John Stranahan

iTrader: (27)

TC4 RTR, Tips and Tricks for Stock, Etc.

A new racing opportunity has opened up in Houston at M&M near Chimney Rock and Bellaire. The track is a very smallish outdoor sealed asphalt track. Lap times are 10-12 seconds. Traction is medium low. Racing is in the evening and the settling dew has prohibited the use of sugar water as it never dries at this time of year in the evening dew.

I have also been running a Losi XXXS, and wide pan cars, on a large 280 x 70 foot 1/8 scale outdoor track.

This thread is not meant to replace the TC3 or TC4 thread. It will be tech heavy and have less chat.
Some of my previous threads include:
TC3 Assembly Tips, Factory Team Kit, Factory Team TC3
Pantoura, 1/10 pan car, 2S LiPo, tips and tricks.CRC Pantoura 1/10 pan car
The Losi LCD Thread. Losi JRXS
Associated Factory Team TC5 Tips and tricks. Associated TC5

This thread is meant to get the most out of a recently acquired Associated TC4 RTR kit which is to be used for stock motor racing on asphalt. Any other TC3 or TC4 or TC5 topics are welcome as readers will have years of experience with these cars. Advice will be given as well as graciously accepted. I plan to see if the car is still competitive against a crop of expensive double plate, double belt TC's.


First some History to explain Why a TC4.
The TC3 has probably the best shaft drive train to date. It is exceptional on indoor asphalt in stock motor racing. My second touring car was a TC3 acquired during the heyday of NiMH cells. I immediately was at least .5 seconds faster than My Losi XXXS on indoor asphalt. Note that the Losi XXXS is exceptional for mod racing. The driveline was just that much more efficient on the TC3 in stock.

Chassis Tweak and Motor Sag
The TC3 had some glaring problems, though. The most serious was the tendency of motor heat to pull up the right rear corner of the chassis. As the motor softened the thick plastic directly under the motor clamp, the top layer would tend to shrink on cooling and it started puling up the rear. On the right rear shock you would notice 1/8 inch or more down adjustment needed on the shock collar. Additionally the motor front would sag down affecting gear alignment. A good track practice was explained to me by Barry Baker at the last big race at Performance in Houston. Remove the motor right after each heat of a race. Kind of a pain. My cure was detailed on the TC3 thread.
Motor Mount Gusset
Motor Mount Strap
These mods were easy to do by hand with the Dremel and solved the Tweak issue. I showed them to Barry Baker after the race and he showed interest. Not too long after, both are incorporated in an all new aluminum lower motor support in the new TC4 to solve the tweak issue and the motor sagging issue.

Delicate Arms and pivot Blocks
The TC3 was designed as light as possible for a racing edge. Mere mortal drivers needed a little more beef in the arms. The TC4 delivers.

Torque Steer
The TC3 also has some torque steer. This is easily compensated by the driver in stock motor racing. When using a 3.5 brushless (a 1 Horse Power motor) outside at Mikes it make the car almost undriveable for an old fart. You will need the TC5 for this case.

Side to side Balance
With NiMH the right side of the TC3 car was too light. Some drivers milled the center rib partially to move the pack to the right. Barry Baker had a partially milled center rib at our race at Performance in Houston. He won the mod race with it. The New TC4 has a narrower center rib. With a 5000 mA-H LiPo, I had perfect left and right balance doing nothing. In spite of this narrower rib the TC4 has a stiffer chassis than the TC3. I made some extra cutouts in My RTR to lighten it and make it more flexible. The narrow center rib also provides a lowered rotational inertia on the vertical axis for quicker response in the chicanes.


Sticky on Center Steering
This was caused by dirt buildup in the steering rack and was eliminated in the TC4, by using bellcrank type steering. You used to have to clean out the TC3 rack every session with the back of an X-acto knife.

I will detail some of the mods I made in future posts.

These mods include:
Chassis cutouts to lose .3 ounces, Aluminum screws to lose .5 ounces.
Slipper spool made from the Losi Slipper spool pads.
Gear lash adjustment and lubrication.
Lowered roll centers.
Motor Mount Clamp lightening.

Here are a couple of pics of the car ready for its second outing. The first outing already was about 1 second faster on the tiny track than my mod car the Losi XXXS with the addition of a 13.5 super stock motor.

How to get a TC4
1. Convert your TC3 for $85 or so, See this post for a complete parts list to convert a TC3 to TC4.

Buy an RTR TC4 at StormerHobbies.com for $229 and sell the included electronics.

