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Old 04-04-2006, 05:58 PM   #166
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Track Temp 122F

I finally replaced the starter subject of this thread the front Losi LCD's on the JRXS. I have well over a hundred runs on them. They got a little loose, but were still working. Not a single failure!

GulF Coast RC Race Track was just resurfaced by Jeff in preparation for last weekends Speedline Grand Prix (Nitro) Race. There was a good turnout and new track records were set. The bumps on the straight are much reduced. The 1/8 scale Nitro cars were well hooked up although they paid a price in tire wear. This wear was reduced by dragging some large truck tires around the track with a golf cart.


I put double one-ways in the JRXS along with putting the Factory Rebuilt GTB6.5 back in. I thought this might be a good combination since the braking is fairly weak with the GTB 6.5. You really cannot use any brakes when running a one-way and rely on tire scrub to slow the car. The GTB is not as fast as the one it replaced but there were no thermal shutdowns. I was getting some regularly before the rebuild but it might have been due to a worn endbell bearing (also over 100 runs) which I noticed during dissasembly. It might still need a new magnet (rotor) as there is almost zero cogging when turned by hand unlike my previous unit.

My flexible A-arm test came at just the wrong time as bite was really high today from the high temperature and newly resurfaced layout. I had too much grip with CS 32's and too much steering still with Sorex 36's. I removed the flexible A-arms and replaced them with stock arms. I ended up running 20 lb Losi springs in front and 12.5 springs in back with the double one-ways with CS 32's. I still need a little work on this setup as the car was still loose.

I have to say that after running a locked diff running double oneways is just not as much fun. With the locked diff you can come in hard and tight and then slow a little to make a pass. This is not possible with double one-ways as the fast line with them is going to be wide. You might be faster with double one-ways though so its good to try both. Also with a locked diff, the car is not upset by tiny irregularities in the track like leaves or oily rubber balls from the weekend race

About 240 hits since my last post on this thread. Thanks. Feel free to post as well as this is not a private thread.

Last edited by John Stranahan; 04-04-2006 at 10:53 PM.
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Old 04-04-2006, 06:41 PM   #167
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John, every time I read your posts, it makes me happy I bought a JRX-S and very sad that I moved back to Detroit from Houston. Even though I lived in "Guns Point", it beats the hell out of not being able to race outdoors until late April - early May... You're killing me, but please keep it up. I greatly appreciate the wealth of information you're providing on this car.

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Old 04-15-2006, 05:13 PM   #168
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Tony-Thanks for the post. We do have a long season, but it gets plenty hot in August.


Track Temp 122F
Our track was recently surfaced so that traction is up. If you have been running one-ways you may have to make some dramatic adjustements to keep the back end from breaking loose. I tried double one-ways last week and never really got hooked up. Turn in was outstanding, but with a new surface it was too much. I finally was discouraged and went back to a locked diff and brakes. Hooked up well with CS 32's I had some thermal shutdowns of the GTB again today. It was plenty hot. I'm reducing the gear ratio in steps.

We had the exact same trouble with Lins Tamiya TRF415 MSX running double one-ways. Lin was running CS 37's and had too much front bite with plenty of tire squeal. Aparently the car does not come with a front ball diff to lockup so we could not try it. Chris was running oneways in a new X-ray T2. He was hooked up pretty well so I think we just did not try a stiff enough spring in the front or weak enough spring in the back with the double onways. We need to kill some of the front traction with the one-ways. The locked diff kills some of the turn-in naturally on coast with torque steer to the outside of the corner.

