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Old 07-11-2006, 09:13 AM   #226
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John
Used your set-up over weekend on very smooth medium grip asphalt track. In general it felt pretty good overall, just a little push which I am working on.

However, just for clarification, with your lowered ride height (5.mm) what shims are you using under the front and rear roll center pivots.

Thanks
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Old 07-11-2006, 12:17 PM   #227
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Here are some Losi JRXS specs
Thin shim is .035 inch
Thick shim is .050 inch
Turning the Roll center block over = .110 inch change (measured)

At 6.5 mm I had both blocks in low roll center position, but one thin shim in front and two shims thick and thin in back. I would have used shim to raise front and back approximately .040 inch. Now having said that I have since gradually raised my ride height back to 6.0 mm -6.5 mm as traction has fallen off a bit and also returned my roll center blocks back to the lower position. I was still getting some chassis contact. I really needed one size lighter spring with the car set down low, but did not try it so that I could keep using my long TC3 springs which I liked. The next lighter TC3 spring was not in stock locally. I was very happy with my posted setup with the traction that I had on hand at that time, so I have not changed the post.


A stadard diff responds very well to spring changes (shock tower position) to cure understeer.

Last edited by John Stranahan; 07-12-2006 at 09:54 AM. Reason: .040 should have been .140. I used shim rather than turning over block.
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Old 07-11-2006, 01:52 PM   #228
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Based upon your response it would appear that you are back to square A, Low Roll Center Blocks with thin shim in front and thick/thin shims in rear.

You mention that flipping roll centerblocks over = .040 change. I remeber reading somewhere, I believe in JRXS Manual that dfference between high & low blocks was .110. I know I'm an old fart but I remeber that number pretty vividly, whre does the discepancy lie.

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Old 07-11-2006, 02:31 PM   #229
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FYI, I actually measured .090 from high to low block.
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Old 07-11-2006, 03:42 PM   #230
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Forgot to add a .1 when I used the dial caliper this morning. I measured the ammount of plastic on the side of the hole with the most plastic and got .140. not .040. This means that I used shim (probably a .035 inch) to raise the roll center rather than turning the block over. Sorry for the mistake and bad memory. I'll get a closer measure on that block.

I am back to square one almost. I am using 12.5 lb springs due to presence of some dust when I practice. On the weekend a little more spring tension is better as the track gets a nice blue groove.

I measured .415 and .305 turning over the pivot blocks. I measured to the top of a bare hinge pivot from the bottom of the chassis. Difference is .110 Thanks for catching this error. I'll correct my post.

Last edited by John Stranahan; 07-11-2006 at 04:24 PM.
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Old 07-12-2006, 06:37 AM   #231
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John,

In an attempt to fit Assoc. Springs on front I found that I ran out of shock shaft space in that It didn't seem to have enough adjustment play for droop &/or ride height. Am I missing something? I will try again this evening as it was getting late last night and I had to quit.

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Old 07-12-2006, 09:52 AM   #232
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I cut a little from the top of the shock ends with an X-acto knife to increase the space for the longer springs. No durability problems. Note that I use the original A-arms also.

Last edited by John Stranahan; 07-12-2006 at 10:33 AM.
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Old 07-12-2006, 01:51 PM   #233
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John,

I'm using new A-Arms. Would this make the difference. I'm not home right now so Ican't check this but will as soon as I get home.

Thanks
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Old 07-12-2006, 02:02 PM   #234
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Could be a whole different handling car with new arms. Do you think I need to go back to old arms to experience full benifit of your set-up?
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Old 07-12-2006, 03:59 PM   #235
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With the new arm setup it is not easily possible to fit a tc3 length spring on. The bottom shock mount needs to be cut down already to allow for proper shock operation with rubber tires or larger foams. Chances are you will not be able to get the right ride height unless you take off the threaded collar and use plastic preload clips.
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Old 07-12-2006, 05:27 PM   #236
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John
I agree with RC racing kid. I would forget the longer springs with the new arms. The new arms have the bottom shock pivot slightly farther out as well as higher. This would require slightly softer springing as well as shorter springs. Stick with the short springs and try the Losi 12.5 or the Losi 15lb springs. I would get both. If you want to try your TC3 springs later, get a set of the original arms and trim the shock end.
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Old 07-13-2006, 04:09 PM   #237
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Air Temp 97 F Track Temp 127 F (partly cloudy)
GTB 6.5 geared 7.55, RP 36 dry

Alcohol cooling test of GTB 6.5 motor.
It was plenty hot and a good day for this test of what I will call my "blown alcohol motor". I put 2 caps of alcohol on my sock from the bottom of the car with the car buttoned up just before a run. This immediatly cooled the motor 10 degrees. I was able to run 3 full packs for a full 7 minutes Each. I could not do this even in the winter with 7.55 gears. Performance was great. I had a nice blue groove to practice in with a couple other racers. I had good traction to work the motor hard. Maximum motor temperature was 150 F. Both temp sensors are hooked up so the problems that I have been having are motor overheating rather than speed control overheating. The speed control fan was wired stock. I am glad to be rid of my extra useless fans. The Losi was really hooked up by the end of the session.

