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Old 11-22-2005, 08:32 AM   #1
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Default Losi LCD's vs CVD's, JRXS, Novak GTB

Losi Constant Velocity Drive vs MIP CVD
First the question and then some background material. Have you used the Losi Constant Velocity Drive axles (LCDs) on the front end with a front spool. See the photo below. How do the LCD and outdrive parts hold up compared to using a MIP CVD.
The standard type of crossed Universal Joint, like you see at the end of a driveshaft near the rear differential on a full size pickup, is called a Cardan joint. If a single Cardan joint is used on a drive axle and the axle runs at an angle, then the axle actually accelerates and decelerates four time per revolution. On a pickup this vibration is taken up by a second single Cardan Joint near the output shaft of the transmission. If the output shaft angle of the transmission and differential input shaft angle are close to the same, which they are from the factory, then the two Cardan joints exactly cancel their vibrations. On an RC touring car, this small change in the rotational movement of the drive axles (vibration) is usually taken up by motion of the ball differential which transmits the motion to the axle on the other side and to the driveline. This does a good job of dissipating the excess vibration, especially if you have a belt drive. The MIP CVD shown in the Bottom of the photo is actually just a well made single Cardan type joint. It is not a constant velocity drive at all.
When you run a spool on the front ( a solid diff that does not allow any slip), the vibration becomes a big problem. The diff no longer absorbs the vibration and the inner dogbone pin rocks back and forth in the drive cup slot. Rapid wear of these parts result. I once bought an aluminum spool for the front of TC3 and used it with standard dogbones. The pins ate the spool up in 3 battery packs. Very disappointing. You need to run pin pillow type dogbones to help, but then you have constant problems of bending the tinier pins.
I now have a new Losi JRXS kit in hand. The kit comes with two of what they call a Losi Costant Velocity Drive or LCD. This is a double Cardan Joint. It is a true constant velocity drive and should not suffer the vibration problem when running a spool. A spool is still going to tear up your axles in a crash (compared to a ball diff), but the inner dogbone pins should not wear the outdrive. I have a Novak GTB 6.5 speed control to thrash this Losi with. Ill give my reports on the JRXS, Novak GTB 6.5 in this thread at a later time.

there is another photo showing the LCD dissasembled Here

Here is a photo of a Yokomo single Cardan joint posted later in this thread.
http://www.rctech.net/forum/showthre...m2#post2294284
Attached Thumbnails
Losi Constant Velocity Drive (LCD) vs MIP CVD-losi-lcd-mip-cvd.jpg  

Last edited by John Stranahan; 04-20-2006 at 10:44 AM.
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Old 11-22-2005, 08:49 AM   #2
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the triumphant return of john stranahan. let us know your findings, sir.
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Old 11-22-2005, 11:36 AM   #3
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Default Masses

Here are some weights.

Losi steel constant velocity drive 9 grams for one drive axle. Here is some detail. The center tube is steel and is drilled for two crosspins making the double joint. There are two balls inside the joint, I presume on center to keep the joint from being floppy. The pins are secured in place with Heat shrink tubing which you see on the photo. The joint came assembled so I do not have ready acces to the insides. The Picture on Losi's site and in the mags is not very good at letting you see the detail. I guess dark is in. The joint is very similar to the double Cardan joint found on the front of the driveshaft of my old full size ford Bronco. On this truck the Diff input shaft is lined up straight with the driveshaft, so the rear Cardan joint produces no vibrations.

Losi (MIP) Aluminum Dogbone CVD Drive axle 6 grams. I have gone through a handfull of these running 19 turn class.

Associated (MIP) CVD with anodized Aluminum Dogbone. 6 grams. This one weighs the same as the Losi Bone. The Losi bone is a larger diameter.

Associated (MIP) Plastic Dogbone CVD 5 grams. This one works great on the back of the TC4 for stock. Although it is one inch longer it weighs 20% less than the Associated and Losi Aluminum Dogbone and this is rotating weight. No good for mod.

Seaball thanks for the welcome. Always good to have another gearhead look over my posts.
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Old 11-27-2005, 07:21 PM   #4
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Default [B]Losi JRXS Assembly Tips[/B]

I am still interested in a reply to my initial querry. How are the Losi LCD's holding up for you?

Losi JRXS Assembly Tips

In the meantime. I have my Losi JRXS kit assembled. Here are some tips that I have learned through racing to reduce the number of agonizing Did Not Finishes (DNF's).

