John Stranahan

iTrader: (27)

Mark

A spool has a lot of torque steer from the outside front tire. You load this outside front tire more by making the front stiffer. This increases the torque steer. Try less rear toe first but then try to make the front a little stiffer to add more steering traction. After this you could try the more flexible front arms.
John

Here is a more detailed post on this topic earlier in this thread.
Setting up your Roll Stiffness with a locked diff

bukil

iTrader: (39)

Update:
I raced this weekend. I TQ'ed stock novice class and won .I know I can still cut my lap time by a few tenths of a second or maybe even a second if I run consistent. I just need to work more on my setup and my DRIVING .

The changes that I made were 30 wt oil and -2.5 toe on the rear just like what you suggested John. It was better this time but I could still use a bit more on on-power steering. My wide turn (on-power) was noticably reduced but I still get it. Maybe I should slow down on corners a bit huh ?

I will try Gold springs (front) next time . I'm open to any advice.

Once again, I really appreciate your input John . Thank you.

Mark

John Stranahan

iTrader: (27)

Mark-One more thing you could try before you change springs. I had a problem opposite to yours while running a locked diff. I would loose the back end on power. I changed from front toe out to front toe in about 1/16". Check your front toe and maybe try a neutral toe or slight toe out.

Also if you think you are getting close to a neutral oversteer/understeer condition try just moving one hole out on the front spring or one hole in on the rear spring.

Thanks for the report and congratulations on your good finish.
John

bukil

iTrader: (39)

I have already tried messing around with the front toe. My setup seems to like no toe in the front. If I add toe out in the front, I oversteer when exiting the corners. But I will try moving the rear shocks inward more as it is on second hole from the right (shock tower). I will let you know what happens.

Once again, thank you John.

Mark

John Stranahan

iTrader: (27)

Track Temp132 F. Air temp 91. Nice blue groove left over from the weekend activities so I had good traction. Takeoff RP 36 dry

Flat Wire vs Round Wire Part II

If you have followed the thread you know that I tested a stock Trinity Flat Wire 10x1 (approximately an 18 gauge wire on a light D1 blank) and a Round wire 10x1 (a 16 gauge wire on a heavy D4 blank) previously.

Trinity graciously contributed a set of flat and round wire 10x1 arms on the same blank so that I could test the difference in just the wire if there was any. Here are the results of that test.

Previously I made a short run on the test arms to determine optimum gearing at Gulf Coast RC Race Track. They both like to be geared at 7.32 same as the 11x1. My race 10 x 1 likes to be geared just slightly lower at 7.47.

Today I ran four Trinity Cobalt motors in sequence. A round wire 11 x 1, a round wire 10 x 1 (15 gauge race motor) and then the two test motors both 17 gauge, both on D4 blanks, the flat wire third and then the round wire test motor fourth. All the motors were setup with octagon high silver brushes. I set the spring tension on the test motors at 4 on the trinity spring tension gauge. On the 15 gauge race motor I set the springs with a little more tension. 4.25 on the gauge as the comm wears too fast other wise.

The 10 x 1 round wire test motor ran very similar to the 11 x 1. It was very punchy out of the corners. I used some brakes coming off the straight and required about 7% more brakes on the radio to give me the same braking as the race motor. This might be just the result of the gearing change.

The 10 x 1 flat wire motor gave the best acceleration in the middle of the short straights, not too punchy coming off the corners. This suited the traction at hand and reduced the tendency to wheel hop coming off the tight hairpins a little. This motor was more powerful than the 10 x1 round wire of the same gauge. I got better top speed on the straight and better mid track acceleration. Braking was the same as the round wire test motor. Sound was the same.

This is opposite of my previous test on the stock arms which are highly affected by the blank that was used.

There are probably practical reasons why this flat wire motor is not available in bigger gauges on the heavier D4 arm such as the wire will not fit. I think I would like flat wire a lot with bigger wire on a heavy arm.. I liked the flat wire motor best of the two test motors. Possibly some square wire would solve this little problem of not being able to use the bigger gauges.

Neither test motor nor the stock Flat wire arm that comes with a lighter D1 blank is as lively as the big round wire 10 x 1. Running this delightfull race motor verified that my batteries were still in racing shape. I used two very similar packs that were each run once previously today to run the test.

Induction

Induction is the motor parameter that I am interested in, in these tests.

Induction is the amount of magnetism produced by each increment of current in a coil of wire.



The following factors give a motor more induction

A heavier arm

more turns of wire.

Wire packed tighter to the arm poles (flat wire, square wire or Hex wind, then quint then quad then tripple, and so on). A single has a lot of space when packed on the arm so it is packed on loosely.

---
A stock motor has many turns of wire and has high induction, poor top RPM, excellent part throttle control in corners. Good punch. Poor power at high amps.

A nine single has few turns of wire and has low induction, Great RPM, poor part throttle control (it takes a lot of trigger movement for anything to happen). Good power at high amps.

John Stranahan

iTrader: (27)

Latest GTB 6.5 Repair

I had previously noted in a post that when I received my remanufactured GTB 6.5 that the rotor felt weak. Well this time they only replaced the rotor. I had not mentioned the weak rotor to Novak only that it would go to full throttle at random times. It seems to work fine on the driveway now.

I have a picture of the sock I plan to use for liquid cooling the motor with rubbing alcohol. One capfull on the sock before a run should do it. The trim ring is removed. There are three layers of sock in this area. One layer is all that will fit on the JRXS elswhere. I'll report the results in a few days. No problem finding a hot day for a test now in Houston.

