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 ½ 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 don’t 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
Last edited by Slo_E4; 02-22-2015 at 05:00 AM.