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Old 10-28-2009, 06:22 PM   #1
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Default LOSI XXX-S, Tips and Tricks, Open Mod, etc

Losi XXX-S Tips and Tricks for Open Mod. etc.

This thread follows a long list of my threads on RC-tech.net. It is not meant to replace the 1000 page Losi XXX-S thread also on this website. The thread will be tech heavy as befits RC-Tech. As in all the the following threads there will be give and take. I hope to learn new things from the readers as well as give out some of my own information. Here is a list of my previous threads. Where a link is available they are still archived here on RC-Tech. All contain plenty of good color photos.

Losi XXX-s Tips and Tricks for Stock (no longer archived)
Associated Factory Team TC5, Brushless, LiPo, Li-ion Nanophosphate, Tips and Tricks
Losi LCD's vs CVD's, JRXS, Novak GTB
Pantoura, 1/10 pan car, 2S LiPo, tips and tricks.
Associated Factory Team TC5 Tips and tricks
CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo, 4c, Road, Oval,Tips and Tricks

First I shall answer the question why change cars at this point and why the XXX-S. I have been driving the Associated TC5 which is a double plate (chassis and top deck), double belt car. I have no complaints really. It performed admirably in our last open mod race at Mikes-HobbyShop.com. This track has recently been resurfaced for the 2010 1/10 Nitro Sedan IFMAR worlds. The straight is almost 240 feet long with a fast chicane at the beginning. The TC5 was holding 3rd place after the closing buzzer until I stuffed it a few turns from the finish loop. I finished fourth.


I have often said that the zenith of mod motor touring car design was with the LOSI XXX-S. Here is why.

The pulleys are perfectly centered between equal length out drives and drive axles due to the single belt. No torque steer.

The motor is tucked in tight to center of the car due to the single belt.

The center box tube adds considerable rigidity to the frame in an absolutely tweak free molded chassis. A year later my much abused XXX-S was perfectly flat on the surface plate. Same steering left and right after a few bumps.

The motor is in a place such that motor heat does not tweak the chassis (like the TC3). A heat sink motor clamp was helpful.

Now there were some suspension idiosyncrasies which helped the car in mod, but not so much for stock.

The front arms are swept back-This was done to prevent driveline chatter on huge forward power and indeed the driveline does not chatter or shudder. It either goes or smoothly slips.

The front drive axles are also swept back. There is a friction driven force on the oudrive cups that affects the ends of the axles on acceleration. If you sweep the drive axles back and accelerate there is a tendency for this force to lift or hold the drive axle steady. You can demonstrate easily by removing the shock and gunning the axle held by the finger on hub bottom (no tire). This prevented front end lift and lets the car transition from power to deceleration quickly. It is great for mod. In stock you tend to reduce front tire traction and go slightly slower.

The serpentine belt is super in most uses and not so good for high traction stock. What I found is that on outdoor stock on a low grip track that the belt would billow out from the pulleys and friction was less than dual belt cars. I could pass on the sweeper. On a high grip indoor track the traction bound the belt tightly to the pulleys and you were Ĺ lap behind the TC3s. I had both. On outdoor mod the belt is just beautiful as the long belt cushions the driveline from the grunt of the motor and applies smooth power to the tires. Improvements have been made for stock by using a more supple belt and by trimming teeth on the belt to every other tooth.

The belt tended to skip teeth on brakes. On my road course now with brakes at 45% and the HD long belt, I donít get this. That is sweet. There seems to be enough brakes at this level. At 60 percent you get the horrible sounding but harmless teeth skipping noise.

I am getting good turn in and cornering grip with the more flexible stiffzel chassis.

And on top of all this the car is inexpensive.

So much for history, now how to setup the beast.

Losi XXX-S setup Open Mod
I had to purchase an RTR as no kits are readily available. I actually wanted the Stiffzell to try for outdoor asphalt instead of the graphite plus edition. I stripped the car of all electronics and installed a Tekin R8 speed control, LRP X12 3.5 with homemade internal fan, Spectrum micro receiver and pds 2413 ICS. This servo is half height and lets the Tekin have cooling room front and back. Why the R8. It is hot in Houston. Lots of 105F days this Summer. This Tekin has not thermalled in my wide pan or Touring car ever with the hottest motors geared to best performance rather than, I will be lucky if it just just makes 6 minutes. It comes off the track at 110F usually.

Balance Side to Side
With a normal size speed control the Losi balanced up side to side with few mods. With this Tekin I had to add 1.5 ounces of lead strips to the right side rail. The car is already overweight a couple ounces so I decided a mod was necessary. I used two .875 inch red hex CRC posts (center posts) on each end of the battery very near the outside rail for my battery strap. I used a graphite battery strap from the TC4 with holes drilled for 2s LiPo length packs. I partially cut the edge of the car. I attached the strap and battery so it could slide left and right. I put it on the scales like in the first photo and set the side to side weights exactly equal with no lead.

