feedback on these props is very positive so far.
http://www.f3aunlimited.com/contra/c.../falcon-contra
Mike Mueller
We now have 14 Falcon CRP props in stock.
Some are geared for other Contra units. The feedback on these props is very positive so far.
http://www.f3aunlimited.com/contra/c.../falcon-contra
Mike Mueller
06-21-2016, 04:34 PM
#1692
Join Date: Feb 2003
Location: BODOE, NORWAY
Posts: 181
Likes: 0
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I just listed some new sizes from Falcon
We now have 14 Falcon CRP props in stock.
Some are geared for other Contra units. The feedback on these props is very positive so far.
http://www.f3aunlimited.com/contra/c.../falcon-contra
Mike Mueller
We now have 14 Falcon CRP props in stock.
Some are geared for other Contra units. The feedback on these props is very positive so far.
http://www.f3aunlimited.com/contra/c.../falcon-contra
Mike Mueller
Last edited by Mavpro; 06-22-2016 at 12:33 AM.
07-01-2016, 10:44 AM
#1693
Thread Starter
Some new learnings:
Recently, I have been experimenting with some of the new Falcon 23" props, and since they are longer than the 22" props, and my landing gear isn't also proportionally longer, I had one or two prop strikes.
Prop strikes typically aren't a big deal for the Contra Driove, (it can be a big deal for the props though ..) but in this case what happened was that subsequent flights resulted in a very noticeable increase in noise coming from my Drive. I heard the same thing on the ground as well, and I had a noticeable increase in fuselage vibration too. I was pissed, because I assumed that the prop strike had damaged the Drive is some way, but when I took it apart, there was nothing wrong.
I was stumped, so I reassembled everything and put in another flight, and low and behold, the problem was fixed. My Drive was nice and quiet again.
Everything was fine until I had another prop strike, and then I had the same horrible noise on subsequent flights.
This time I spent a little more time investigating, and what I found was that the holes in the fuselage mounts for my rear support were oversize, which allowed the rear support to shift when I had a prop strike. This preloaded the rear support needle bearing against the motor shaft, which created a conductive path from the motor to my fuselage for noise and vibration. My fuselage then acted like a megaphone and amplified the sound accordingly.
The take-aways for all this are the following:
1/.. It is very important to install the Drive, the fuselage plate, and the front motor plate first, before installing the rear support. The rear support mounting holes then need to be drilled so that the rear support is appropriately aligned with the installed Drive.
2/.. Drive down-thrust must "not" be adjusted by shifting the rear support and preloading the rubber grommets on the front motor plate . Instead, the grommets on the front motor plate should be shimmed, and the mounting holes for the rear support relocated accordingly.
3/.. The mounting holes for the rear support must not be oversize, because this will allow the rear support to shift if the Drive experiences a prop strike.
One final application of all this is that it is now easy for me to know when the Drive is seeing gyroscopic forces due to the spinning motor rotor, because when these forces are present, I can hear the same noise due to the rear support being pushed against the motor shaft.
Right now I hear this noise only in the F17 pattern during the reverse knife edge top hat, and the knife edge loop.
Brenner ...
Recently, I have been experimenting with some of the new Falcon 23" props, and since they are longer than the 22" props, and my landing gear isn't also proportionally longer, I had one or two prop strikes.
Prop strikes typically aren't a big deal for the Contra Driove, (it can be a big deal for the props though ..) but in this case what happened was that subsequent flights resulted in a very noticeable increase in noise coming from my Drive. I heard the same thing on the ground as well, and I had a noticeable increase in fuselage vibration too. I was pissed, because I assumed that the prop strike had damaged the Drive is some way, but when I took it apart, there was nothing wrong.
I was stumped, so I reassembled everything and put in another flight, and low and behold, the problem was fixed. My Drive was nice and quiet again.
Everything was fine until I had another prop strike, and then I had the same horrible noise on subsequent flights.
This time I spent a little more time investigating, and what I found was that the holes in the fuselage mounts for my rear support were oversize, which allowed the rear support to shift when I had a prop strike. This preloaded the rear support needle bearing against the motor shaft, which created a conductive path from the motor to my fuselage for noise and vibration. My fuselage then acted like a megaphone and amplified the sound accordingly.
The take-aways for all this are the following:
1/.. It is very important to install the Drive, the fuselage plate, and the front motor plate first, before installing the rear support. The rear support mounting holes then need to be drilled so that the rear support is appropriately aligned with the installed Drive.
2/.. Drive down-thrust must "not" be adjusted by shifting the rear support and preloading the rubber grommets on the front motor plate . Instead, the grommets on the front motor plate should be shimmed, and the mounting holes for the rear support relocated accordingly.
3/.. The mounting holes for the rear support must not be oversize, because this will allow the rear support to shift if the Drive experiences a prop strike.
One final application of all this is that it is now easy for me to know when the Drive is seeing gyroscopic forces due to the spinning motor rotor, because when these forces are present, I can hear the same noise due to the rear support being pushed against the motor shaft.
Right now I hear this noise only in the F17 pattern during the reverse knife edge top hat, and the knife edge loop.
Brenner ...