Buy a used TC4

John Stranahan

iTrader: (27)

Slipper Spool
I have done a lot of testing of slipper spools on my Losi JRXS and Losi XXXS. They are just Superior to any other type of locked diff in strength. I made a very early version of a slipper spool on a Losi XXXS tips and tricks for stocks thread just after the cars release. This thread is no longer in the archives.

Here is what happens in a crash. Lets say we wedge the right hand front wheel under a 2 inch PVC pipe in a crash. That wheel immediately stops. The motor armature is still spinning though with tremendous inertia. The inertia is all sent to spinning the wedged (stopped) wheel. If you have a locked diff made from a solid spool you will tend to
snap the drive axle or pretzel the drive axle
break the pin pillow if it is there
break the out drive right at the slot.

the reason is there is no give. One-ways are not much better. A slipper spool will slip in a crash and let the drive line inertia pass to the left side front wheel as it slows to a stop. They act like a clutch otherwise and are firmly locked.

The trouble with making a slipper on the TC3 is you have the gear lash to reckon with. You must end up with a unit very close in width to a ball diff or you will not be able to shim the gear lash properly.

Enter the Losi A 3325 slipper spool and Associated lightened steel outdrives. I clipped the perimeter of the Losi pulley with a cutter and got close to the pads. I sanded the outer perimeter to just touch the outer part of the pad. Now I could remove it easily without cracking it. I got some cracking just trying to pry it out. There are little prongs on the inside of the pads to fill the ball slots. They snapped in perfectly to the TC4 gear. You remove the balls, but use the steel rings. I removed only one shim and lash was perfect. That means they are the perfect thickness. The TC5 ones on the TC3 thread that Dave used may also be a good thickness with the standard steel outdrives. You need to be able to drop the diff in and have just a little play on the gears when you rock the spur back and forth.

Now for a lube.

Use Aero Car gear lube or the identical lube by LGB trains which I tested here for gears. It is a light paraffin. It will melt with just a little heat or rubbing. Otherwise it is a dry waxy coating attracting little dirt. I lube the gears through that upper hole in the case with the Red Socket head cap screw sealing it. This hole is open on the kit. Thread it with a steel socket head cap screw and then seal it with a short aluminum screw or dirt will enter.
That silicone diff lube the RTR car is filled with is just too sticky. I could tell just by spinning the wheels by hand on the new kit. I opened both diffs, removed the sticky grease and added the very lightweight LGB gear lube. The aero car lube came with a tiny brush that would enter the screw hole. Lube the rear gears lightly once a session so that you do not contaminate the gear diff.

Gear lash
Remove only enough shims to get a slight play . Making a sloppy gear train will lose you power with extra vibration at speed and with poor gear contact occurring too near the points of the gears. This type of contact loses the proper rolling action that gear teeth should have.

Why add a locked diff? It is just a rocket out of the corners. Equal to a oneway. If it is a slipper spool you have reduced drive line breakage and maintenace over that obtained with a one -way. A one-way outside is just a mess quickly and then the bearings in it start to fail. I expect an improved lap time in next weeks race.

So how free could we make this driveline? We could back off the pinion and spin it up with a front wheel and have it coast for 10 seconds. Not possible with any other type of touring car. That is the edge for stock. Note I don't like the oil filled and steel sealed bearings which made this possible. Use rubber seals instead.

John

pics, Losi slipper spool after trimming, sanding, and removing slipper pads in good condition. Top of gear case showing an extra hole that can be used as a lube port.

mpboost

Great thread!

I am running a TC4 in RCGT. I bought it as an RTR and gutted the electronics immediately. I think I finally got the setup to where I like it for the track I run on. But the big drawback right now is the weight. Of course I am running the steel spool up front, and steel out drives on the rear which makes the car heavier but also more durable (snapped a couple plastic out drives). I am also running aluminum CVD bones, threaded aluminum shocks and the aluminum 2* rear toe block. I am sure all of this just adds to the cars weight since I am pretty sure the plastic parts are lighter.

One of my friends is also running a TC4 (RTR originally) in RCGT as well. He has been tossing around some ideas for lighter drivetrain parts and chassis lightening. The info you posted is giving me some ideas.

John Stranahan

iTrader: (27)

Thanks for the post

Speaking of Weight
I agree. The car is a pig. With my electronics the car weighed 53.8 ounces. I put on red aluminum screws seen in the photos and dropped .5 ounces. I made some reasonable chassis cutouts and lost .3 ounces. See the bottom of the chassis photo in the first post. I plan to do the motor mount clamp mod that is in a link in the first post. This is probably worth .3 ounces. My goal eventually is the IIC weight of 51.3 ounces. Lunsford probably still makes titanium tierods and upper shock mounts although this is probably worth only .1-.2 ounces.
I am at 52.5 ounces

I agree to use steel outdrives on a front slipper spool. Use aluminum bones up front. I have had good luck with plastic diff and bones in the rear once you put on the slipper spool. With a spool the front of the car drives it more. With a ball diff the rear of the car drives it more.

