John Stranahan

iTrader: (27)

smojoe-Yes just a few layer of masking tape bigger. Here are the specs on an individual cell

I have the assembled kit on the scales now. Pics in a bit with one LiPo on board.

John

John Stranahan

iTrader: (27)

I have decided to run the car light to give the speed control maximum chance at living in the Houston Heat. This requires some slightly different component places. I have tried this setup on the pan car and it worked well.

Front to back weight
It is often repeated that you want a 50-50 weight distribution for the best cornering. It is not often mentioned that it would be best if you had this 50-50 front to back loading on the tires while actually cornering rather than for the static case on the balance. To understand the difference you have to realize that on corner entry some weight will transfer forward from the deceleration of the car. Touring cars are low and long so the amount is small. I have also weighed some top drivers touring cars that have spent time adjusting weight fore and aft.
For the two reasons above and also because the car handles better and seems faster to me, I like to put about 2-3 ounces extra on the back of a touring car. With my current electronics and wishing to run the car light I plan to mount the speed control on top of the lowered battery strap. The receiver just aft of it. This gives me 2 ounces more on the back as shown in the first picture and also excellent side to side balance as shown in the second picture. Corner weights to come after I trim and solder things up.

Note that the chassis has two tiny holes centered on the shock tower. You can pick the car up with two points stuck in these two holes and lift the chassis. Both sides should lift at about the same time if you have good side to side weights.
John

The car is coming in at 46 ounces Ready to Race. 1 2s LiPo on board.

John

John Stranahan

iTrader: (27)

Electronic Fitment
I moved the tiny receiver forward so I could reach the factory antenna tube mount with the antenna. I think this setup will work great. I used MIP servo tape on the speed control. This tape holds better and does not release the speed control when it gets hot. Try some. I cut about 1/8 inch off each battery support post to lower the battery hold down bar down to the level of a Thunderpower or MaxAmp LiPo pack. I have about 3850 mA-h on board. The motor is in a very open space now. It may cool better. The car weighs 46 ounces with body and 1 LiPo.

Assembly Problems-The only problems I had were one dogbone had the pin insufficiently pressed in. It was off a lot. I tapped into place in the vise. The other was my caster blocks are on the wrong side. Must be that tiny type on the part. I am starting with blue springs low roll centers 35 weight oil, 4 degrees caster, No kickup or antisquat. Standard front diff. 6.5 mm ride height.

Outdrive Material
For mod the appropriate diff halves/outdrives, especially for the front, will be made from hardened steel. These were available for the old TC3/TC4. Hopefully they will become available soon for the TC5. Aluminum outdrives with pin pillows are OK, but are destroyed in a couple of runs if you loose a pin pillow. A pin pillow is a plastic cushion on the pins of the dogbone. I have a set of these for the TC5 but they did not seem to fit the standard outdrives.
If you run a locked front diff you will find faster destruction of drive axles and outdrives. This is caused by the vibration of the drive axle when the the single cardan type joint (not really a Constant velocity joint at all) in the drive axle is rotated. Best wait for stronger diff parts before you run a locked front diff. A standard diff dissipates this vibration by transferring motion to the other side when it needs to.

John

smojoe

iTrader: (2)

so the car is almost perfectly balanced from side to side with the electronics like that?

I need a lipo battery

John Stranahan

iTrader: (27)

Smojoe-It came out wihin about .8 ounces. That's pretty good. The motor side is still a little heavy. I could slide the speed control a little to the right next time I mount it. A heavier receiver or lap timing module could also be added. I will be adding a Spectrum Telemetry module to the battery strap later on. Things will be about perfectly balanced then. I ended up with only 1 ounce excess in the back. the telemetry module will bring this up a little. Note that the car is lighter than Roar Specs of 53 ounces. It is at 46 ounces. Should be really fast.
John

syndr0me

iTrader: (32)

How much of a concern is it to have the weight up high like that on the battery strap? My first reaction is to cringe, since we've been conditioned to believe that the lower the weight, the better, but I honestly don't know how important it really is.

rezenclowd3

iTrader: (17)

You should check out the Flightpower lipo packs. You can buy them in a 30C constant discharge rate vs most of the packs used (20C) Heli guys LOVE them, and they totally abuse their lipos.

