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Old 08-27-2007, 11:50 AM   #136
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Ripples
I was getting a wear pattern over about 90 % of the tread. I would not try to move the scuffed section to the middle, but try to get wear accross most of the tire. The inside 10% shows no pattern so a tiny camber correction you suggest would be warranted. The scuffed section does show that the tire is slipping a little. There were few marbles there so it is a little too hard a tire. I was getting good lap times so I did not change to tires with a different heat rating . A little sliding sometimes keeps up good corner speed.
My RP40 I am running outside at 136 F show very tiny ripples accross the whole tread. They are wearing nice and even. You can feel these ripples with your thumb although they are hard to see in some lighting conditions.
John

I'll check into that loom cover. It is such a tiny order though. I should get a nice new clean one with each expensive motor.

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Old 08-27-2007, 04:05 PM   #137
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Here is a more recent pic of the wear pattern on the front of the TC5 using Takeoff RP40's at 136 F track temperature. The wear pattern in this case is pretty uniform and even accross the whole tread. Traction is super.

I did some tests on RC tires on granite. If you pull on the car sideways with a spring scale you can see a little more how tires develop their best grip. Normally objects have there best grip when they are stationary and loose some grip as soon as they start to slide. Rubber is different. You reach a high friction point when the car just starts to slide, but then you can increase the load on the tire some more as it slides sideways on the surface. In other words there has to be some drift action to be at the limit of cornering. With the full size cars I tested you can hear and feel when the tires start drifting and can keep the car at that point. With the RC cars you see this drifting after you get some experience. Think of the tire having a 1000 tiny fingers on the contact patch that are walking slowly accross the surface at high cornering g's. This sliding is what develps these ripples as at various times the little fingers of rubber are torn away with high cornering forces.
John
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Old 08-27-2007, 06:16 PM   #138
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John: when are you going to share your views on using front spool vs. front ball diff?
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Old 08-27-2007, 08:20 PM   #139
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yyhayim-I think I will wait to install one in the TC5 until steel parts are available. I like the sanpaper friction type of spool that you make from a regular diff. I helped pioneer this on the XXXS. You just remove the balls and replace them with a disk of friction material. Losi has a part number for the XXXS for these sandpaper disks which should fit our car.
I can give you a few bits of tech now though.


Standard ball diffs
A standard ball diff and a gear diff work similarly in that they always give almost equal torque to both drive axles. This has good and bad effects. It is good in that the car will tend to go straight on power. One side will pull just as hard as the other. It is bad in that loss of traction on one side will reduce the torque on the other. Both axles will still receive equal torque, but it can only be as high as the wheel with poor traction.

Torque Steer
If you take a two wheel drive truck with a ball diff and have an excess 1 ounce on the right rear you will find that the torque is almost even with the ball diff, but the heavier side tire will have just a little more forward traction and will pull harder than the left side. The truck will veer to the left,on throttle, if you remove your hand from the radio wheel and goose it. This is the reason to balance your car left to right. The right hand tire pulling harder applies a torque steer whose arm is the length of the drive axle in a counterclockwise direction when viewed from above. Notice the more loaded tire applies the most torque steer; it has the most forward traction from the extra weight.

Corner Exit with a Locked Diff
With a ball diff, on corner exit, the inside wheel is unloaded it will tend to spin. This reduces torque to the outside wheel. The car accelerates slower than is possible. If we put in the locked diff now, that outside wheel is locked to the driveline. An inside wheel losing traction will not reduce torque to the outside wheel. You can see, though that the torque is highly unbalanced now. The inside wheel is lightly loaded and applies little forward thrust. It is also overdriven (wheel spins faster than the road moves by) this reduces its forward traction even more. The right side front tire is heavily loaded, If I am turning left the outside tire provides a very strong torque steer to the left (counterclockwise when viewed from above). So you get a boost in forward traction as well as an addional steering tendency to the left; good and good. This effect is on power, you tend to apply some power going into the corner with a locked diff; moreso than usual. As far as I know this theory originated with me. I have not seen it elsewhere, but it explains all the facts to follow.

Setup with a locked diff
Traditional setup no longer works with a locked diff. Normally you get less cornering traction on an axle the more lateral weight transfer there is. Now you lock the diff and are cornering with forward traction of the outside tire (torque steer). The more load you put on this outside tire the more forward traction you have, the more torque steer you have, the more steering you have.