Last edited by John Stranahan; 04-26-2006 at 04:20 PM.
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Old 04-15-2006, 07:01 PM   #169
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Hi, John. How do you decide to use double one-way or front spool, what factors you will consider? Grip level, Tyre wear, traffic(slower cars). I'm going to race on a track which has a hair-pin corner after the long main straight, normally you would run spool because you can brake hard, but I was informed the track surface has good grip but tyre wear is bad also, front spool will kill the front tyres even faster(can't afford to use new tyres every run). have no idea what the local drivers are using.
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Old 04-15-2006, 08:14 PM   #170
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Caveman- A new tire is always faster, but only for 1 or two heats. We generally use good wearing tires for club racing like CS 27 and CS32 and don't worry about tire wear. So take the tire wear out of the equation. I don't think it's a factor. Both the same. Rotate fronts to the back on occasion to even the wear. The locked diff is harder on outdrives.

Here is what I notice. Running mod with double oneways is good for a highly skilled driver. You need a delicate hand on the car or you tend to spin out. You can use no brakes so the line for the hairpin can be taken off the straight but you coast for a little bit and take the turn with a wide entry, with the largest radius possible, still close to the corner marker, to keep up your speed. This line is easiest on fast mod motors. With a locked diff I take a medium line and use a little brakes. This is harder on the motor but also a good fast line on our track. There is more acceleration involved but it is a bit shorter. If you are used to driving with one-ways mod on your home track then I would start with that at the new track. Keep the locked diff and a locked diff spring setup in your toolkit which you have pretested at home. Hope this helps. Our fastest driver uses a locked diff, but he would still be the fastest with double one-ways. I am considerably faster with the locked diff (mod) because it is so much easier to drive. Stock or 19 turn I am about the same with both on a technical track.

Losi JRXS Rear Diff Screw is Too Short

The losi rear diff screw is just too short to run the new heavy duty thrust bearing and washer. It does not catch enough nylon and the screw backs out loosening the diff. I have been using locktite. I replaced my thrust washer with the old style that has loose balls between hardened non grooved washers. This frees up enough screw length to completely engage the nylon of the nylock nut. There are also more balls to spread the load. Make sure to use a new steel half nut for reliable service. The steel nuts are cheap from the Great Plains wall at the hobby shop.

Measuring Spring Tension
I was asked if I had a device to measure spring tension. Well I actually do. On the Losi JRXS all the springs a black (I hate this). You can sort them by the wire diameter with your dial caliper. If they have the same number of coils the smaller wire is less stiff. There is actually a formula to calculate spring rate from number of coils diameter of wire and diameter of coils, but thats another story.

Last edited by John Stranahan; 04-15-2006 at 08:47 PM.
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Old 04-16-2006, 12:52 PM   #171
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We have made some progress diagnosing the damage to Orion V2 motors in certain crashes. John Doucakis has made a nice diagram.

http://www.rctech.net/forum/showthre...ak#post2291366

See the text of the thread in the link for two interim solutions. Remove the small o-ring next to the comm and replace it with non compressible comm washers of the same thickness, and replace the endbell bearing retaining o-ring with a snap ring (the red high temp loctite would work also to retain the bearing). At least replace the small o-ring. At least one spacer right next to the comm should be non conductive (Teflon)
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Old 04-16-2006, 08:43 PM   #172
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Default Losi LCD vs MIP CVD.... vs Yok UJ

John, can we request slightly back into title of this your thread?
Currently Yok release BD masami version, on of the key feature in their ad is blue aluminum UJ driveshaft on rear end, what do you think about this, still any more people benefit of using this UJ?
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Old 04-17-2006, 12:20 AM   #173
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Faiz-I took a look at the prototype BD at the yokomo web site. I could not find a clear photo of the rear drive axles. I suspect they are the typical single universal joint type that are not constant velocity joints. These have accelerated wear only when used on the front with a locked diff. My losi constant velocity drives (LCD's) outlasted about 10 TC3 aluminum bones (MIP drives) while using a locked diff.
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Old 04-17-2006, 01:05 AM   #174
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John, take a look this photo, taken from lem2 posting on yokomo BD forum
Attached Thumbnails
Losi Constant Velocity Drive (LCD) vs MIP CVD-bd.jpg   Losi Constant Velocity Drive (LCD) vs MIP CVD-rearbdm.jpg   Losi Constant Velocity Drive (LCD) vs MIP CVD-revtns.jpg  
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Old 04-17-2006, 09:46 AM   #175
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Faiz-That's a very nice looking U-joint (single Cardan Type) It does have the advantage of large pins. This should reduce wear and breakage. It is not a constant velocity joint, however. Yokomo makes nice cars. Thanks for posting a picture,
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Old 04-19-2006, 03:07 PM   #176
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I finally wore an LCD to the point that I was willing to cut it open, here is a picture. Notice that the center ball is integral with the bone. There is a matching socket on the stub axle. Note also that there are two sets of pins making two complete Cardan joints. This is what cancels the vibrations.

