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SpEEdyBL
08-12-2007, 04:11 AM
As you may have heard, I mentioned earlier that I was going to test the Feigao 8xl against the Novak HV4.5 System. Well, things didn’t go to the best of my luck. Although I managed to prep my Ofna MBX R2 for a brushless system and battery quite easily, it all went down hill from there. My Novak HV4.5 ran fine in the buggy with nine and eleven tooth pinions at first, but every two to five minutes consistently, a tire would come of a rim or an outdrive that gets secured by a set-screw would come loose. I never got to take proper temp readings because continuous runs were to short.
The next thing I knew, the motor shaft snaps off as if it were nothing. This was at the very beginning of the 3rd charge of the pack 5000mah 4s pack I was using. I touched the throttle once, the vehicle moved about two feet and the motor was suddenly free spinning. The motor mount that I made out of a spare 3.5mm thick chassis I admit was not as sturdy as it could be, but it wasn’t wobbly enough that the pinion gear would skip across the spur. It took a bit of muscle ot wobble it at all really.
Now that I could no longer run my HV4.5 motor, I decided run my 8xl/MM combo before placing an order for a replacement rotor on Towerhobbies. I mean, something else might break. Naw, really? After about 7 minutes of running geared 20/51 (really high btw FDR ~ 8:1) both motor and esc were above 190F and many of the teeth of both the front and rear STEEL bevel gears had crumbled to bits! Not only that, but when I checked the motor, the rear endbell was loose. I didn’t even think it was screwed on all the way to begin with. In fact, when I opened the motor up out of curiosity, I found that the endbell could not have been screwed on all the way because the length of the shims added to the length of the rotor was shorter than the internal length of the can! Of course I should mention that the rotor may have been defective to begin with and before I start, just to give you an idea of how cheap Feigao motors are, the 45mm xl rotor was made out of one 30mm long segment, and one 15mm segment side by side. The rotor I had was defective because the two segments were not even touching! They were about 1mm apart, which caused the poor fit inside the can. It appeared as if they were touching at one point, because it could be seen where the broken glue joint that held them together had lined up, but it doesn’t explain why the motor wasn’t screwed on all the way to begin with.
My bad luck doesn’t end here. In fact I’m about half way through so you can stop reading incase you are already overwhelmed. Lets take a look at my shopping list now. A new rotor and new bevel gears of course, but also a pinion gear that would fit directly on a 1/8” shaft (without a 5mm to 1/8” bore reducer, which was needed for the other pinions.) Once my orders came in the mail, I went out to try the HV4.5 again with the new 12 tooth pinion gear. The new bevel gears were installed and this time I put spacers on the bevel pinion for a better mesh in the gearboxes. Guess what. Two minutes into the run, while the vehicle was moving at full speed, the pinion gear pops off and the car goes flying into a curb. Only the bumper broke, but I lost the gear. What now? Now I still have my ll tooth pinion gear. I tried to run that. Finally some luck, but still not lucky enough. After two esc thermals and one motor thermal over the course of a 24 minute run, (I was fairly light on the throttle, which also may have contributed to the high temps and I wasn’t running the included heat sink on the motor) an outdrive falls off; a different one than before! Just as I was going to get my first full run! My pack had about 1000 mah left in it! I’ve gotta say, that really pissed me off. You want to hear the end of the story? The next run after that, I go to a giant parking lot w/ no bumps and the motor shaft snaps off once again less than 5 min into the run. And for the sake of complaining, while I desperately needed to have heavier shock oil in the in front shocks than in the rear . The bottle labeled 80wt that I bought had thinner oil than another bottle with 55 wt. Same brand and everything. It just goes to show how this isn’t totally my fault! Now I can rant about how unlucky I am but you get the idea. Also, you may be wondering why i didn't use thread lock. I'm not lucky with that either.

chilledoutuk
08-12-2007, 11:36 AM
Wow you have had a bad time with this setup but to be honest i would send both those rotors back to novak they need to learn that you need 5mm shafts at least on these high power systems.

secondly I would pickup a decent neu motor or maybe a lehner motor for your car feigao motors are good for proof of concept setups but there built like they cost (cheaply).

I strongly recomend one of mikes motor mounts i think there may be a flec problem between your spur and motor that is causing the mesh to bind and forcing your shaft to snap.

correct me if i am wrong but mikes mounts replace one of the center diff supports making a direct rigid link between the spur and the pinion which should make the mesh much less likely to change.


