Hi Dennis - Might you include a third alternative, a supplemental bearing opposite the mount end of the motor?  The photo shows the layout.  That airplane is up to about 200 flights, with no motor bearing issues.  The extra bearing mount shown had a bearing with a mounting lip held to the plate with JB weld.  That joint failed at about 75 flights, and has been replaced with a mount which clamps the bearing lip in place with a washer bolted to the mount plate.  This indicates that the supplemental bearing is taking sufficient load to protect the internal motor bearings.  My observation is that the front mounts seem to get about 200 flights and then require a full bearing replacement.

Like Tom I have always used a supplemental bearing to "spread" the forces exerted upon the motor shaft. Over the years I have experimented with both front and rear mounts. In each case adding the supplemental bearing seemed to be the answer to reducing internal motor bearing wear. The only difference is that I prefer the rear mount system with a bolt on prop shaft so my bearing is in the back.

Funny, I was just about say I use front, because it's easier   But then I will also keep using Velcro for my battery mounts.

I'm a Paul disciple. What can I say.

Not really much difference in design I suppose, one is just a few inches ahead if the other.  Front mount may add some cooling challenges.  Keeping the prop and motor can properly balanced goes a long way to reduce stress.

I don't get the idea of adding a 3rd bearing.  I know a lot of folks swear by it, but can any body think of an example of a mechanical device that uses 3 ball bearings on one (straight) ridged shaft?   I think it would be a nightmare to get them all aligned without adding any radial loading on the other bearings.

Paul

Front mount.  I have no issues front mounting them. On my OTS Jamison Special, the motor is rear mounted because it replaced an OS 35FP!

Just curious.

I am working on a new set of conversion kits.  Latest thinking includes parts for that enable builder to use either front mount or rear mount and I am writing instruction manuals for both versions.   Question is what mounting systems are you currently using and which would you use if BOTH were available?

Why do you prefer that method (front mount or rear)? What are the biggest obstacles to you using that mounting system?

...and THANK YOU in advance for sharing your thoughts...

Hi Dennis!

When Pat and I were just starting to talk about an electric stunter in the spring of 2005 he brought an electric r/c model fuselage out to one of our contests to show me how the motor started. (now understand that Pat has more experience in more types of model aviation than the next fifty people standing beside you at any contest!) He connected the battery - the esc initialized - and then ............ wait for it ......wait for it.........Blam!!! Bling!!!
KaPow!!!!! - the nose flew off the model.  The throttle had been advance too quickly! 

Electric motors have ALL of their torque available at ZERO RPM's !!!

Think about that for a minute vs an IC engine.

Now while we all use soft start and this should not ever happen to us, it certainly made quite impression on me. It was clear that there is very little structure at the tip of the nose as compared to a couple of inches behind it. As I was designing SHOCKWAVE it also became clear that I did not want even more heavy structure that far forward of the CofG. Using a rear mount makes the nose lighter, is easier to implement, is massively stronger and makes servicing easier.



Just a side note-mild rant: IMHO it seems to me that over the last ten years there has been a race for the bottom of the swimming pool of quality by some who fly electric powered control line models. IE: Pay as little as you can for low quality components then try to make up for it and hope for the best. I still have and can use the original motor from SHOCKWAVE with the original bearings rear mounted to-boot. There is no reason to not rear mount a motor unless you are buying junk. 

Purchase a good motor with THREE 3!!! bearings and most of your problems are done with. We do not use our motors in the same way they are used  in any other application. (higher rpm, higher G loads, spinners a papers width from the nose ring, confined cowls). Any model is worth more than difference in price from low quality to higher quality components.

Kim.

my first motor was an emax 2826 wich i found nice but the bearings were not very good  this was rear mounted so as an exercise i bought some beter quality bearings  the i machined out the rear to take 2 bearings close together and along with the front one i glued them in with high quility bearing fit  then to stop the can whip i wound on two layers of  carbon toes  the machinend them down on my lathe  he presto a nice smooth running motor  for not much dosh i enjoyed doing this  it is still rear mounted but i have used an out rigger bearing behind the prop driver  i have a mvvs 950 that goes very well still afrte two years running that needs none of the above so pay your money and make your choise    roy cherry 

The only bearing problem I've ever had since I began flying electric models (and that was in 2005) was when using a rear mount. The bearing didn't fail, but the oscillating motion of the cantilevered spinning mass in front of the mount apparently "coned out" the bearing mount in my AXI 2826-10, three bearing motor and allowed the rear bearing to spin. It created an awful noise... Almost as annoying as a glow engined model! I changed to a front mount system and have had zero problems ever since. Several of us on the East Coast fly with front mounted motors and none of us has had a bearing issue.  So, no matter what anyone says, it's front mounting for me!

Bob Hunt

Thank you for all the feedback.  Each mounting system has its advantages & offsets.  Most of my airplanes are rear mount, but last year’s “Riki” used a front mount system.  That came in handy as I tried (so far) 4 different motors in it – front mounts can be friendlier to that.  Part of the reason I asked this question is that while most all of the motors we use can be reversed, I believe some of the more popular motors are really designed to be front mounted, with the rear mount option an afterthought…

Here are a couple pictures of what I am working on; conversion kits for the Brodak Legacy and Legacy 40. Either kit will make it possible to use a front mounted motor or a rear mounted motor.  These pix are of the front mount system.

As Kim D mentioned there is a LOT of torque & power in play.  We need to harness that power and get it distributed into the fuselage structure.  Like many modern airplanes both Legacy’s are designed with filler blocks between the front of the fuselage sides and the nose ring; great for carving, not so great for mounting a motor – which is where Bob H’s comment comes into play!  Firewall style mounts also need some different efforts to assure alignment – I got an off-line comment expressing this concern.  Because it is a conversion kit it needs to be made to accommodate kit structure.  Of course it should also be easy to build with a minimum of special requirements – I use Titebond 2 for most of the construction.
 
The front mount system uses a ¼” thick ply motor mount that distributes its loading into a 1/8” ply torque box which is designed to be aligned with the top & front edges of the fuselage side.  The torque box also lets the motor be cantilevered about ½” ahead of the front edge of the fuselage.  After building the box the next step is to add some balsa spacers to the front and install the nose ring.  The nose ring is aligned directly to the motor shaft and sets the position for spacers on the sides that take the place of the nose blocks. BTW, I made the nose ring extra wide so it can be carved off at a severe angle (in plan view) to mate with the fuselage without resorting to filler Next the top block is installed and overhangs the sides of the torque box by at least the thickness of the fuselage sides on either side.  Finally, the “F1” bulkhead is installed to cap the back end of the torque box.  This also has a shoulder to align it to the top of the fuselage.