Put #4 Washers under the fasteners that hold on the Shocks. If a shock pops off a ball in the race you will not finish. Make sure the shock rotates easy on its own axis when you turn the body with your fingers. In other words, make sure the pivot balls are not binding.

The outer hinge pins have double fasteners, but if you decide to just use the centered securing set screw tighten it a little at a time then push on the end of the pin. If the pin slides then tighten a little more. This procedure keeps you from stripping the plastic, as the screw has very little feel when it bottoms. A lost pin = DNF.

I usually have the same shock setup on the both fronts for touring car races on a road course. I used the shocks with a single dot on both fronts. I have seen a racer with a mixup here. The car did not handle well.

If you run low roll centers on the back, swap sides on the rear roll bar mount/ uptravel limiter. I am setup with low roll centers to run on a dusty outdoor track.

I had three ball cups that, when pressed on, would not move freely. I replaced the three. I made sure that each arm with the shock disconnected would move freely up easy and down by gravity alone.

The XXXS Rear hubs are the same as JRXS. I used 1/2 degree XXXS hubs and 2 degree inner pivot pin mounts on the rear to give 2.5 degree of rear toe for running mod. Might end up needing 3 degrees. I'll test it first.

Initial Reactions
I could have used a bit more chassis width to mount this chunky brushless speed control. Instead I used the sensor wiring loom as a bumper for the side of the speed control.

I wish Novak would put a flatspot on their power capacitor so that you could mount it firmly with Servo tape. This new type with a small Printed Circuit Board is a little better in this regard.

The car came with center and front one-ways. I was expecting some kind of locked front diff as well. No luck here. There is a spool for the center drive pulley.

Assembly was easy. I'll put it on the surface plate later and see how flat the chassis came out, and then, at a later time, I'll test to see how flat and stiff it is staying.

Here is a pic of the Novak GTB 6.5 Brushless System installed in the car. I am experimenting with different leadless solder right now. This is 2 percent silver and 98% tin at the motor. It does not flow very well. The wires are only 14 gauge, but there are three of them and this gauge is well suited to mod.
Attached Thumbnails
Losi Constant Velocity Drive (LCD) vs MIP CVD-novak-brushless-system-70%25.jpg  

Last edited by John Stranahan; 11-27-2005 at 07:40 PM.
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Old 11-27-2005, 08:04 PM   #5
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Quote:
Originally Posted by John Stranahan
I am still interested in a reply to my initial querry. How are the Losi LCD's holding up for you?

Losi JRXS Assembly Tips

In the meantime. I have my Losi JRXS kit assembled. Here are some tips that I have learned through racing to reduce the number of agonizing Did Not Finishes (DNF's).

Put #4 Washers under the fasteners that hold on the Shocks. If a shock pops off a ball in the race you will not finish. Make sure the shock rotates easy on its own axis when you turn the body with your fingers. In other words, make sure the pivot balls are not binding.

The outer hinge pins have double fasteners, but if you decide to just use the centered securing set screw tighten it a little at a time then push on the end of the pin. If the pin slides then tighten a little more. This procedure keeps you from stripping the plastic, as the screw has very little feel when it bottoms. A lost pin = DNF.

I usually have the same shock setup on the both fronts for touring car races on a road course. I used the shocks with a single dot on both fronts. I have seen a racer with a mixup here. The car did not handle well.

If you run low roll centers on the back, swap sides on the rear roll bar mount/ uptravel limiter. I am setup with low roll centers to run on a dusty outdoor track.

I had three ball cups that, when pressed on, would not move freely. I replaced the three. I made sure that each arm with the shock disconnected would move freely up easy and down by gravity alone.

The XXXS Rear hubs are the same as JRXS. I used 1/2 degree XXXS hubs and 2 degree inner pivot pin mounts on the rear to give 2.5 degree of rear toe for running mod. Might end up needing 3 degrees. I'll test it first.

Initial Reactions
I could have used a bit more chassis width to mount this chunky brushless speed control. Instead I used the sensor wiring loom as a bumper for the side of the speed control.

I wish Novak would put a flatspot on their power capacitor so that you could mount it firmly with Servo tape. This new type with a small Printed Circuit Board is a little better in this regard.

The car came with center and front one-ways. I was expecting some kind of locked front diff as well. No luck here. There is a spool for the center drive pulley.