Losi JRXS Spool Pad

I had noted previously the problems with the Losi Locked Diff setup that compresses the pulley with sandpaper. The pulley eventually compresses and changes the pulley alignment to make it rub the shock tower and makes the diff slip. There is a relatively new part LOS A3325 That is a (harder) plastic center section for the pulley to hopefully eliminate this problem. They are in stock at Horizon. I have one on order.

bukil

iTrader: (39)

Update:
I moved my rear shocks one hole inward. I get oversteer on on-power steering . I moved it back to where it was. It was better. I might try putting a swaybar (AE thinnest - black) in the front next time I race and see what happens.

How do you guys install the swaybar (black) in the front without the cvd getting scrapped?

I did not TQ but I did finish second on the A-main.

Mark

John Stranahan

iTrader: (27)

Mark

When you get within one hole on springs then its time to tinker with roll center a bit. Try a thin shim under all the front pivots to raise the front roll center just a little bit. This will give you a small increase in steering with a locked diff. Smaller than a one hole movement on the shock tower.

I looked at a photo of an FTTC4 with gold sway bar. It looks like the sway bar links may be sligtly adjustable in length. Make them a little longer.

John

bukil

iTrader: (39)

Edit:
I finish second in the A main in sportman class. I was racing novice before. This is to prove that your advice (John) works. Thanks.

John Stranahan

iTrader: (27)

Mark-Thanks for the report. Note that I revised my previous post.

I ran one LiPo pack in front of the house to test the motor cooling sock. (picture above). 91F air Temp. Motor temp after the run was only 125 degrees on the bottom 105 F on top. Not too much sun, though, so I need some more tests at the track. I used a cap and a half of rubbing alcohol to wet my motor sock. It was dry to the touch after I finished my run so the alcohol is really doing its job by evaporating. The black exposed back of the motor was only 117 F. No fires, no trouble. It is showing promise. I geared over the suggested at 7.55. Very good performance and top speed.


You can easily go 100 yards down the street in either direction with the Spektrum.


Anyway if you decide to try this because your GTB motor is thermaling, give me a report. It's not as hairbrained as it looks. My sock did not rub the ground, but I am using a 6.5mm ride height due to some bumps or waviness on the track. I stapled a strip of sock together, but a baby sock might work better.

I have the improved Losi spool installed. Sure is nice.
John

J Tronzano

John,

Iwould like to try your set-up on asphalt, but need some clarification ona couple of issues.

Will it work with a Tight Brown Grease Diff instead of Spool, and if so would handling adjustments be the reverse of those applied to a spool set-up?

How do you determine the Roll Center Difference when changing Ride Height?

Thanks

John Stranahan

iTrader: (27)

J-The setup for a front Ball diff will be similar in that the roll stiffness is about right on my car for aphalt at a 6.5 mm ride height. When I swap between the two, locked diff to ball diff, I usually only change the springs a few holes.

With a front ball diff adjustments are more normal. Go stiffer in the front to reduce steering traction (move top of front shock out).

Fine tune with roll centers once you have the springs where you like them. Go to a higher roll center in the front to reduce steering traction (Lower A-arm pivots up). You get the idea.

I find that when you lower the car's ride height the car acts stiffer overall and slides more (there is less roll). To compensate use a lower roll center or slightly weaker springs. you determine how much by trial and error. Use shims, about .020 inch, under the inner A-arm pivots to make a move. Front and back to change the whole car. Front or back to fine tune the oversteer understeer balance.

John
Lots of rain lately has reduced my practice sessions a little.

J Tronzano

John,

Thanks for quick response, I'm just a little confused on one issue, in your last paragraph you state that " when you lower the car's ride height, the car acts stiffer overall (less roll). To compensate you suggest lowering roll center &/or weaker springs, very clear. However, in an earlier post "New Ride Height and Roll Center Adjustment" you mention lowering ride height to 5 mm from 6.5, which put roll center well below the ground so you raised the roll center by 040. Here's my confusion, do we raise or lower roll center when we lower ride height?

I don't mean to be picky, but I just want to do it right. As I'm going frm a complete high roll center set-up to your low to med roll center set-up and want to get it right.

Thanks for your help.

John T

Mike Haynes

iTrader: (2)

Johnny T.

You going to jackson tomarow, if so cya there, and i may grab your setup if mine don't work

I think im going back to diff

John Stranahan

iTrader: (27)

John-Several factors contribute to roll. The one that seems to be the major contributor when you lower the car is that the center of gravity goes down (.060 inch in your example). The roll center goes down too (.040 inch), but the net effect is that the car feels stiffer to me and has less cornering grip, if you had it adjusted well at the high ride height. This does not mean to run high. It just means you need to readjust things to run low which is preferable if the track is very smooth. If the track is wavy or has bumps you need to run higher to keep from puninshing the frame too much.

When the center of gravity goes down the lever (or moment arm) that the centrifugal force acts on is reduced. This arm extends from the center of gravity, where the centrifugal force acts, down to the roll center, where the supsension forces act. I do like my roll center near the ground as this is a more efficient place for it to be. More of the tires traction force is turned into cornering force when this is the case. Roll center within 1/8 or 1/4 inch of the ground work well though. You don't really need to know exactly where it is, just need to get the right "feel".

On asphalt what I am looking for when I adjust the springs and roll center is a particular "feel" to the car. I can see it rolling in the corners a bit. This gives you good initial cornering grip. If you make the car very stiff you won't see it roll and it wont grip as well. You can see the corner of the air dam getting close to the ground. It might need a clearance cut. You will see some scratches on the bottom sides of the wide Losi JRXS frame. I have put a bevel on the edges of the frame to give me more roll clearance on our track which has some waviness to it.

The first photo is a roll schematic, the second photo is of the chassis bevel.


John