RCScrapyard ► Iconic Vintage Radio Controlled (RC) Model Car Archive ► Xpress MRR2 Junior. (Mini Road Runner II)
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1/10 Scale Electric Rally/Touring Car:

Xpress MRR2 Junior (Radio Controlled Model Review)


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History, Info (and How To Set-up Tips) for the Xpress MRR2 Junior:


  Introduced by Xpress circa 2007, the Xpress Mini Road Runner Junior Touring Car chassis - # MRR2-Junior - was an entry level model.

  The model is belt driven, on a double deck chassis, with ball differentials, coil spring over oil filled dampers, universal joint drive-shafts, sway-bars and ball bearings.

Xpress MRR2 Junior
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  To race the Xpress MRR2 Junior, it calls for fine tuning to attain better steering response and improve grip when cornering so you don't slide off the side of the track. Minute changes can make huge advancements. Our easy to understand list will show you how and lead you to the optimum Set-up to put you in front of the rest on the track.

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★ Xpress MRR2-Junior ★
Xpress MRR2-Junior

★ Xpress MRR2-Junior Chassis ★
Xpress MRR2-Junior Chassis

★ Xpress MRR2-Junior Chassis ★
Xpress MRR2-Junior Chassis

★ Xpress MRR2-Junior Chassis ★
Xpress MRR2-Junior Chassis


Buying a Used Xpress MRR2
Touring Car (and What to look for)


   Buying a used Xpress MRR2 Electric Touring Car, or any used RC Model, has a number of advantages. It is generally cheaper than new, ready built and may come with a variety of expensive hop-ups already installed. Cheap, pre-loved bargains are always becoming available. However, depending on the age of your purchase, it may need a little tender loving care before you can take it out on the road.

   The one thing you will always need is an instruction manual. If not supplied with your purchase, they can often be downloaded from the Xpress website, or purchased separately on eBay. With an instruction manual, any problems with your model Touring Car you may discover can easily be fixed.

Dampers
   When you receive your used Xpress Touring Car, make a general visual inspection of the chassis, front and rear wishbones, suspension shock towers etc, for any broken parts that may need to be replaced. Then, take a screwdriver and box spanner and check each self tapping screw and nut for security, taking care not to over tighten.

   Next, for those Xpress models with oil filled shock absorbers, remove them from the chassis and dismantle the coil springs. The damper shafts should push in and pull out with a smooth action. If you feel a jolt as you change direction, this means the oil has leaked out and must be topped up. At the same time, change the O-Ring seals to prevent more leakage. Also check the damper shafts for damage. If they are scratched, change them as soon as possible.

   If the body shell of your Xpress MRR2 is broken, ripped or damaged in any way, this can be easily repaired with rubber solution glue. Also, for added protection and if available for your MRR2 model, fit an under guard to stop dirt and gravel entering the chassis.

Titanium Turnbuckles
   Examine the drive shafts for wear and replace as required. If possible, change them for titanium. The steel shafts wear and bend too easily.

   If you intend to race your MRR2 Touring Car model at a competitive level, I would also recommend you obtain and fit titanium pivot shafts, turnbuckles, tie rods and steering rods.

   Drive Belts need checking at regular intervals for wear, tension and damage. If deemed necessary, adjust the tensioning pulley until the belt can be depressed in the centre by no more than around 5mm. If the belt was slack, also examine the drive pulleys for wear. The teeth should provide a well seated fit for the belt teeth and not be rounded on the corners. If the belt teeth do not fit snugly, change the pulleys as soon as possible. For top level racing it may be prudent to replace all belts and pulleys after each race meeting.

Spur Gears
   Gears are a weakness on all Touring Car RC models. Head on collisions can easily damage the gear teeth on nylon and plastic spur gears. Heavy impacts can also loosen the nuts or self tapping screws that hold the Electric Motor in Position, allowing the pinion gear to pull out of mesh slightly and rip the tops off the teeth on your spur gear. To minimise this possibility, fit bolts with locking nuts to the Electric Motor mount and remember to check them for security after every two or three runs.

   Ball joints always cause problems. For top level Electric Touring Car racing, the plastic ball connectors should be checked and if deemed necessary changed after every meeting. A simple thing like a loose fitting connector popping off could easily end your race, so better safe than sorry.

Servo Gears
   The MRR2 steering servo is also prone to damage. In high speed crash situations, the fragile gear teeth of the servo can be broken off, rendering your expensive servo useless, so be sure to obtain a good quality "Servo Saver". Check out my Servo Information article.

   If body roll on your Xpress MRR2 is a problem, handling can be improved with the use of stabilizers, anti roll or sway bars, stiffer tuning springs and, or, thicker silicone oil in the dampers.