Assembly was easy. I'll put it on the surface plate later and see how flat the chassis came out, and then, at a later time, I'll test to see how flat and stiff it is staying.

Here is a pic of the Novak GTB 6.5 Brushless System installed in the car. I am experimenting with different leadless solder right now. This is 2 percent silver and 98% tin at the motor. It does not flow very well. The wires are only 14 gauge, but there are three of them and this gauge is well suited to mod.

I have raced the entire outdoor season with the MSRA in Mmephis this year on the original set. I did however use the rebuild kit 2 weeks ago in preparation for the indoor season. The LCD's had slop in them and after rebuilding them they still have the same slop. On closer inspection the only play left in the LCD is coming from the axel. I have now replaced the axel too and the slop is Zero again. After this rebuild experience I know feel like I should keep a rebuild kit for an emergency like loosing a pin or the shrink tubing. But I will also keep a complete set ready to replace the worn set as rebuilding them seems silly. Hope this answers your question. OH and BTW--I have run a spool all year with the exception of the first race day on the JRXS.

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Old 11-27-2005, 08:42 PM   #6
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my left LCD has twice the slop my right LCD has...must be those darn sweeping corners and that spool
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Old 11-27-2005, 08:45 PM   #7
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Quote:
Originally Posted by R/C Anonymous
my left LCD has twice the slop my right LCD has...must be those darn sweeping corners and that spool
Mine were equally sloppy but I did break 3 right arms and 2 right outdrives this year! Maybe this made mine both equal? LMAO

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Old 11-27-2005, 09:44 PM   #8
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POOKYT, R/C anonymous - Thanks for the replies. Sounds like the LCD's are holding up pretty good even with a spool. It looks like from your posts that the spool will still cause accelerated wear probably because the bones don't accelerate smoothly in the outdrives even though the LCD's have smooth rotation. The less the angle of the outdrive to the bone the less this problem will be. You do have a choice of high or low diff height.

Chassis flatness, Chassis Tweak

I measured the flatness of the bottom chassis plate by putting the car on a couple of parallels on a surface plate (very flat granite plate). The twist in the chassis was less than .001 inch. Very good. I put a moderate twisting force on the chassis with the chassis in my hands and remeasured. Still flat. Good so far.

Double plate chassis have some problems with chassis tweak after some use. This means the chassis gets twisted in a crash and stays twisted affecting handling. This happens as the screw holes enlarge with use. The pinned plates on the Losi chassis are supposed to prevent this. I'll retest after some hard use. The TC3 has a severe problem with chassis tweak if you leave a hot motor in it after a run. This eventually pulls the right rear corner upward. Take that motor out after each run on the TC3. The new TC4 and factory team TC4 should not have this problem because of the Aluminum Motor Mount. The TC4 motor mount is similar to mods I made on my TC3. The Losi XXXS chassis does not tweak at all even with a hot motor left in all the time.

Last edited by John Stranahan; 01-04-2006 at 11:17 AM.
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Old 11-28-2005, 04:32 PM   #9
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Default Losi XXXS vs JRXS chassis Rigidity

Losi JRXS Chassis Torsional Rigidity

One of the things that makes for a predictable handling race car is rigidity in the chassis. Some cars, like the HPI with a molded chassis, have very poor rigidity. It is easy to twist the chassis. The HPI does not respond well to tuning on a high grip track by changing the springs on the car. The Losi XXXS is also a molded chassis, but because of the center box tube, it is fairly stiff. This means if you pick up the car grab the front and the back and try to twist it, the chassis resists strongly. The XXXS responds very predictably to tuning.

I thought I would measure the stiffness of the new Double Plate Woven Graphite Fiber chassis of the Losi JRXS and compare it to the older Graphite Molded Chassis of the XXXS. I used a fairly elaborate setup with the back end of the car in a milling machine vise and the amount of twist measured with a dial indicator on a bar mounted to the front. The numbers are in. The New Losi JRXS is about 2.5 times stiffer than the old XXXS chassis in torsion. I'll see if it stays that way. The calculated numbers are 1.78 Newton-meter/degree (N-m/deg)for the Losi XXXS and 4.34 N-M/deg for the Losi JRXS. I was actually surprised that the new car was stiffer.

On the Associated Factory Team TC4 this torsional stiffness is adjustable.

