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Old 07-16-2010, 09:40 PM   #76
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Chassis Flex, Rear Toe in

By chance, I had an opportuninty to test my new mod Associated TC5R equipped with a 3.5 motor and 2S LiPo on this tiny track. Normally I run it on a 275 x 75 foot 1/8 th scale track. My TC4 was at home was the reason to run it; the big track was closed to practice for the World Championships. By the end of the session I felt the TC5 setup was spanking my TC4 setup, so I examined the two cars carefully at home. The TC5R with some mods that I had made to the top plate had more chassis flex than the TC4. It seemed to have more grip so I added some flex by cutting a side out of the triangular chassis braces. These braces are inexpensive so you can buy a second set if you want to go back. See the pic.

I had sway bars on the TC5 with slightly softer springs than on the TC4. I went to green springs and Chrome Sway bars on the TC4. I felt the better performance in the chicane was probably cuased by the increased roll stiffness.

The rear end of the TC5 was more planted off power than the TC4. I carefully measured rear toe by several methods and discovered the TC4 did not have the expected 2.5 degrees of toe based on the pieces I selected. The problem turned out to be that the inboard hingepin brace that goes accross the car is not the same front and back. One is marked with a circle, one is marked with a meaningless square. Well the square goes on the back suspension. I had the square in the front. After swapping these, then I got the proper toe. I had the 3 degree rear block installed with LOSI JRXS 1/2 degree rear hubs on the wrong side. This subtracts 1/2 degree rear toe. Anyway after correcting this error I had the 2.5 degree rear toe per side.

Rear toe in is one of the reliable ways to adjust oversteer/understeer balance once you lock the front diff. More rear toe tightens the car up (reduces oversteer) to a point which might be around 2.75 -3.0 degrees per side. Further improvements using over 3.0 degrees of rear toe with rubber tires on a TC may not be possible. Using less rear toe frees the car up in the corners and reduces friction on the straights.

I raced the car again last night after 3 weeks of rainouts. It felt much better. Lap times improved another little bit. Best lap was a 10.9 This is an improvement from 12.4 the first time I ran the little track. I need to improve another .7-8 seconds to be in the hunt for a podium place. A little practice may do the trick. I suspect the top guys have 1,000 more laps on the track than I do.
John
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Old 07-17-2010, 06:19 PM   #77
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Very interesting about those chassis braces...

I took them completely off my TC3 and found an amazing amount of grip with the HPI D-Compound Vintage Trans Am tires.
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Old 07-20-2010, 11:07 AM   #78
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Default TC4 Mod race setup

What is a good gearing for 5800kv motor for a TC4 for asphalt mod race with long starights?

My tranny gears are noisy always get stripped what is the beat fix for this?
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Old 07-20-2010, 01:46 PM   #79
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Gears
First contact. The gears should contact each other near the middle of the tooth, contact near the tips will make the gears weak. If you remove all shims you will have contact near the teeth. Reshim the gears so there is just a lilttle play back and forth when you rock the ring gear with your finger. If you break gears with a spool, check the first page and install a slipper spool. I am also told the Nylon colored gears from the NTC3 may be stronger for use with mod motors.

Lube-you need some kind of lube on the gears. Associated uses their diff grease in large quantity on the TC4 RTR gears. One advantage here is that migration into the ball diff will cause no harm. I like AeroCar Gear Lube. Links in a previous post. It is a very light parafin that liquifies on movement or heat. I add it through the extra screw holes in the case every session or two with a tiny toothpick like brush.

Ratio for a 7.5-Thats about a Novak 7.5 turn, gear it 7.0 in the touring car according to Novaks gear chart to start. Check temp early at 3-4 minutes, if you are hot, say over 160 or so, gear lower, check temp at 6 minutes, 180-190 F is OK. If hottter gear lower.
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Last edited by John Stranahan; 07-29-2010 at 11:26 PM.
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Old 07-23-2010, 04:08 AM   #80
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Wow great thread here,I was looking for info on TC4, can any one suggest a pinion and spur combo for 17.5 brush-less? thanks ''don't junk them-keep em rolling''
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Old 07-23-2010, 12:07 PM   #81
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Start around 3.5 from Novaks chart.