I did this experiment with the XXXS, TC3 and the JRXS in my usual number of steps. I increased the front spring tension a little (with a locked diff) and then increase it some more but by quite a bit more. 17lb to 19lb then to 25 lb then back to 17 lbs. By the time I finished going stiffer the car was doing tight donuts in the corner (huge oversteer). The car returned to normal at 17 lbs. This is telling me that things are backwards. The theory above explains why. Now this means that changes to roll center and swaybars will also tend to work backwards than normal with a locked diff. Christian Tabush and myself have verified this on several tracks. You are welcome to repeat these experiments.
You get very good corner exit speed, good cornering, and great braking with a locked diff. A little push on corner entry; just add power.

One-way
So then what about the one-way. A key difference between the oneway and the locked diff is that the inside wheel need not be overdriven with a one-way. In fact it is driving as hard as the weight on it allows. It is not locked to the outside wheel only to the driveline. There is less torque steer from the outside wheel because of this and more normal steering. I always setup the one-way equipped car the same as the ball diff equipped car. Almost all the benefits of a locked diff, but forget about any braking. The best corner entry traction of all the diffs as the front wheels cannot be braked to soak up some traction.

Wear from a Locked Diff
When you run a locked diff and jam a wheel up against the boards and brake it to a stop the entire driveline momentum tries to turn that one wheel. Usuallly, you snap an oudrive or axle. When you lock the front diff, vibrations from that supposed CVD are not dissipated to the other side by the ball diff. There is hugely rapid wear of an Aluminum bone at the CVD pin. I used to keep a half dozen TC3 Aluminum spare bones and redrilled those cups. I had a locked diff eat an aluminum spool up in two runs (with no pin pillows); pin pillows are a must for aluminum spools. A locked standard steel outdrive will hold up the best under locked diff abuse. LOSI LCD's greatly diminish these wear problems but not the breakage.

Pics from left. Losi JRXS locked up with sand paper disks. Losi JRXS standard ball diff. TC4 aluminum Spool showing wear from two runs. Right Losi JRXS oneway showing outdrive bearing on outdrive and oneway bearing inside diff tube. The O-ring seal was nice except very hard to install.

John
Attached Thumbnails
Associated Factory Team TC5, Brushless, LiPo, Li-ion Nanophosphate, Tips and Tricks-losi-front-ball-diff-locked-diff-011.jpg   Associated Factory Team TC5, Brushless, LiPo, Li-ion Nanophosphate, Tips and Tricks-losi-jrxs-ball-diff-guts-002.jpg   Associated Factory Team TC5, Brushless, LiPo, Li-ion Nanophosphate, Tips and Tricks-solid-spool-tc3-008.jpg   Associated Factory Team TC5, Brushless, LiPo, Li-ion Nanophosphate, Tips and Tricks-one-way-guts-009.jpg  

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Old 08-27-2007, 09:56 PM   #140
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I did this experiment with the XXXS, TC3 and the JRXS in my usual number of steps. I increased the front spring tension a little (with a locked diff) and then increase it some more but by quite a bit more. 17lb to 19lb then to 25 lb then back to 17 lbs. By the time I finished going stiffer the car was doing tight donuts in the corner (huge oversteer). The car returned to normal at 17 lbs. This is telling me that things are backwards. The theory above explains why. Now this means that changes to roll center and swaybars will also tend to work backwards than normal with a locked diff. Christian Tabush and myself have verified this on several tracks. You are welcome to repeat these experiments.
You get very good corner exit speed, good cornering, and great braking with a locked diff. A little push on corner entry; just add power.

John


john, just to clarify, so when using a locked diff, going stiffer on the front spring will give my car more steering? (on-power?)

BTW, did you also stiffen the rear spring? is there a difference in using a front locked diff and an alum spool?


thanks again.
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Old 08-27-2007, 10:13 PM   #141
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highwayman-Yes with a locked diff, I find that you put on a stiffer front spring you get more on-power steering. You also find that you will drive the car with more power through the corners than you would with a standard diff. A locked diff and spool give the same result as far as handling goes. The locked diff (with sandpaper) actually allows for a little slip in the crashes and may save the dogbone once in a while. Usually not.

The gas guys used locked front diffs sometimes but they don't go through corners on power, usually their clutch is disengaged for the entire corner so the effects there are somewhat different. If we are off power that long the car stops dead in its tracks.

