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Old 11-10-2009, 05:52 PM   #91
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Quote:
Originally Posted by fathead View Post
Can somebody with a xxxs please measure the centre to centre distance of the diffs on a xxxs.
259mm
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Old 11-10-2009, 05:56 PM   #92
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Quote:
Originally Posted by da_John_wee View Post
25.9mm
Sorry I should have been clearer, the distance from the centre of the front diff to the centre of the rear diff, unless you mean cm and not mm?
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Old 11-10-2009, 06:05 PM   #93
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Originally Posted by fathead View Post
Sorry I should have been clearer, the distance from the centre of the front diff to the centre of the rear diff, unless you mean cm and not mm?
look again sorry for that confusion, been along time since I used mm
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Old 11-10-2009, 06:06 PM   #94
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Magic!!

Thanks for that.
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Old 11-10-2009, 07:03 PM   #95
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Originally Posted by John Stranahan View Post
The low roll centers should help prevent traction rolls by preventing the "suspension jacking" up in the corners. You should combine this with stiff springs and sway bars to have a high roll stiffness and promote sliding.

The XXX-S came in second in the big race. We started 7 guys in the main. It was only 62 F and cloudy this morning so I softened tires to Sorex 36R. This was a mistake with the 3.5 motor and my lap times were off. The XXX-s made the 6 heats with no damage except to the one tire bead.

Good work John

nice too hear the car ran sweet all meet
so what's ya overall verdict of this car compared too the others you've ran previously

Rob
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Old 11-10-2009, 08:45 PM   #96
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This race was pretty severe duty for a Touring car. Motors are 3.5 or 4.5. Traction was good. Track Temperature for 5 heats was 105F or so. The track is long the speeds are high. So here is a little score card on durability.

Losi XXX-S- finished 6 of 6 with the most powerful drivetrain of the bunch.
In my best heat I was within 1/2 lap of the leaders TQ.

X-ray T2 equipped with a 3.5, 3 failures of the rear ball diff. One other failure. Only completed 1 of 6 heats.

A second X-ray T2 lost two rear belts. Finished 1 out of 6 races.

Serpent S20. Only finished 1 of 6 heats. Rear out drives on the gear drive rear diff failed twice. Rear belt failed. Shock came off arm.

X-ray T2R equipped with a 4.5, this car did fairly well as it had one size smaller motor. Shock came off arm in the main, though. Finished 5 of 6 heats.

Tamiya 414, This car did fine except for the constantly thermalling electronics. Finished 2 of 6 heats. Typically this chassis has a bunch of loose screws to deal with after a little use.

Only speed controls that worked with 3.5 motors. LRP TC edition (pre SXX), And Tekin RX8

If we had not had a unusually cool cloudy day at 62F (62F track temps) for the main the Losi would probably would have passed a thermalled first place Tamiya 414 even with my poor selection of tires.

Results of course may have been different if I owned one of the above chassis. I also ran my Associated TC5 with similar power for 2 years with little trouble.
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Old 11-11-2009, 10:57 AM   #97
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a Great accomplishment with a RTR car, I don't think any one have or even tried this before. Good Job John.

Quote:
Originally Posted by John Stranahan View Post
This race was pretty severe duty for a Touring car. Motors are 3.5 or 4.5. Traction was good. Track Temperature for 5 heats was 105F or so. The track is long the speeds are high. So here is a little score card on durability.

Losi XXX-S- finished 6 of 6 with the most powerful drivetrain of the bunch.
In my best heat I was within 1/2 lap of the leaders TQ.

X-ray T2 equipped with a 3.5, 3 failures of the rear ball diff. One other failure. Only completed 1 of 6 heats.

A second X-ray T2 lost two rear belts. Finished 1 out of 6 races.

Serpent S20. Only finished 1 of 6 heats. Rear out drives on the gear drive rear diff failed twice. Rear belt failed. Shock came off arm.

X-ray T2R equipped with a 4.5, this car did fairly well as it had one size smaller motor. Shock came off arm in the main, though. Finished 5 of 6 heats.

Tamiya 414, This car did fine except for the constantly thermalling electronics. Finished 2 of 6 heats. Typically this chassis has a bunch of loose screws to deal with after a little use.