Next get corner weights equal. Typically the left rear corner is heavy on a touring car. The battery can be angled to compensate for this weight. I put the front wheels on the corner weight scales like in the second picture. The rear tires are on a beam the same height as the scales. I moved the front shock collars until the front wheels were even. I only needed a microscopic movement which was hard with the sliding collars. Now I reversed the car and angled the battery until the rears were even. I rechecked things. Then I installed a small adjustable CRC graphite fence inside of the battery that I will use with a tape strip to hold the battery just right. Worked great today. Track report to follow.

Pics
Setting side to side weight, two scales left tires on beam, right tires on beam
Setting corner weight. First front tires on scales back tires on beam. Set fronts equal. Now reverse car (shown) and move weight only front or back get back tires even.New battery hold down. Also see Manutech.com and Atomicmods.com for adjustable trays.


BEWARE the SINGLE BELT
Attached Thumbnails
LOSI XXX-S, Tips and Tricks, Open Mod, etc-losi-xxx-s-rtr-002.jpg   LOSI XXX-S, Tips and Tricks, Open Mod, etc-losi-xxx-s-rtr-001.jpg   LOSI XXX-S, Tips and Tricks, Open Mod, etc-losi-xxx-s-rtr-005.jpg   LOSI XXX-S, Tips and Tricks, Open Mod, etc-losi-xxx-s-battery-tray-001.jpg   LOSI XXX-S, Tips and Tricks, Open Mod, etc-losi-xxx-rtr-001.jpg  

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Last edited by Slo_E4; 02-22-2015 at 06:00 AM.
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Old 10-28-2009, 06:47 PM   #2
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Great stuff John....but help a brother out...what about us poor slobs who still run stock ( 17.5/Lipo RCGT to be exact). I'm a die hard believer in the xxxs (as my fellow racers laugh at me) but I'm sure I could learn alot from someone with REAL experience racing and modding it.
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Old 10-28-2009, 06:55 PM   #3
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Evoracer-No problem at all. That is what the etc. was for. All my stock tips as well as other guys will be available. I ran stock a long time with it. We might as well start with the belt. I am favoring this HD long belt for mod, but I don't think it is the ticket for stock. It is on the stiff side. Some of you guys doing well in stock racing please post the best belt and belt treatment. I think it should be adjusted relatively loose but no skipping on power.

Of course, weight balance is no less important for stock. The more the car accelerates straight the more power you are able to add on corner exit.
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Old 10-28-2009, 07:27 PM   #4
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baddest TC for mod IMO!!! great stuff!! ran it at the HUDY race in Ga round 2004 (i think). couldn't get my T1 FOC to work after hours of set-up. put the losi down and it was dailed right outa the trunk!!
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Old 10-28-2009, 08:03 PM   #5
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Here's one of the things I'm most curious about. The kingpins are mounted straight in to the pivots rather than having pivot balls and, especially in the front where the pin angle from front to back is fairly extreme, it would seem this would be a source of friction that prevents the suspension from working as well as it could. Another rctecher (dajohnwee) offers up the idea that using a 2degree rear pivot mount in the front is the way to go thus decreasing the front a-arm "rake". Any thoughts on this?? BTW, I currently use the black belt and find the action very smooth as compared to my ta05. Do you think the yellow or blue belt would actually be more friction free??
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Old 10-28-2009, 08:21 PM   #6
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Thanks for the post guys. Off to a good start.

nomaak-same here.

Kinkpins. These consist of the upper ballstud rotating in the little flanged steel bushing and the lower button head screw that rotates in the same type of steel bushing. No problem with these friction wise. These are universally used on lots of cars now. Durability wise I found it helped to put the smallest amount of blue loctite on the threads of the ball stud and the screw and then assemble it. Then the screw bushing and C-hub (caster block) solidify into a solid part. The bushing rotates in the C-hub plastic (no loctite must seep in there). Constant unscrewing and breakage is much reduced. You may need to heat the screw 20 seconds with a soldering iron to remove it (or until the first smoke). No harm is done by the loctite or the heat.

Now as far as removing the angle of the arm, the benefit is from removing rearward angle of the drive axles. Changing the arm angle does change this. I have seen several ways to do this. I made custom rear hinge pin mounts that moved the rear of the hinge pin out for stock. This is some trouble but not that hard. Some of the team drivers after this were sawing the nubs off the front hinge pin mount, drilling the hinge pin hole deeper and using longer inner hinge pins and spacers to move the arms forward. Using a narrow front mount would be equally effective if you get no bind on the drive axles. Again for mod don't mess with this, it is good stuff.

I will have to defer to you guys on belts. I think we had one belt (yellow)and it was soft. Maybe too soft for stock. Great for mod.