Effects of alcohol should be no more harmful on the motor than cleaning a brushed motor with motor spray. It does not get on the motor bearings. No real hazards involved with 70% rubbing alcohol. The sock is not that pretty, but neither is a couple hundred dollar item sitting in the pit bag. Use a red sock or a black sock. Some cotton in the fabric is probably good. I'll await the velcro on model that I can buy off the shelf.

The photo shows the bottom of the motor this time and the trim I made at the track for clearance on the bumps. It also shows the extra rings of cloth where the trim ring used to be on the motor.
John
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Losi Constant Velocity Drive (LCD) vs MIP CVD-cooling-sock-bottom-cropped.jpg  
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Old 07-13-2006, 09:37 PM   #238
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John - What do you think if sock replaced with chamois?
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Old 07-13-2006, 10:20 PM   #239
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Faiz. Chamois should be good or even synthetic chamois. You should be able to make a tighter neater package. The Losi JRXS has a pretty low clearance between the top plate and the motor so it might not fit this car. The sock compresses under the cross braces. Other cars have more room. Tell me if you get some results. Expect some very light staining type of corrosion of the bare steel of the stator under the trim ring. I think it is inconsequential. I would certainly remove the trim ring to cool the stator stack directly. I'll pop the motor open after a couple more sessions to peek inside. I might try some 90% ethanol type of rubbing alcohol at a later date. This would reduce the staining.

John

Last edited by John Stranahan; 07-13-2006 at 10:33 PM.
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Old 07-19-2006, 04:35 PM   #240
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Air Temp 100 F Track temp 142F

Alcohol Cooling

I ran four packs through the GTB today. It was was hot hot hot. Not as hot as possible here (108F air temp), but hot for July. I got plenty of run time using the alcohol cooled GTB 6.5 motor. See pictures above of the motor cooling setup. The maximum motor temperature was 167F with one of the 4200 packs that had more than 6 minutes run time before the motor thermalled (the car stopped). It was already a slow lap though. A good place to get this temperature is one of the T-nuts on the back cover that are pretty close to internal temperature. The black cover is 15 degrees cooler.

Now what about the 4.5. Well I think that if I cooled it, the speed control would probably still thermal on a hot day as it's bound to work harder in spite of lower gearing. I might test this later when funds permit.

On one run I tried to see if I could run two packs back to back. The speed control thermalled early on in run number two by running slow. Speed control temperature was 147 F, so cool this puppy to ambient temperature before your run again.

Now is running this motor with the need for cooling better than cutting the comm every run and buying new arms every 10 runs or so, well, I think it is. The motor is setup to run as fast as any brand of 10 x 1 brushed motor.

JRXS

This pretty much finishes up my long term test of the Losi JRXS, GTB 6.5 and Scorpion Lipo. The losi is performing well and is quite durable and easy to work on now that I have learned the tricks. The chassis will stay tweak free only if you put locktite under the heads of all the screws that contribute to chassis torsional rigidity. The only thing I would like is longer A- arms for when the track is slicker, but this would require a whole new car. Chassis tweak is a problem on most of the double plate chassis cars that have the bulkheads in two pieces.
A simple design change to a square based bulkhead like on the FTTC4 would eliminate the tendency for the chassis to tweak. On the FTTC4, the square base is neccesitated by the gears but it would be easy to incorporate into other designs. What the base would do is prevent the two bulkhead halves from going askew on severe impact.

Scorpion
The scorpion LiPo is still working well. It is fast as hell for mod. I can only run it once per practice session due to the long charge time, though. I saw that Sony had some LiPo's in the making with 3 minute charge times!!!! great for the power tool market and maybe us.

Novak GTB 6.5
The GTB works great with extra cooling. Air cooling was not of much help. The alcohol helped a lot with few downsides except appearance.

Last edited by John Stranahan; 07-27-2006 at 09:12 PM.
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