Stiffening both rear springs with a locked front diff will have the opposite to normal effect. It will unload that outside front and reduce steering (torque steer). Normally it causes oversteer. I have tested this as well as changes to roll center. You will find the car is not as responsive to changes as it was before though. This may cause some confusion unless you make a big change.

I like the way the car handles with a locked diff. Very predictable. Great brakes if you need them. I hate the extra wear and damage from running the locked front diff. That's why I am waiting for steel parts.
John

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Old 08-27-2007, 10:41 PM   #142
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highwayman-Yes with a locked diff, I find that you put on a stiffer front spring you get more on-power steering. You also find that you will drive the car with more power through the corners than you would with a standard diff. A locked diff and spool give the same result as far as handling goes. The locked diff (with sandpaper) actually allows for a little slip in the crashes and may save the dogbone once in a while. Usually not.

Stiffening both rear springs with a locked front diff will have the opposite to normal effect. It will unload that outside front and reduce steering (torque steer). Normally it causes oversteer. I have tested this as well as changes to roll center. You will find the car is not as responsive to changes as it was before though. This may cause some confusion unless you make a big change.

John


what was the rear spring tension in your experiments?


with regards the roll center in relation to a front locked diff... a low roll in front (hinge pin height) will now produce more steering than a high roll on asphalt... in the same manner that a low roll center in the rear will produce more rear grip? is that correct?
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Old 08-27-2007, 11:02 PM   #143
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I did not do the 3 big jumps in spring tension at the rear. It would be easy enough to do. I used 17 and 19 lb springs at the back. Once I figured out what was going on in the front experiment, the rest of the ajustments followed suit and I only needed to make small adjustments once in a while.

Normally with a standard diff, you lower the front roll center, you decrease front roll stiffness, you get more steering. You get less lateral weight transfer at the front because it is softer now than the back. The back springs take a set first and take weight away from the front.

If you lower the rear roll center, you decrease rear roll stiffness, you get more rear cornering traction. (These chages are the same as if you used softer springs. softer springs reduce the roll stiffness)

Now you put on the locked diff and all this is exactly the reverse. The reason is you are no longer steering with side bite of the front axle tires but with forward bite on the outside front tire almost alone. Now I cannot see this stuff happening. This is the only explanation that explains the way that the adjustments work on the track knowing ahead of time how tires behave to increased and decreased load..
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Old 08-29-2007, 02:37 AM   #144
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Rezenclowd3-Thanks for the additional part number for the shims. I have not got the car setup completely yet. I'll give some more driving impressions after I do. Maybe this weekend.

Thanks for the support guys. Boomer thanks for the shock info. A little more support for: you can easily be too stiff on shocks if your road is not perfectly flat.

TCfree-Thanks for the pic. Neat installation job. How did your side to side balance come out with 5 cells. Probably about right. I see that you have replaced the wimpy associated rod ends. Good move. I like Losi rod ends the best. So are those FTTC4 aluminum bones. Nice. Is the front a oneway. What material is the front outdrive. Are you using pin pillows. It is hard to tell from the photo. Whose front belt are you running?

John
Hi john, sorry for not replying if been busy, i didnt balance the car 'but will do tomorrow' i went of a pic of craig d's car wich i did copy, but i think with it being 5 cell it will be almost spot on i will let u know the results in a day or 2, the weight of the car rtr was 1400 dead on the scales this is without a PT, Yeah also i replaced the rod ends with better 1's but im also gonna try the yokomo 1's, The aluminum bones are TIR and it's a spool up front made by TIR also, dont need the pin pillows as tir made their shafts fit perfect with the spool, The front belt is yokomo team bomber wich nicley frees up the car

Thanks.
ste e.
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Old 08-29-2007, 10:05 AM   #145
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I did not do the 3 big jumps in spring tension at the rear. It would be easy enough to do. I used 17 and 19 lb springs at the back. Once I figured out what was going on in the front experiment, the rest of the ajustments followed suit and I only needed to make small adjustments once in a while.


so, as you increased front spring tension, the rear spring tension remained constant?
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Old 08-29-2007, 11:34 AM   #146
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TCfree-Thanks for the info. Look forward to your balancing report with 5 cells. So those outdrives are they aluminum or steel. Tell us how they hold up after you run the car a bit.

highwayman-yes. I just changed the front springs. In further experiments I changed just the rear spring tension on the back and just the roll center on the front. These adjust backwards to normal with the locked diff, but again the car is not very sensitive to small changes with a locked diff.