Last edited by John Stranahan; 11-30-2005 at 12:36 PM.
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Old 11-28-2005, 05:48 PM   #10
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Hey John! Glad to see you are still providing great info as usual!!
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Old 11-29-2005, 03:29 PM   #11
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promatchrcr-Thanks

Loctite

I wanted to test the LosiJRXS chassis stiffness as is, right after assembly. Then I wanted to secure certain screws a little better. I removed all the top and bottom chassis screws that mount the top plates to the bulkheads and bulkheads to the chassis. I added blue Loctite near the head. The purpose of this is twofold. First the locktite around the head is enough to keep the screw from loosening. The holes in the chassis will tend to elongate faster from crashes if these screws come loose. (I noticed that in the JRXS thread advise was given to check these screws before a race.) A second purpose of the Loctite is that it fills the area between the screw shaft and the hole in the top plate. This effectively creates another pin.

Spindle Carriers/Caster Blocks

The Carrier (caster block) is secured to the Spindle (knuckle) with a long ballstud on top and a button head screw on the bottom. As you knock into things this top ball stud eventually gets loose. Then it starts to bend. Then if fails usually ruining the knuckle. You can prevent this by adding blue Loctite to the upper portion of the ballstud threads. When you tighten the ballstud the locktite will get hard and form a tight fitting cylinder out of the top portion of the ballstud threads inside the bushing. This cylinder as well as a thin layer that will ooze out under the bushing flange will make the ballstud much more solid. It won't loosen, bend, or fail as easily. I learned this trick racing the Losi XXXS. The outside of the bushings needs to stay free of locktite so that the knuckle can pivot.

Note that I have been told that locktite will damage plastic parts. The only plastic that I have seen it damage is a clear plastic gear cover on a losi truck. The black plastic in the frames and other parts are undamaged. I have lots of experience here. I doubt the other fellow had even tried it.

If a screw secured with Loctite is ever difficult to remove heat it for 3-5 seconds with your soldering gun tip. This will liquify even the red Loctite and allow easy removal. The plastic is undamaged.

Last edited by John Stranahan; 11-29-2005 at 03:53 PM.
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Old 11-29-2005, 03:57 PM   #12
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John - The Losi LCD is what is commonly called a double hook joint. It functions as a true constant velocity drive whereas MIP and all other units called CVD's are really just rebuildable universal joints. The MIP and all other CVD's and universal joints are the cause of the chattering guys get when running spools. The LCD stops this completely.
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Old 11-29-2005, 04:54 PM   #13
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John,

Interesting read! With regards to chassis torsional rigidity, you may want to run the test again, but with the rear upper deck standoffs removed. It is common for people running rubber tires to remove these 4 standoff posts to make the chassis more flexible. It generates more grip and is easier to drive. I know when I twist the car in my hands, it is more flexible without the posts than with them installed, but it would be cool to see you put some hard numbers on that difference. Just something to think about, if you're interested. Have fun with the car!
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Old 11-29-2005, 06:25 PM   #14
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AdrianM-Thanks for the post. I see that we are in agreement on my first post except on the name of the beast. I'll look into it. Double Cardan Joint or Double Hook Joint.


Juan- I still have the stuff on the milling table. It is some trouble, but I will look into getting a number. Thanks for the tip on adjusting the Losi JRXS chassis Rigidity.

Here is a link with some diagrams of driveshafts (full size) using a cardan joint on each end vs a driveshaft using a Double Cardan Joint at the transfer case and a single cardan joint at the rear diff.

Two single Cardan Joints vs Double Cardan plus Single Cardan

I'll note that Losi used to sell a constant velocity drive axle for the truck. It was not advertized as such. It had a single cardan joint on each end and a slip joint in the middle. Similar to the first diagram in the link above. No dogbone. It was all plastic and lightweight, but the slip joint did not work as well as a dogbone sliding in a slot.
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Old 11-29-2005, 07:29 PM   #15
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Juan-here is the new number
The bigger the number the more stiff the chassis is.

Losi JRXS (Top plate Posts Removed)=1.2 Newton-Meter/degree (N-m/deg)
Losi JRXS (Complete)=4.3 N-m/deg

Removing the posts cut the torsional rigidity by almost a factor of 4

Losi XXXS (Complete) 1.8 N-m/deg
Very close to the new chassis with the posts removed.

Last edited by John Stranahan; 12-22-2005 at 07:07 PM.
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