DLS II

Actually they are a 5/4 C. My 2S2P pack is 5.75 x 2 x 1.125 inches. Those dimensions are slightly larger than a A123 pack because the cells are in an MEC SPT. Don (oops-I was at the end of page 1 instead of 2 sorry. This was answering smojoe.)

John Stranahan

iTrader: (27)

Syndrome-Well there are two choices on this weight if I want to run light. Up high with no torque steer from weight imbalance or down low with some torque steer and different steering left vs right from having too much weight on the left side; the heavier left side will pull harder if there is imperfect traction. Associated made a similar decision when they decided to put their center shaft and spur up high. Up high is not so bad as long as the parts up there are fairly lightweight. You can compensate a little bit by increasing the roll stiffness if neccesary.

I will also note you can raise the heavy diffs up if desired. I have them down low for now.

I think it's better to have the car accelerate in a perfect straight line when you are running mod. Especially if you don't have perfect traction. I will be outside on asphalt with lots of power on tap.

rezenclowd3-I'll check out those flightpower packs. Do you know who makes them?



John

John Stranahan

iTrader: (27)

Likes and Disklikes From a Visual Inspection


inner hinge pivots (pic below). I like these because they are mounted vertically. This gives them some flex in a crash. I experimented with this on my home built pancar front suspension. On the rear, of the TC5, I am running thick shims behind the hinge pivot supports in the back to give me 2 degrees of toe in. (Then I added 1/2 degree hubs to give me a desired 2.5 degrees.) If you point the shim in a direction other than straight down you will maximize the flex of these vertical supports and possibly reduce breakage in the crashes. I put similar spacers on the front (front and back of the pin) to bring the width out closer to 190 mm. They will provide my desired flex as well.

The diffs will pop out by removing 4 screws and taking off the shock tower and cap assembly. No need even to pop off the shocks and camber links. You can see two of the screws in the picture. This should make diff maintenance easy. You adjust belt tension by popping out the diffs and rotating two cams. The Losi JRXS pioneered this innovation and it is an easier adjustment to make on the Losi. You don't make an adjustment to belt tension very often, so I am satisfied with the Associated method and very happy there is no idler/tension pulley necessary.

Outdrives-I await the steel parts. These plastic outdrives are a little stronger looking than the lightweight plastic outdrives on the TC3, but not by a whole lot. They will tend to twist in the crashes, especially if you use a locked front diff.

Front CVD-The Losi JRXS pioneered a true constant velocity front Drive Axle, the Losi LCD. You really need a double Cardan Joint to have Constant Velocity. I wish the TC5 had borrowed this design element as well. It truly reduces the wear on the CVD joint itself, and on the outdrives, by eliminating most of the drive axle vibration when running a locked diff. For a standard diff the steel drive axle will work just fine. Maybe we will see some LCD aftermarket action here.

A-arms-The A-arms are much beefier than the TC3. Unfortunately what this does is cause breakage of the caster block in the crashes. Maybe an Aluminum Aftermarket caster block would be warranted. I have to run the car first to see.

Chassis-The car is lightweight and also very stiff in Torsion. I noticed the recommendation for an ITF chassis. These are in stock at Stormer. It would not be too difficult, though, to put some more lightening holes on the left side of the chassis to add some more flex for outdoor asphalt. I like the fact that the top strap which is responsible for a lot of tweak issues has double screws long ways on each attachment tab. This should prevent movement. I am glad they got rid of the stiffening rib (FTTC4) which always looked to me like a tweak nightmare. When you twist the chassis it should act like a taught spring. There should be no parts sliding on each other with twist. No creaking and shifting allowed.


more to come.

John

yyhayyim

iTrader: (26)

A few new Lipo packs to consider and test:

1) Flightpower EVO packs(I belive these are the ones suggested a few posts before) http://www2.towerhobbies.com/cgi-bin...?&I=LXRVT8&P=7

2) Trackpower: http://www2.towerhobbies.com/cgi-bin...&I=LXRWF7&P=ML

yyhayyim

iTrader: (26)

John...your left side with the LRP motor and esc and servo, should easily balance out with the right weight lipo on the right.

LRP 3.5 motor- 168g
ESC- 25g
Servo-60g
receiver- Spektrum Micro 7g, regular SR3000- 17g
--------------------------------------------------------------------
= +-277g (w/ Micro Spektrum), +- 287g with regular SR3000 Spektrum

Assuming you have the micro receiver, all that can fit on the left side, and there is good space for it all to fit on the TC5 wider chassis, a 250-260g Lipo will do the trick...Maxamps 5000HV is 225g, and you can add 6-7 7g ballast weights to get it perfect.