Rear Toe In
Fortunately rear toe works the same with both a locked diff and Standard Diff. More rear toe gives more rear cornering traction. I noticed one of the team setups was using 3.5 degrees rear toe on the TC5. I think I will try this as I have had to go maybe a bit too stiff on my front springs. The benefit here is the outer tire is run at a higher slip angle when cornering and develops more grip. For stock this is probably too much rear toe as it tends to slow the car on the straights. It has been raining so maybe a test later in the week.
John

The schematic shows slip angle for a front tire, but it is similar for the rear. You need some slip angle or drift for the tire to develop the best cornering traction.
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Old 08-29-2007, 11:56 AM   #147
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TCfree-Thanks for the info. Look forward to your balancing report with 5 cells. So those outdrives are they aluminum or steel. Tell us how they hold up after you run the car a bit.
Hi the outdrives are plastic with alu sleeves over them. i ran this last weekend 5cell with a 4.5 and thay are still perfect and that was with a good few hard crashes

Thanks.

ste e.
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Old 08-29-2007, 12:05 PM   #148
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Here is a link to those TIR spools. Nice design. It has some flex to absorb vibration fron the CVD and impact from the crashes. I noticed their CVD bones come with two sets of holes in the cup. 3 sets could easily be incorporated. Those are the holes I used to drill. That flexible oudrive should prevent some of the wear to these holes. I'll try one of these spools. Are they accross the pond yet.
John

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Old 08-29-2007, 12:56 PM   #149
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Here is a link to those TIR spools. Nice design. It has some flex to absorb vibration fron the CVD and impact from the crashes. I noticed their CVD bones come with two sets of holes in the cup. 3 sets could easily be incorporated. Those are the holes I used to drill. That flexible oudrive should prevent some of the wear to these holes. I'll try one of these spools. Are they accross the pond yet.
John
Hi again, im not 2 shure if thay are over 2 u guys yet but a few guys on rctech have already orderd them/recived them direct from TIR in the uk

Contact- http://www.titaniumracing.com/contactus.asp
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Old 08-29-2007, 09:03 PM   #150
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Tcfree-Thanks.

Chassis Stiffness
For a full size car on asphalt there never seems to be enough grip nor chassis stiffness. Great pains are made to make stiff roll cages, stiff monocoque tubs. The suspension works better.

On our RC cars and full size cars racing on dirt sometimes a little flex in the chassis is desired. The car transitions better left to right. It goes through bumps better with a little flex. The flexible chassis adds a flexure component to the suspension where the tire can move up but no high friction joints needs to move.

I have made test on the chassis stiffness of several cars. The results are expressed in Newton-meter/degree or how much torque does it take to twist the chassis 1 degree. I have tuned hands as a result and can just twist on the beast and tell you that the TC5 has one of the stiffest chassis that I have owned. The reason is probably the very long Aluminum bulkheads that are then tied together with a nicely x braced upper top plate and those double screws at each end. This should be the ideal setup for carpet. For asphalt maybe a little more flex is desired. This can be purchased in the Form of ITF chassis and upper plates.

I chose to add some flex with two extra large holes in the left side of the chassis which added only a tiny bit of flex and then by reducing the top plate to almost a carbon fibre rod which I suggested might be enough. It is slightly less than 1/4 inch wide. So the stiffness now is in between a Losi XXXS and a Losi JRXS which was also very stiff out of the box. The Losi JRXS was about 10 times stiffer in torsion than the XXXS if I remember correctly.

my electronics are working well on the battery strap. The only thing I did not like was the antenna crossed over the drive belt and was a little short on slack for routine battery switching. I solved the problem by moving it to the battery strap. Some guys actually take this tiny antenna and wrap it between the mushroom heads on the heavy duty type of velcro and make a flat antenna the size of the tiny receiver's upper deck.

left pic is of the TC5 Top Deck Mod and Antenna Mod. Right photo shows measuring the torsional stiffness on the JRXS. You don't need to take this measurement, but you sometimes do adjust the stiffness.

John
Attached Thumbnails
Associated Factory Team TC5, Brushless, LiPo, Li-ion Nanophosphate, Tips and Tricks-top-deck-mod-003-resized.jpg   Associated Factory Team TC5, Brushless, LiPo, Li-ion Nanophosphate, Tips and Tricks-1-losi-jrxs-torsional-stiffness-test-022.jpg  

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