Track Report
I had a good practice with the car. The humidity was up so the track was not treated. My car was faster than the fellow that finished first last race. It was in the daylight though. I lose a lot at the night races from insuficient lighting. Cool weather let the Sweep EXP 30's run well. There was another touring car running faster, but he was using a 12t brushed so we were not exactly equaly powered. I made only a slight change to setup. I put a stiffer silver spring , all the way in, on the front to give a slight on power oversteer with the locked diff. Note this is reverse tuning due to the locked diff.
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Last edited by John Stranahan; 07-29-2010 at 11:25 PM.
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Old 07-29-2010, 10:25 PM   #82
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Race Report
I made some progress on lap times. The fastest were 10.7s with quite a few in a row. I qualified and finished 4th of 8. Still have .5 seconds to go, but the .3 second improvement was nice. We did not treat the track tonight so it is especially good news. Part of the improvement was using Sweep EXP 30's with Paragon Ground Effects (the smelly stuff) traction compound as we are outside. I had medium traction as a result.

One other little experiment. I took off the narrow Losi Hexes and installed medium Losi hexes for heat two. The car seemed faster. There was no improvement on the tiny track from narrowing up the car just a little. I am making progress rolling through the corners a little faster than before. This is my main gain. The setup which I updated is just outstanding.
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Last edited by John Stranahan; 07-29-2010 at 11:24 PM.
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Old 07-30-2010, 08:39 AM   #83
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John

Are you still running the slipper spool up front?

Have you thought about testing a ball diff?

On our track (80x36) we had a lot of 180*s and tight 90* turns. I always felt that the ball diff helped me get through the corners quicker, especially if my corner entry was off. Guys who ran a spool up front had one chance to get the entry correct and if they were off, they would accelerate into the boards.
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Old 07-30-2010, 11:08 AM   #84
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I ran the ball diff in the first race. There was an improvement going to the slipper spool. I am still using it. The car drives really well.

Note also I took four hits to the pipes that would have broken tc3 arms. No breakage in the last two sessions.
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Old 08-03-2010, 09:01 PM   #85
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Practice Session
My pit table under ccover was 107 F. The track was 137 F. I got in a couple of long runs. I changed to Sorex 36 tires due to high temps. I actually puffed up the battery by running it too long. It was not so much the power drain from running a 13.5, but the fact that the battery started at 107F and then was heated by 137 F track air and by power drain. Anyway I kept my second run to 8 minutes to avoid this. The car ran well with low-medium traction.
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Old 08-03-2010, 10:13 PM   #86
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nice
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Old 08-04-2010, 08:05 AM   #87
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John, any shaft flex at WOT for you? I have the flex in my Tc3, and the unboosted 13.5 in my Tc4 has it too. The Tc4 shaft hits the battery it flexes so much.

Quote:
Originally Posted by pejota View Post
Any pics of this setup? I think i understand it, but according to my teacher education classes, some of us are visual learners.
Quote:
Originally Posted by DaveW View Post
Im a visual kinda guy too... my digicam hates me.

The car is all set for a race in Jersey this weekend. When i come back i will tear the shocks down and lay them out for some pix.
I havent forgotten about you. I didnt make the race in Jersey for personal reasons, but decided to make the testing fair and built a Tc4... since my car is technically a Tc3. The Tc4 hit the track this past week for two packs dodging raindrops, so ill give feed back on the internal springs and if they work on this chassis once i can get some heat in the tires.

I dont wanna have to pull the Delrin stoppers out until i have to. They are pretty much a one use item and get changed each time. I have a set of the VCS upgrade stoppers being modified for this very reason (less work to source/make the stopper). Hopefully they hold up as well as Delrin.
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Old 08-04-2010, 12:04 PM   #88
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I don't get any noticeable shaft flex. We don't go very fast though. I did have some early contact with the servo link. I replaced the factory link with a steel link and rod end that is more compact. I had contact at the rear on the battery. cutting the ribs in the chassis out near the frame edge, moved the battery outboard and cured this.
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Old 08-04-2010, 07:29 PM   #89
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John, I've heard what Dave is talking about with the shaft flex, since there is a guy with a TC3 that went to a FT TC4. When the car is getting up there in speed, & at full throttle, it seems the shaft has a lot of flex for whatever reason. Maybe if you tried some high speed runs with a stock shaft, you will hear what they are talking about. Just a thought.

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Old 08-04-2010, 07:51 PM   #90
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This was before the 17.5 was on a boosted ESC. Im not even at full throttle, just pegging it and letting it spool up some...

http://s206.photobucket.com/albums/b...=ShaftFlex.mp4

... sorry bout the background music.
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