Motor Mount Clamp Mod Accomplished.
This was worth .3 ounces. The car is at 52.2 ounces.

Note the 66 tooth Robinson Racing Spur. This fit with two mounting screws. It allowed 35 tooth plus 48 pitch pinions. 35 installed. Gear is 66/35 x 2.5 = 4.71

pejota

iTrader: (12)

Looking forward to keeping up with this thread!

Can you get us some pics or dimensions of the track? I run a TC3/4 on a 80x32 concrete parking lot track. Kinda like indoor carpet, but outdoors.

It will be helpful to me to compare your settings and track size to mine.

John Stranahan

iTrader: (27)

Pejota-Here is a link to the Hobby Shop Web site page. The track is now square but is the same basic size. There is room for expansion.
Scroll to mid page to the 1/12 scale track.

http://www.mmhobby.com/racetrack.html

Roll Stiffness, Oversteer/Understeer Balance
The RTR TC4 came with two plastic ball diffs. This makes the tuning very straightforward. It had two sets of blue springs and high roll center blocks front and back. I was using Sweep exp 36 R tires. On the first lap on the track this is what I noticed on the asphalt. I had way too much steering. The car was doing donuts on each turn. It also would do a snap spin coming off the straight into a right hander.

Roll stiffness is how hard it is to roll the car. You get more roll stiffness with stiffer springs, adding a sway bar or adding a stiffer sway bar, or using high roll centers.

On a double ball diff car you can increase the roll stiffness of the front to kill some steering. More weight will transfer at the front now and reduce the efficiency of the front tires. In a similar manner you can reduce the roll stiffness at the back and increase the efficiency of the rear tires to make the back end stick. Now it is often said to only adjust the end with the problem, but I am here to tell you that the front is tied to the back, the problem of oversteer understeer balance is always really on both ends and relates to the delicate balance of front and rear tire efficiency. You feel free to solve the problem from either end. I had copper (heavier) front springs available so I put these on the front. The oversteer problem was mostly solved. I adjusted the top of the front shocks out (stiffer) and top of the rear shocks in (less stiff) to fine tune out a little more oversteer. The car was now drivable and I was about 1 second faster than the XXXS on my 5 fastest laps. I still did not cure the snap spin problem coming off the straight and had a few errors as a result. I qualified 4 out of 7 cars.


Overall Roll stiffness
You adjust the overall roll stiffness of the car based on how much traction you have.
For high traction asphalt you can use:
high roll centers (high roll stiffness)
Stiff springs ( not much stiffer than copper, though, on asphalt)
Heavy sway bars.

This is not what I had. I had low to medium traction. The car was dancing over the surface as it was too stiff. It was not planted. I changed to the low roll center pivot blocks that come as a replacement after the race. I also changed the rear pivot block from 3.0 degrees toe which I feel is too much for stock to the 2.5 degree Aluminum Block. You can save a little weight here by using the 3.0 degree plastic block and the Losi JRXS 1/2 degree rear hubs placed backwards (on the wrong side). (for two degrees use the 1 degree JRXS hubs on backwards.)


Use Low Roll centers on Carpet
I'll note that on carpet with high traction you tend to get traction roll. Traction roll is increased by high roll centers. The chassis tends to jack up in the corners with high roll centers causing a higher center of gravity and thus an increased chance to roll over. You make low roll centers by lowering the inner A-arm pivot with the low roll center pivot blocks.

For a more complete discussion on Roll stiffness and tire efficiency check my on-line tuning reference. You just pick a few topics to read at a time as they come up.

http://www.stranahan-rc.com/corneringatthelimit.html

Timbulb

iTrader: (2)

I've always heard the TC3 is far superior to the TC4. Why would I want a hybrid?

John Stranahan

iTrader: (27)

Hybrid of what?

the TC4 is an evolutionary step of the TC3


Things that were improved are:

• No more chassis melting and the resulting chassis tweak on the right rear corner. This is the result of the new Aluminum Motor support.
• No more motor sag creating poor gear mesh
• No more sticky on center steering rack requiring cleaning every session. This is the result of Bellcrank steering from another TC3
• Stronger A-arms and pivot blocks. I noticed one racer added these to his TC3 on the TC3 thread.
• Lower rotational inertia on the vertical axis from the narrower center rib.
• More easily fine adjusted roll center by the use of vertical inner camber link ballstuds.