Lastly resist the temptation to beat the crap out of your car with a sledgehammer take a break we all know how frustrating rc can be when trying to get a setup working well.

SpEEdyBL
08-12-2007, 07:51 PM
I guess I got what I paid for and I paid for what I got.

Mainly I was confessing why I wasn't able to complete my testing as promised other than the fact that the 8xl/mm and novak both are bad systems for 1/8 scale. I was almost about to ask mike to make a custom mount for the buggy, but I realize that everything is cheap on it, and I am now thinking about selling it and looking into a losi 8ight, which should have a better tranny and be easier to work on.

billmck
08-12-2007, 08:46 PM
the mbx has trash gears in its stock form, you could get the hardened gears from nitrohouse..those gears crumble with the old force21.


bill

ElectricThunder
08-12-2007, 10:58 PM
You need a hug Speedy. I'll let someone else give you one though...:D

Hey, on the plus side, MAYBE Novak is reading your post right now and saying to themself "Hmmmm....1/8 conversions are getting more popular, maybe we should take a looksie at what kinda motor power and design these require; perhaps a 5mm shaft on our HV motors would please some more people?".

I bet Novak is going to release a new HV system soon too (soon being a relative term- hopefully by the end of the year if not two or three months into next year. That's pure conjecture though).

CharlieS
08-13-2007, 02:07 PM
We're like 4 steps a head of you ET.......

ElectricThunder
08-13-2007, 02:13 PM
Novak FTW!

C'mon Charlie. Just hire me already. I've infiltrated your secret workings...:D (Maybe I should change my major from Aerospace to Electrical Engineering.....hmmm....)

ta_man
08-13-2007, 06:27 PM
We're like 4 steps a head of you ET.......

Which steps are those? Can I get a Endbell/Rotor combo for my HV6.5 with a 5MM shaft now?

CharlieS
08-13-2007, 07:39 PM
ET- We're hiring. :)

schenck77
08-13-2007, 07:55 PM
We're like 4 steps a head of you ET.......

good to hear. A little more info would be nice though, if you could. maybe a new esc to go along with a 5mm shaft motor?

ElectricThunder
08-13-2007, 10:01 PM
ET- We're hiring. :)


I'll be sure to call you in 4 years.:) (After all, Aerospace Engineers DO have to take electrical engineering courses along with a whole bunch of mechanical engineering courses...)

SS Pede
08-14-2007, 07:29 PM
Hey I want in on this too, I'm Mechanical Engineering! Hehe. :)

I think Novak is always 4 steps ahead of us. I can't believe how many quality new products they keep putting out. Though obviously SpeedyBL has not had the best luck with those rotors. :(

got2bqik
08-14-2007, 07:56 PM
I have had set-ups fight me like that.1 thing after another and none really related to the other. In the end it all worked out so hang in and keep wrencking.
Tim

ElectricThunder
08-14-2007, 08:43 PM
Though obviously SpeedyBL has not had the best luck with those rotors. :(

I think the shafts are hollowed out, so I wonder if that's the reason they keep snapping. I also wonder what kind of material the shaft is; if it's hardened steel, that's some crazy amount of force being applied to the tiny 1/8" shaft.

Have these shafts broken on a regular basis in the Emaxx and other monster trucks as often as teh 1/8 conversions have experienced? (just thinking aloud here I suppose)

got2bqik
08-14-2007, 09:01 PM
"What if" (the magic question) you filled the hole with jb weld, solder, or a screw.Shouldn't help but you can always try.
Tim

chilledoutuk
08-14-2007, 09:54 PM
sorry ET but I cant believe that a 1/8th inch shaft can be hollowed out and have any strength to them whilst still having a machined flat.

I think that as the use thicker shafts that are now machined to 1/8th inch diameter they use a center in the end of the shaft so the shaft is held still whilst being turned to the thinner diameter which i think might bee done after the sintering process as the high temperatures could cause such a small diameter to corrupt and become untrue.