Or, use the Futaba low profile digital servo...45g, and that will drop your weight even more on that left side.

However, keep in mind that those running 5 and 6 cell nimh packs, the right side is much heavier than the left side...440g on the right side if running 6 cell 4200 size cells, and about 370g with 5 cells...and their cars are very well balanced...the physics on this evades me and would love hear an explanation as to why it is so...

ljohnson

The batteries are be closer to center than the electronics on some chassis. You have to look at how far from the center line the parts are mounted not just which side. Offset front belts and a motor sticking way out to the left both factor in here.

yyhayyim

iTrader: (26)

Also- you might want to have a conservative FDR to start with and then see at poin its too much...start in 10.75FDR range...

87S/16pX2.0 =10.8FDR

If you can get 6 min out of it w/o thermal issues, then go for 87/17 combo (10.2FDR, which might be too much in that heat)...

John Stranahan

iTrader: (27)

YYhayyim
lJohnson has explained things well. You cannot just add the weights up. It depends how far they are from the center line. When I do corner weights you will see that good balance requires you to put the weight in a good position fore and aft as well so one side mimics the other.
If in doubt, the scales are quite right. Also don't forget those two little holes in the shock towers. If it picks up off the table level then side to side weights are good. This LiPo pack is exceptionally light in the 6-7 ounce range. It is as far right as the chassis will allow. The electronics are nearer the center of the car. I'll look at your numbers later. I am running the car LIGHT (46 ounces) as I have no Roar Class to race in. Gearing is at 10.28 right now. I can go lower but the track is long. Thanks for gearing advice. Hauling that extra 7 ounces is partially responsible for frying our speed controls.

Roll Center
The roll center is the point about which the car rolls when it goes around a turn. Imagine yourself viewing the very front of the car. Someone standing to your left pushes sideways high on the side of the car. The car will roll to your right around an imaginary point that remains still. That point that remains still is the roll center. Now let’s make adjustments to the car. If the roll center is low, say at the ground, the guy pushing will have maximum leverage. The car will roll more easily. If the roll center is very high say at the same level that the guy is pushing, he will not be able to roll the car at all. He will have no leverage. If the car is small enough and he pushes hard enough the car will slide straight sideways without any roll at all with this high roll center.
For the real cornering case, the man pushing would be the centrifugal force in a corner. It acts on the center of mass of the car. For a TC5 this is about .79 inches above the ground. The roll center is a property of the suspension geometry that we can adjust fairly easily.
There is a bad side to having a very high roll center. Although centrifugal force acts always on the center of mass, the tires traction force acts directly on the roll center. The tread patch creating traction acts directly on a line from the tread patch to the roll center. If the roll center is very high this force aims up a little. This creates suspension jacking. The chassis is actually lifted up higher from cornering traction. This is bad. It is bad enough that touring car racers on carpet tend to use low roll centers to keep from traction rolling the car. The sequence that starts a traction roll with a high roll center is chassis lift followed by increased roll, followed by traction roll.

On asphalt outdoors you generally use a low roll center if traction is low and a higher roll center if traction is high. .25 inch high is probably high enough.

So where is the roll center on the TC5. I made a series of pictures. At the left the roll center is very low -.4 inch. This is probably unusable. At the middle it is at ground level or 0, On the right it is about .1 inch high. There are some advantages to having a roll center at the ground. The tires traction force is 100% in the correct direction making the car turn. In some cases touring cars will make too much traction, though. I think this is not possible for fullsize cars. For this reason we sometimes raise the roll center up to kill some traction on one end of the car that has too much traction.

I got my roll center numbers from a spreadsheet that I wrote to calculate roll centers. It gives numeric output as well as graphical output. It is written in Microsoft Excel which you would need to use it. A free download is available here. This particular sheet has my TC5 numbers for a roll center at ground level and 6.5 mm ride height. I am using the top holes in the Aluminum bulkheads. The long suspension support *. The camber link position you can see on the photographs.

left: long suspension mounts in lower hole RC=-.40
middle: long suspension mounts in upper hole RC = .01
Right: medium suspension mounts in upper hole RC = .1

You can fine tune with shims under the camber link outer ball stud. Adding shims here will raise the roll center. Lowering the inner A-arm lowers the roll center.

John