The MIP drive is at the top. The Losi LCD at the bottom.

Track Temp 132 air temp 91 (rolling blackout in all of Texas from early hot weather).
RP 36's dry

GTB 6.5 Thermal Shutdowns- I'm having Thermal shutdowns at 3.5 minutes. I don't think this puppy is going to work in weather much over 80 F. I am geared within specs. 8.0. Motor temp is within specs 160 F. I have superboosted the cooling fan with direct voltage from the battery and made a stack of the stock fan, and empty fan shroud, and a second fan. It really blows a lot of air this way, but it did not help more than about 1/2 lap. It needs, some liquid cooling of the internals. Back to brushed, so that I can race. You can get quite a bit of car setup and practice in at 3.5 minutes a run, but races are 5 minutes.
Attached Thumbnails
Losi Constant Velocity Drive (LCD) vs MIP CVD-losi-lcd-guts-004-40-%25.jpg  

Last edited by John Stranahan; 04-19-2006 at 03:22 PM.
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Old 04-19-2006, 06:00 PM   #177
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Jackpot!

That's the pic i think lots of ppl wanted to see..
Is it a steel contruction inside? It doesn't look that much larger than the MIP unit above. I wonder if there are any aftermarket options for people running different chassis?

John - is something up with your GTB unit? There was a post a while back about having it replaced? And the thermals? Are you still using 12g wire on it or the stock?
80F isn't really all that hot....

After i got my airflow sorted i didn't have any issues running my car during day where ambient got to 93F and track temps soared to 120F!!!!. Granted this was on a large track so the running might have been a little different.
I did however notice my motor getting a little "soft" near the end of the runs.

A quick blast with co2 revived it...
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Old 04-19-2006, 06:55 PM   #178
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do they still make u-joint dog bones
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Old 04-19-2006, 09:21 PM   #179
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AngryAsian-The LCD is all steel and not much bigger than the MIP CVD. It is just a little bit longer and requires some small change to the hole in the caster block for clearance. Sorry for the wait for this pic. So far the only model is for the JRXS and XXX4 off-road. It is not even available for the XXXS yet. I imagine this will change in the future.


The GTB is a remanufactured unit. I sent the old one back because I suspected a defect. The new remanufactured one behaves the same way. 14 gauge wire now. I imagine that the traction available as well as the track has something to do with the shutdowns. Traction is good now and the track was very hot 132 F. I suspect a brand new one will behave the same way. I even perforated the body with the old one trying to get better cooling. This did not help. The internal temperature just rises too fast for air cooling with the conditions of our track. It is hard on brushed motors too. I can't race with the GTB anymore!!!. We get a lot of sun with our medium high temperatures. Now exactly where is the thermal sensor. 80 f is not that hot, but that is the last time I got 5 minute runs in the JRXS. I have tried four positions for it. There are none left to try. Average amp draw is about 35 amperes.

Anthony- Not quite sure what you mean, but the yokomo outdrive in a post just above is a u-jointed bone. MIP drives work similar to these, but the pin joint in the cup is on the small side for a locked diff if the material is aluminum.

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Old 04-19-2006, 09:30 PM   #180
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Well I wouldn't recommend it but you could remove the blue wire.
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