Only speed controls that worked with 3.5 motors. LRP TC edition (pre SXX), And Tekin RX8

If we had not had a unusually cool cloudy day at 62F (62F track temps) for the main the Losi would probably would have passed a thermalled first place Tamiya 414 even with my poor selection of tires.

Results of course may have been different if I owned one of the above chassis. I also ran my Associated TC5 with similar power for 2 years with little trouble.
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Old 11-11-2009, 05:44 PM   #98
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Thanks-

Track Report. Track Temp 105F

I had some luck today. Phil (from the shop)was practicing and had the lap timer on calling out lap times. This is ideal time for testing and trying out different race lines on the course.

Roll Stiffness
First test. I increased roll stiffness front and back by moving the top of the shocks out four holes to the outboard position. Lap times were good except that I made a big mistake once in a while on the chicane. I had dialed myself out of my safe sweet spot. I put the springs back all the way in. I am having no difficulty there just need to go a bit faster.

Kickup
I tried 4 degrees of kickup this time instead of 2 degrees. Maybe I would notice a change. Now this is part of what kickup does, when the wheels drive the arms forward, the arms are tilted up in front, this also drives the arms downward; it makes the front suspension stiff. If you are powering out of a corner with a locked diff, you should get more torque steer. If you have a standard diff you should feel the cornering traction at the front ease up and let the front wheels slide out preventing oversteer. In contrast on deceleration the arms are driven upward making the suspension soft. You should get more turn in as a result.

This is what I noticed. I now had spins in the chicane and on the second half of the sweeper which had been trouble free. I tried to notice more acceleration or steering on corner exit, but could not. I could hear that the suspension seemed harder and the tires were making more noise on the pavement negotiating roughness. Lap times were not improved even for a few of them. I took it back out.

Gearing, Motors
I ran with an LRP X 12 4.0 geared 90/26 with the Tekin RX8. The motor came out a little hot (178F) whereas with the Tekin RSPro temp was OK for the same motor with this gearing. I geared down to 90/25 and ran the best fast laps of the day. Note the Tekin RSPro is prone to thermalling itself.

I ran with a LRP X12 3.5 geared 88/21. This was 1/2 tooth lower than my race gearing in the Grand Prix. I got not the lowest lap times but the longest number of laps with a low lap time. This is what I will race next Sunday. Temps were high but still good at 175 F after 6 minutes. This higher temp than during race day showed I was getting a better tire hookup than during the race.

I tested a more flowing line after the chicane and was rewarded with .2 seconds better laps each occurrence.

I am at 52.8 ounces with the Tekin RX8 This is good for a stiffzell car. Unfortunately I adopted a 1425 gram limit or 50.2 ounces which was adopted by the international indoor champs for rubber tired cars. I have a Graphite plus coming to see if I can get a little closer to 50 ounces.
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Old 11-13-2009, 10:52 AM   #99
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Protoform LTCR body
The body finally came in. With no paint or decals it did indeed lighten the car by 1 ounce. But with paint it gained .3 oz. I am at 52.1 ounces. Test later today. The fit was good to the lengthened wheelbase. The wing comes oversize. It needs to be trimmed for a ROAR race. One racer noted lack of steering as a result of the big wing. He trimmed and perforated it and had good steering again.
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LOSI XXX-S, Tips and Tricks, Open Mod, etc-protoform-lt-cr-bocy-001.jpg  
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Old 11-21-2009, 09:19 AM   #100
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Weight Reduction Continues. 51 ounces achieved.

The weight reduction continued in very small very expensive steps. First a complete set of Lunsford stuff which is readily available. Hinge pins, turnbuckles, Upper shock mounts. This all was worth .3 ounce reduction.

Next a Graphite plus chassis and a dozen or so more Aluminum screws. The used car I purchased had just a few graphite parts. The chassis was worth .3 ounce reduction. This includes a sawn off right side rail for LiPo battery clearance and the extra screws. Note that my stiffzel chassis was already pretty light from G+ like cutouts.

Spotters guide.
There are at least two versions of the G + chassis. This last version has the most radical cutouts near the steering links. There is also a lightened section underneath that is made by milling with a 1/4 inch bit after the chassis is molded.

