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Old 08-05-2010, 10:36 PM   #91
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Shaft flutter- I tested my TC4 on the bench with full throttle, a huge 38 tooth 48 pitch pinion at full throttle. Nothing but smooth. No drive shaft wobble. I realize as the car ages this becomes a problem and even is a problem with new cars on a high speed open mod layout.

So why does mine not wobble.
First it is a new Aluminum shaft which have proven to be the straightests. I tried associated composite shafts previously and was not happy. I returned to aluminum.
My shaft has stayed straight in the crashes due to the slipper spool in front.

My drive cups are new. This is imprortant. The shaft should be a snug fit in the cup as you install it. Replace worn cups that let the shaft go off center.

my pinions are properly shimmed for low end play. This keeps the input shafts running more true.

My bearings are relatively new and have low slop.

Anyway this is not a problem for me yet.

Race Report
I and the car continued to improve. I plumped up another battery with a long practice run. Time for some gear experiments.

I dropped four pinion teeth. The car lost some punch and top speed, but I was rewarded with faster laps. 10.5's in practice. .2 better than my best previous race lap. So why the improvement. I seemed to keep the corner speed higher on the very tight track when the car had less punch. I probably ran some 10.4's in the race. I am closer to the lead pack.

Anyway this alltime best way to adjust gears once your lap times stabilize within a few tenths for each of many laps..
Change the gear
Check the lap time for the top five or top 3 laps.
Go more in that direction if times improve. Check your motor heat though.
Current gear with the 13.5 is 66/34 x 2.5 = 4.85


I broke C-hubs in the first and second heat. I went home for lack of sufficient spares.
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Old 08-06-2010, 06:13 AM   #92
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Can't say I've burst a C-hub yet but I've been through a few sets of front hubs, damn cheap AE plastic just won't hold on to it's threads. Got some aluminum ones to test out now Pretty sure shaft flex is negligible on my car with a boosted 13.5t and the car was second hand when I bought it, it's had a new set of bearings all round but the main shaft drive cups were what it came with.
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Old 08-06-2010, 06:45 AM   #93
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This is why i like bouncing issues off of other people.

My drive cups are new... i even reamed the insides and lathed the outside of them (the Tc3 cup molding is horrendous, and the Tc4 cups are a little off) to ensure accuracy and balance.

My input shafts are new. Even the gear cases are new.

I have tried a mix of the Tc3 and the Tc4 cups and driveshafts... two were still NIP. All had the same wobble... and the Niftech titanium shaft for the Tc3 was the worst. I was starting to think it was harmonics.

The only paprameter i didnt consider was the bearings. I feel so stupid. lol The input shaft bearings run free and smooth, but they do have some years and many a lap on them. As a matter of fact, they are the original style Teflon sealed bearings. Ugh... thanks guys.
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Old 08-06-2010, 07:44 AM   #94
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Quote:
Originally Posted by John Stranahan View Post
Shaft flutter- I tested my TC4 on the bench with full throttle, a huge 38 tooth 48 pitch pinion at full throttle.
Could you tell me where you got that 38t Pinion? I run 17.5, and got to the point where I couldn't gear up anymore with 48p because I couldn't find anything above a 36t or 60t spur. So now I'm running 64p because theres a little more selection in gears. Oh and I'm running a 4.09 FDR I believe.
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Old 08-06-2010, 12:41 PM   #95
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I got my big pinions including this 47 tooth at Stormer, but I see they are out of stock at present on some of the big pinions.

https://www.ssl-stormerhobbies.com/c...=ns&pn=RRP1347

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Old 08-06-2010, 09:33 PM   #96
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I got to mess with setup on my Tc4 and another locals FTTc4 today at the track (as well as my Tc3).

Both Tc4's exhibited the same steering issues. Both were corrected similarly. I drove both cars thoughout the day after various changes to improve each. With that i have a question John...

Does your Tc4 tend to bring the rear end out on throttle coming OFF the corner? Diff or spool didnt seem to make a notable difference... neither did caster changes. Its on power oversteer.

Of course the tub car setup differs compared to the FT car. Roll center, shock position, etc. Spring choice was real close. Most of that comes down to the stiffness differences between the two cars (both in chassis and shock tower material differences). Both exhibited the SAME steering issue though. I even tried the shocks off of my Tc3 on the Tc4 and the issue was still present.

Im convinced its the Tc4 steering rack. Any thoughts?
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Old 08-06-2010, 10:54 PM   #97
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My car does not have the on power oversteer to a great degree. I dialed in just a little in to make sure I was steering as hard as possible.

What I find affects this the most is rear toe-in. Make sure to have at least 2.5 degrees.

Cars with a locked diff behave a little funny on power due to tremendoes amounts of front torque steer which is absent with a ball diff. With a locked diff try some reverse tuning to reduce the oversteer like going more inboard on the top of the front springs. This reduces load on the outside front, reduces torque steer, reduces oversteer.

With a ball diff go stiffer in the front (normal tuning) to reduce oversteer.

I don't think the rack (TC3) vs bellcranks (TC4) steer much different in my experience. I have run both. The bellcranks don't get sticky on center which is what I like about them.

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Old 08-07-2010, 06:53 AM   #98
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@DaveW

I run a FT TC4 in RCGT... can you post your setup in the rear? I haven't had that issue at all.