One vote for the black belt noted. That is what I am using outdoors. It seems too stiff for stock to me.
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Old 10-28-2009, 08:25 PM   #7
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oops, my bad...I called them king pins but was referring to the hings pins. No problem with the king pins. Sorry.

It would seem your fix would work best.Effectively widening the front rear pivot location and thus straightening the angle from front to back. The team fix seems like all it would do is change the driveshaft angle. Is the arm angle irrelavent or is there actually some benefit to the "sweep" of the arms ?

Correction...reread your original post about the chatter. So effectively....wouldnt the team fix be the better of the 2 choices ?

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Old 10-29-2009, 12:58 AM   #8
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great too see this car is still alive and kicking
And someone willing too help all of us others out

I currently run one of thes in stock class (17.5) and i find the only thing letting it down is the drver lol and my lack of set up knowledge lol
otherwise its a very forgiving car and easy 2 work on
and the sealed drive train reduces maintenece too lol
i came up with my owb belt combo for this car and so far it seems too work great dunno if there is a better solution but it works for me atm.
and it still seems fairly free and hasnt caused any probs no mattter ho tight or loose i run it.

Now what i wanna know is what the go with belt tension is it loose= top speed, and tight = acceleration??
or hav i got it wrong, seems too me that's how it works

and evo i tried that 2 degree rear block up front = sweet!!! so much smoother on high speed corners more planted less fidigity
now jus gotta get the rest set up an learn too drive better lol
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Old 10-29-2009, 06:22 AM   #9
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Quote:
Originally Posted by paraletic View Post
i came up with my owb belt combo for this car and so far it seems too work great dunno if there is a better solution but it works for me atm.
and it still seems fairly free and hasnt caused any probs no mattter ho tight or loose i run it.
So what belt combo are you running?? Looks like I'll have to try that 2degree block in the front.
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Old 10-29-2009, 06:28 AM   #10
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evoracer-Hinge-pin friction. I think there is less friction on the hinge pin if you sweep the A-arms back. There is no friction gain with my mod. The only gain is more forward traction from less drive axle angle.
The team mod would be better for mod as it keeps the swept back arms, it improves only drive axle angle, but also lengthens the car, but then I like the car as is for mod. I may try those two mods down the road though. I think I have a spare 2 degree rear pivot support. It might be helpfull on my long track to have a slightly longer car, though.

Paraletic-thanks for the post. You mention your secret belt setup. Spill the beans, you can tell us, we can keep a secret.

As high traction causes a tight belt and slows a stock motor, I suggest running a fairly loose belt in stock to start with. This will also help top speed by allowing the belt to float on a layer of air at higher speeds.

pic-My home track. Mikes-HobbyShop.com
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Old 10-29-2009, 07:43 AM   #11
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Great thread!

A simple question. I bought a used xxx-s RTR for VTA, great runner on carpet.
Recently I went to rebuild the diffs and found that instead of a spring there were 6 bevelled washers. The manual shows a spring. Was this a mod?, an improvised fix? or a production change? I can see that if I alternate the washers like this ()()() it will work. Bottom line: Does it matter?

Thanks in advance, no hijack intended.
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Old 10-29-2009, 08:49 AM   #12
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The Belleville (spring) washers were in the original diff. They were replaced with a spring at about the JRXS type R time. Either one works fine. Put the pointy end of each washer toward the nut. Stack the six washers (not like your diagram). Tighten until it locks (flattens the washers), loosen 1/4 turn or so. My kit had the Belleville washers as well.

note the diff is easily adjusted without any dissasembly. Put a thin allen in the left side slot of the outdrive. Turn the right side wheel until the allen falls into the screw slot. Now tighten the diff by holding the allen and turning that right hand wheel. If your front diff is locked check it before every race day. It will loosen as the diff rings squeeze the gear plastic over time. On a ball diff check it every once in a while. Several times when new.
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Old 10-29-2009, 09:16 AM   #13
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Hey John

Don't let Evoracer fool you!! We run at the same track and if his car was any better it'd drive itself!!!
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Old 10-29-2009, 09:21 AM   #14
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I hope my recent performance at the series race wasn't an indication of that...the car would have done better WITHOUT me !!! LOL
Hey PJ...here I am still in love with the xxx-s. Still thinking about the cyclone. That deal I had fell through but there's others. Then again....with John's help I may just end up with a killer XXX. I must admit....the support level available for xxxs owners on this forum and other places is just fantastic. X owners are never alone.
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Old 10-29-2009, 10:17 AM   #15
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John, in ref to your ESC is that the RS you're running? Couldnt find the R8 unless you're running that RX8 for 8th scale. Always been a tekin fan and obviously Florida has it's share of warm (otherwise known as "holy crap it's hot") days.

Right now I'm running all G+ cars...in your opinion for shorter, technical layout tracks would the Stiffzell AKA "stiff weasel" LOL chassis be a better choice?? And would you then be more inclined to use sway bars?? It seems the greater majority of G+ setups do not use them.
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