Next a little trimming. I decided to used taped battery and inner side rail so that I could get my weight balanced just right without ballast. From the pic you can notice the battery edge is just outside the rail. LEXAN sheet or the sawn off rail edge can be added for T-bone protection if desired. I removed the forward battery strap support cross brace. I added a thin graphite inner battery support rail. I made a minimal size rear bumper. This was worth a .2 ounce reduction.


This achieved 51 ounces. The weight limit we adopted was 50.3 ounces or 1425 grams (from the International indoor champs for rubber tired TC)
This is about as light as I can make the car with the 1/8th scale speed control. If the new CRC "Black Diamond" speed control will handle a touring car this will lighten the car to spec.

The used car came with the blue belt which I will try next. It had the good hard oudrives with saver ring. These I already had in front and are wearing very good. The original RTR oudrives are on the lightly loaded rear and have a good divot already worn in place. It also came with G+ front arms and 4 degree C-hubs (caster blocks). I will try this next. Some aluminum bones might be OK in the back. The car came with one good set.
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Old 11-21-2009, 11:55 AM   #101
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whats the value of that cap you have on the speedo? what voltage...micro frd? (spelling)
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Old 11-21-2009, 07:20 PM   #102
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Nomaak- That cap would be this one. 8200 uF

http://www.teamnovak.com/products/di...power_cap.html

It is supposed to help the speed control run cool. Tekin recommends two caps. I just used a large cap.


Weight reduction
So why go to the expense to meet minimum weight. I lost 3.5 ounces. That's 6.5% less weight. Acceleration is inversely proportional to weight.

I would accelerate 6.5% more slowly with the same power at the heavier weight.

Rubber tire to asphalt cornering power increases with lighter weight as explained earlier.

I should have more g's of cornering power. Every little bit helps on a race car. 3.5 ounces on a touring car is huge.

Next a possible rotating mass change to the rear drive axles. There is a two fold improvement there. Less mass on the car and at the same time less mass to rotate. I'll see if some aluminum bones will hold up in the rear.
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Old 11-22-2009, 07:44 AM   #103
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These are answers to some questions by PM (I added a few words)

I think you will find a fan as good as the heavy heatsink fan. I trimmed my Integy heatsink until it was just a fan holder like you state. The motor is cool with the LRP fan driven at pack voltage. This is a good way to reduce weight.

I like my battery mod. I think putting on the inner fence to hold a cross strip of tape is essential. I have made the same mod to the new chassis.

I notice you are up against that same 1425 gram limit. I have reached it with a normal speed control so there is hope in sight.

I absolutely like the front clutch type diff from the JRXS on the XXX-S. Wear and breakage are minimal.The clutch action is what helps prevent breakage here. If you lock it it will break. Wear is very good with a 3.5 even. Don't mess with it. I pioneered the clutch diff in my previous thread. A ring reinforced outdrive is a must up front.

You can try aluminum dogbones in the rear. Front and rear if running stock. Redrill those aluminum cups at the CVD end of the dogbone when they get worn. I used to put up to 6 holes in them. Use extensive chassis cutouts if you have the RTR chassis. Use the G + chassis as a pattern or a guide. That green belt and tensioner are a few grams lighter than the black belt and long tensioner.

I am at 51.0 ounces with the heavy RX8 speed control and steel bones all around.
John
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Old 11-22-2009, 11:07 AM   #104
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do you think the RTR components are too soft for parking lot racing? or is it juuust enuff flex to generate traction on the unprepped surface? i currently dont run as much horsepower u run (8.5BL / 19 turn br) but as tiny as our track is....big motors aint much of an advantage anyway.
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Old 11-22-2009, 12:38 PM   #105
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John, I was just wondering what you set out to accomplish with the XXX-S? Why didn't you just use an updated design like the JRXS-Type R for balance and lighter weight? DO you feel the single belt XXX-S has an advantage over the newer TCs using a two belt design? Just curious what you think of a updated XXX-S or a double deck design? I love the XXX-S, but it does lack some of the fine tunning adjustments over newer designs. Is there anything you would change, I'm curious as to what you think pros and cons of the XXX-S. Also, I thought a set of Ti screws helped getting my XXX-S weight down. Thanks

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