RobK
08-14-2007, 09:59 PM
My HV 4.5 is holding up fine in my Revo so far. The Revo (based upon a 3.3) has the 2 speed stock tranny with a center diff & dual mech. brakes, RC Monster motor mount and 1/8 shaft mod1 pinion gear from the same, and 4S 8AH Maxamp lipos. I have run the packs down about 5-6 times since I finished this conversion, but the 4.5 keeps shreading tires & breaking the diffs. Part of my problem is I run on the street with high traction tires. I probably also need to back off on the slipper a bit, but I think its the braking that causes the most stress for some reason. I'm hoping some Fastlane diff cups will help and some thicker fluid in the center diff (going to 500K) will help the front tires; I'm waiting on the parts now. Truck weighs about 10.5 lbs RTR with batteries.

The ESC gets too hot after about 15+ minutes of running, but I think that's because I'm geared a little taller than I would like with the 2 speed. I changed the shift point a bit so I'm in 1st unless I'm doing a top speed run (or diffing out the front tires like mad).

Oh yea, I always use thread locker on metal to metal--lost too many pinions & other screws myself.

If I were Speedy I would get/make a stronger motor mount--could be the problem.

-Rob

ElectricThunder
08-14-2007, 10:09 PM
sorry ET but I cant believe that a 1/8th inch shaft can be hollowed out and have any strength to them whilst still having a machined flat.

I think that as the use thicker shafts that are now machined to 1/8th inch diameter they use a center in the end of the shaft so the shaft is held still whilst being turned to the thinner diameter which i think might bee done after the sintering process as the high temperatures could cause such a small diameter to corrupt and become untrue.

Maybe that's what I noticed; the little hole that is used to hold the shaft as it's being machined into a smaller size (I know the shaft piece that the rotor actually sits on is quite a bit thicker than the 1/8" part that the pinion goes on).

tcolesen
08-15-2007, 01:12 AM
ET- We're hiring. :)

You've got email :).

Hey ET, I just might be your west coast counterpart - I too will be completing an Aerospace Engineering degree, and hopefully I will double major in Mechanical Engineering, at the University of California, Irvine (yes, the same Irvine that Novak is located in :)).

ElectricThunder
08-15-2007, 01:40 AM
You've got email :).

Hey ET, I just might be your west coast counterpart - I too will be completing an Aerospace Engineering degree, and hopefully I will double major in Mechanical Engineering, at the University of California, Irvine (yes, the same Irvine that Novak is located in :)).

I know; I'm Five-Oh-Joe over at RC Monster's forums.;) Lucky you have Novak by you though. Oh well....I got NASA (Kennedy is about an hour or so away from UCF:D)...:p

SpEEdyBL
08-15-2007, 02:22 AM
You want to know what's funny? If you put the shaft of the second broken rotor next to where the first shaft broke on the first rotor, its almost a perfect fit! The mounting face of the motor was a good 15 mm away from the closest side of the spur gear and a fair amount of the pinion gear was hangin over the end of the shaft.

trf415
08-15-2007, 11:54 PM
I think thats the problem - too much space between the pinion gear and the motor. There is just too much stress being applied to the shaft. You should try using the long shafted pinions from Mega Motor USA. I think they would stop alot of the stress that is being applied to the shaft between the pinion gear and the front bearing.

SpEEdyBL
08-16-2007, 02:09 AM
I really am not going to run the novak in a buggy any longer. I'd rather have absolutely no chance of the shaft breaking. The fact that these buggies don't have slipper clutches is the real problem.

chilledoutuk
08-16-2007, 07:57 AM
well thinking about it the long shafted pinions wont make a difference as the problem is the leverage of the presure being at the tip of the shaft which is why it breaks at the point where the shaft suddenly gains thickness.

GSMnow
08-26-2007, 12:21 PM
I was just thinking about this one. I have not seen the car where you are having this problem, so this is speculation. Can you use spacers or shims to move the spur gear towards the motor can? Can the motor plate be moved to reduce the overhang? Could a long pinion be setup to have a support bearing on the far end past the spur?

Just some ideas to reduce the stress. Losi was very smart to p[ut the spur gear right up to the motor plate on their electric stuff.

SpEEdyBL
08-26-2007, 04:00 PM
My conversion had a motor plate mounted onto the rear diff bulk instead of the mount replacing the diff bulk completely, which caused the motor to mount further a way from the spur - 4mm further than it need to be, which was the thickness of the plate. Anyhow, I have my 8ight now and im just going to use mike's mount for it.