The great parts of the TC3, that very low friction drive train, a molded tub chassis, are retained.
John

John Stranahan

iTrader: (27)

Durability improvements for Stock

• Use the lightened steel outdrives up front with a slipper spool. Plastic outdrives, plastic axles (used with a front one-way or spool) and a ball diff are fine in the rear.
• Use the Aluminum bones up front. These are thick enough not to bend and will not crack and fail like the plastic ones at the outer pivot pin when using a spool.
• I took the opportunity to install 4 degree Caster Blocks: use an extra thin shim between the wheel bearings added to the aluminum spacer. Now you can really snug the wheels on without developing an axial load on the bearings. (side to side). This reduces friction.
• I use a thin layer of blue Loctite paste on the upper camber link ball stud and the lower kingpin screw. What this does is locks the screw and flanged bushing into a solid piece. It no longer works around in the crashes and stays put. If the part is difficult to remove later heat it with your soldering iron about 20 seconds. The loctite will liquefy and the screw or ball stud will remove easily.

A couple of clearance checks. My steel outdrives were thicker than the plastic ones. I needed to take a little off the plastic that supports the inner camber link ball stud. Other wise they rubbed and were difficult to install in the case.

It seems the steering link was rubbing the drive shaft. I took a little off its diameter on the top, but will replace it with the small Associated ball cups and a thin tie rod.

FrostyDude

I would say that for national level competition it would be worth getting the car down to the minimum weight. However, if this is only for club racing, then worrying about the extra 2 ounces of weight seems like you're taking things a little too far.

The extra two ounces only result in being about 4% heavier than the minimum weight. At a national event where everybody else is probably at the minimum weight that would be significant. At a club event where everybody is probably over the minimum weight, it probably is not worth worrying about.

mpboost

I get your point, and I am by no means a national level driver......however the guys I have to drive against even on the "club" level have years of experience, expensive high end carbon chassis cars, and some of them probably could easily compete on the national level. I am positive they easily make the minimum weight, probably even have to add weight cars. Last time I weighed my TC4 it was well north of 1550g even with the tiny Tekin RS in it.

That being said I don't think there is anything wrong with building a well sorted and optimized car while simultaneously working on ones driving skills. Plus it's fun to experiment!

FrostyDude

Well if your competition is that serious, then you probably need to lighten your car as much as possible. I didn't realize the competition at your local track was so serious.

pejota

iTrader: (12)

Noticed on the pic of your front dogbones that your body posts are on the outside hole.

Don't know what body you're running, but for the HPI fans, if you take a long grub screw and thread it into the inside hole, you can thread the body posts into those and they will line up pretty close to perfect for the holes in HPI bodies.

I'll post a pic tomorrow.

John Stranahan

iTrader: (27)

Thanks for the posts.

My view on weight is that if you are 4% heavy then your car accelerates 4% slower than the other guy. The tires run at higher load so they corner slightly poorer due to less efficiency. The drive train has a little bit more friction. In any race class its best to ditch the extra weight if it is easily accomplished. My car is at 52.2 ounces now. 1450 grams is I am sure the weight Frosty Dude and I are shooting for or 51.3 ounces.

I removed the aluminum rear 2.5 degree rear pivot. I replaced it with the replacement plastic low roll center rear pivot which is 3.0 degrees. I took 1/2 degrees of toe out at the hubs with Losi 1/2 degree JRXS hubs on the wrong sides. This did a couple of things. It lost .1 ounce. That is as much as putting on titanium tie rods. Additionally it shortened my wheel base back to the kit length so it fit the body better. This should be better on my tiny track.

Drive Axle Angle
Also drive axles are now swept a tiny bit forward. There is a small down force added to the tire when you accelerate if the axles are forward. This helps give you more grip in stock.

Pejota-thanks. I will keep that in mind.

John Stranahan

iTrader: (27)

Track Test
traction medium-low
100 F air temp.
Low roll centers and changing front gold to the blue spring was an appreciated change. The car was more planted. I lowered the overall roll stiffness. Snap spins coming off the straight were eliminated. I could use some brakes there now to make the unbelievably tight turns that follow. You are at full lock.
Motor Temp was now in the 160F range after a long run. The gearing is close to right with the 13.5. 66/35 x 2.5=4.7. I have some punch now out of the corners. I have never had to use full steering throw to make the corners tight. It seems to help to tap the brakes beforehand to keep from overshooting the turn.
I put 30 weight oil in the shocks with little change.
One problem remains but only if I get sloppy and start using too little throttle. The rear end then drifts out like, for example, coming onto the straight. This may not be a problem racing as the runs will be much shorter and I will be more in a hurry.

Track Dimensions
54 x 72 feet, 246 foot run line. 16 mph average lap speed for a good lap.