I've sometimes had oversteer entering a corner or on high speed turns. Spring or camber changes solved those problems.
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Old 08-12-2010, 10:49 PM   #99
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Track test 139F track temp, 104F pit temp. Then a race test in the evening cool. 91F air temp.

Rear Toe
During the mid week practice I noticed I had just a bit too much on power oversteer that we just discussed but only in one corner. time too tinker. I increased rear toe-in to 3 degrees by using stock associated rear hubs instead of Losi 1/2 degree hubs on the wrong side, with the 3 degree rear block. This is what I noticed. The oversteer was reduced to neggible, but corner speeds seem to be reduced also. The car did not roll as well. I thought I should get lap times before a final decision, but I felt the car was slower with more rear toe-in.
At the race I tested the 3.0 degrees of rear toe, I got a long string of very onsistent 11.5's but I was off the pace from last week. I went back to 2.5 degrees toe-in. The car was doing some 11.1 now with Sorex 32. I put on the sweep 30's and was about .1 faster and broke into the 10's a few times.

Tires
In the race I tried Sweep 30's, then a heat with Sorex 32, then a heat with Sorex 36. The sweep 30's still had the edge and I liked the way they gripped the best. You can have too much grip, and although the Sweep 36's were almost as fast they were about .1 slower than the Sweep 30's. The Sorex 32's were third.

I made no personal lap time improvements over last week but we had slightly less traction than last week when lap records were being set. I am still at about 10.5 for my fastests laps. A few tenths more needed.

Here is short video on the very small track during warmups today. Marcus is trailing in a 1/10 Sedan which is the class that I run, He is chasing a TTR or 1/12 touring car being driven by Sam at M&M Hobbies in Houston.

http://www.stranahan-rc.com/M_M_Hobbies_Practice.avi

John
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Old 09-05-2010, 08:52 AM   #100
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Any racing of late John?

I finally got back to the track with a rebuilt car. New bearings, layshafts and the whole 9 yards. Its probably the LAST time this thing will get that kind of work done to it.

Good news? The car was great at the track yesterday! Bad news? My driveshaft still does as pictured before.

Both my Tc4 and Tc3 have shaft flex. Both sound like they are gonna chuck the mainshaft when they hit the straight. Frustrating...
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Old 09-05-2010, 10:37 AM   #101
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Dave-Sorry to hear about your driveshaft wobble. I have to wonder if the driveshaft has a slight bend. If you have these take it out and rotate it over v-blocks with a dial indicator in the middle. I have done this for aluminum arrows. Then you apply some force with a curved object to the high spot until you get it straight.

I have done some racing since last report. I seem to do well in the daylight in prerace practice. Then the shop lights on 6 foot stands go up. Two of these are aimed right at the drivers. When it gets dark I don't do so well. I am stuck at about .5-1 seconds/lap behind.

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Old 09-06-2010, 03:32 AM   #102
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Sunglasses at night We race at night here to with just the lights from the parking lot poles. Bright colored paint jobs work best. Thanks for all of the info it helps alot AzRon
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Old 09-30-2010, 07:42 PM   #103
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My Tc3 tub suffered catastrophic damage... so i have been forced to ready the Tc4.




I finished the Tc3 rack conversion. I have a few more pix but this just gives an idea. If the weather clears i will get a chance to run this weekend and give some feedback.

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Old 10-25-2010, 10:02 PM   #104
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Hi,

Can I remove the bearing seals from the inside of gear cases and uprights?
I just want less drag overall. Will this have negative effects like causing more
wear on the bearings?

I also have some slight main shaft wobble. Is it necessary to replace it with
newer drive cups? Or putting new cushions on both ends will minimize the
wobble?

Thanks
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Old 10-26-2010, 08:17 AM   #105
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Quote:
Originally Posted by Airflow View Post
Hi,

Can I remove the bearing seals from the inside of gear cases and uprights?
I just want less drag overall. Will this have negative effects like causing more
wear on the bearings?

I also have some slight main shaft wobble. Is it necessary to replace it with
newer drive cups? Or putting new cushions on both ends will minimize the
wobble?

Thanks
If you have AE's black rubber sealed bearings in your kit, it might do you some good to take one seal off of each bearing, and make sure the open sides face each other in the gearcase or hub. There will be no extra wear from this. Its been done on Tc3/4's since they were first introduced.

The black seal bearings are OK, but when youre ready to step up to a better bearing, look up AVIDRC. Excellent bearings and they are $1 a piece.

Mainshaft wobble is common. All you can do is make sure the 4 bearings that support the layshafts are in good condition (dont know how old your kit is), and the same layshafts arent excessively worn (if you can clean up MOST of the marks from the bearings with 1000 grit wet sandpaper then youre good).

For mainshaft cushion, i use the little center piece of foam that comes out of the VCS shock foams. I then cut that in half with a razor blade, and put half in each cup. The shaft still needs to 'float' though. You dont want the cushions pushing against the ends of the shaft all the time. You may need to trim your foam accordingly.

If you want to take the time to ream out the inside of the mainshaft cups, and have access to a lathe, you can turn down the outside of the mainshaft cups removing some weight and excess material. This helps but, if you strap in enough motor, youre still gonna get some wobble.
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