07-04-2016, 07:40 PM
#1694
Join Date: Aug 2005
Location: Sydney, AUSTRALIA
Posts: 1,341
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Some new learnings:
Recently, I have been experimenting with some of the new Falcon 23" props, and since they are longer than the 22" props, and my landing gear isn't also proportionally longer, I had one or two prop strikes.
Prop strikes typically aren't a big deal for the Contra Driove, (it can be a big deal for the props though ..) but in this case what happened was that subsequent flights resulted in a very noticeable increase in noise coming from my Drive. I heard the same thing on the ground as well, and I had a noticeable increase in fuselage vibration too. I was pissed, because I assumed that the prop strike had damaged the Drive is some way, but when I took it apart, there was nothing wrong.
I was stumped, so I reassembled everything and put in another flight, and low and behold, the problem was fixed. My Drive was nice and quiet again.
Everything was fine until I had another prop strike, and then I had the same horrible noise on subsequent flights.
This time I spent a little more time investigating, and what I found was that the holes in the fuselage mounts for my rear support were oversize, which allowed the rear support to shift when I had a prop strike. This preloaded the rear support needle bearing against the motor shaft, which created a conductive path from the motor to my fuselage for noise and vibration. My fuselage then acted like a megaphone and amplified the sound accordingly.
The take-aways for all this are the following:
1/.. It is very important to install the Drive, the fuselage plate, and the front motor plate first, before installing the rear support. The rear support mounting holes then need to be drilled so that the rear support is appropriately aligned with the installed Drive.
2/.. Drive down-thrust must "not" be adjusted by shifting the rear support and preloading the rubber grommets on the front motor plate . Instead, the grommets on the front motor plate should be shimmed, and the mounting holes for the rear support relocated accordingly.
3/.. The mounting holes for the rear support must not be oversize, because this will allow the rear support to shift if the Drive experiences a prop strike.
One final application of all this is that it is now easy for me to know when the Drive is seeing gyroscopic forces due to the spinning motor rotor, because when these forces are present, I can hear the same noise due to the rear support being pushed against the motor shaft.
Right now I hear this noise only in the F17 pattern during the reverse knife edge top hat, and the knife edge loop.
Brenner ...
Recently, I have been experimenting with some of the new Falcon 23" props, and since they are longer than the 22" props, and my landing gear isn't also proportionally longer, I had one or two prop strikes.
Prop strikes typically aren't a big deal for the Contra Driove, (it can be a big deal for the props though ..) but in this case what happened was that subsequent flights resulted in a very noticeable increase in noise coming from my Drive. I heard the same thing on the ground as well, and I had a noticeable increase in fuselage vibration too. I was pissed, because I assumed that the prop strike had damaged the Drive is some way, but when I took it apart, there was nothing wrong.
I was stumped, so I reassembled everything and put in another flight, and low and behold, the problem was fixed. My Drive was nice and quiet again.
Everything was fine until I had another prop strike, and then I had the same horrible noise on subsequent flights.
This time I spent a little more time investigating, and what I found was that the holes in the fuselage mounts for my rear support were oversize, which allowed the rear support to shift when I had a prop strike. This preloaded the rear support needle bearing against the motor shaft, which created a conductive path from the motor to my fuselage for noise and vibration. My fuselage then acted like a megaphone and amplified the sound accordingly.
The take-aways for all this are the following:
1/.. It is very important to install the Drive, the fuselage plate, and the front motor plate first, before installing the rear support. The rear support mounting holes then need to be drilled so that the rear support is appropriately aligned with the installed Drive.
2/.. Drive down-thrust must "not" be adjusted by shifting the rear support and preloading the rubber grommets on the front motor plate . Instead, the grommets on the front motor plate should be shimmed, and the mounting holes for the rear support relocated accordingly.
3/.. The mounting holes for the rear support must not be oversize, because this will allow the rear support to shift if the Drive experiences a prop strike.
One final application of all this is that it is now easy for me to know when the Drive is seeing gyroscopic forces due to the spinning motor rotor, because when these forces are present, I can hear the same noise due to the rear support being pushed against the motor shaft.
Right now I hear this noise only in the F17 pattern during the reverse knife edge top hat, and the knife edge loop.
Brenner ...
This may be stating the obvious but perhaps you could just fit longer gear to your model?
It's funny how only a few years ago a 20" prop was seen as big. Now we're at 23".
Cheers,
Jason.
07-04-2016, 11:25 PM
#1695
Thread Starter
Hey Jason,
Yes, I agree... I have actually been using the longest gear that I could find, but the longest gear was only good for 22" props.
However, about a week ago Mike Mueller for f3aunlimited.com started stocking gear from Falcon that is 12mm longer, and I have been using them with 100% success rate.
Brenner ...
PS-> I have also been concentrating a little more when I land, which has also helped...
Yes, I agree... I have actually been using the longest gear that I could find, but the longest gear was only good for 22" props.
However, about a week ago Mike Mueller for f3aunlimited.com started stocking gear from Falcon that is 12mm longer, and I have been using them with 100% success rate.
Brenner ...
PS-> I have also been concentrating a little more when I land, which has also helped...
10-02-2016, 11:04 AM
#1700
Join Date: Jul 2005
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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 so 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
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