Ball Bearings
   If your used Xpress Touring Car comes with plastic and sintered brass bushings (ring type bearings), check the shafts that run in them for wear. Dust and grit can get into these bearings and abrade the shafts. Therefore, you should replace them all with shielded ball bearings. If the model has been run with ring type bearings, you may have to change all the axles and driveshafts. For more information, take a look at my article, How to get the best from your Bearings.

   Finally, good luck with your MRR2 model and good racing.




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Or, check out our RC Model Car Setup Guide


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Manufacturers and Brands Catalogued and Listed by RC-Scrapyard.


   At present, the RC Model Manufacturers, Brands and Distributors covered by us are: ABC Hobby, Academy, Acme Racing, Agama Racing, Amewi, Ansmann Racing, ARRMA, Team Associated, Atomic RC, Axial, AYK, Bolink, BSD Racing, Capricorn, Carisma, Carson, Caster Racing, Cen, Corally, Custom Works, Durango, Duratrax, ECX - Electrix, Exceed RC, FG Modellsport, FS-Racing, FTX, Fujimi, Gmade, GS-Racing, Harm, HBX, Helion, Heng Long, Himoto Racing, Hirobo, Hitari, Hobao, Hong-Nor, Hot Bodies, HPI, HSP, Intech, Integy, Jamara, JQ Products, Kawada, Kyosho, Losi, LRP, Maisto, Mardave, Marui, Maverick, MCD Racing, Megatech, Mugen, New Bright, Nichimo, Nikko, Nkok, Ofna, Pro-Pulse, Protech, PTI, RC4WD, Redcat Racing, RJ-Speed, Robitronic, Schumacher, Seben, Serpent, Smartech, Sportwerks, Step-Up, Tamiya, Team-C Racing, Team Magic, Thunder Tiger, Tomy, Top Racing, Traxxas, Trinity, Tyco, Vaterra RC, Venom, VRX Racing, WLToys, X-Factory, Xmods, Xpress, Xray, XTM, Yankee RC, Yokomo, ZD Racing and Zipzaps.

   This is an ongoing project, with new and "lost in time" RC Model Brands being added as they are found and although most of those listed above have been covered in relative detail, some are still being researched and will be completed in the near future.


















Hints and Tips

Roll Center

   One of the least understood settings on RC model cars is concept of roll center. The simple definition of roll center is a point in space that the chassis rolls from side to side as the car maneuvers around a corner.

   To calculate roll center you have to consider things like the height of the axles, the inside and outside camber link positioning, the length of the suspension arms and the location of their inside pivot point. Sounds complicated doesn't it and in truth it is.

   On all RC model cars, most of the cars weight is above the chassis and the center of gravity of the car is not only from front to rear, but also from top to bottom. This point is called the "true" center of gravity and is the point around which the weight of the car will want to roll from side to side, but it is the roll center of the chassis that the chassis will actually roll around, not the center of gravity.

   Once you have determined the positions of roll center and center of gravity, you can calculate the "roll moment". It is this that determines how easily the chassis will roll from side to side.

   But what does all this mean? I hear you ask. Well, it gives you some insight to what changing the position of your camber links can do to the way your car handles.

   Lowering the outside camber links, lowers the roll center, so conversely, raising the outside link position raises the roll center.

   Lowering the inside camber link position raises roll center and raising the inside camber link position, lowers the roll center.

   Any of these adjustments will affect the "roll moment" and therefore you have some control of body roll.

   The length of the camber link bars affects the speed of roll center change as the car driver around corners. Longer links increase the rate of change. Shorter links decreases the rate of change.

   Adjustments to the roll center will change the way the car reacts in a number of ways.

   Lowering the front roll center gives more steering under acceleration, but the car is less responsive. Ideal for smooth high grip tracks, with long sweeping corners.

   Raising the front roll center provides less steering when accelerating out of the corner, but the car feels more responsive and is less prone to traction roll. Best for high grip twisty tracks.

   Lower rear roll center improves grip under acceleration, but reduced grip when breaking. Helpful to avoid traction roll as you enter the corner and tracks with low grip to increase traction.

   Higher rear roll center gives you less under acceleration, but the car is more responsive. Works for high grip twisty tracks to reduce traction roll.

For More Setup Information check out my Hints and Tips page.







Hints and Tips

Battery Connectors

   Over the years I have been racing radio controlled model cars of all descriptions, I have tried a number of different connectors for my batteries.

   My first car was a Tamiya Boomerang and of course the batteries I used all had the standard Tamiya connectors, which were fine with the kit supplied 27T silver can electric motor, but I soon discovered their problem when I installed my first Modified motor. The high current demands of the motor created so much heat, the plastic surround of the connectors melted and fused together. No matter how I tried they could not be disconnected. My only option was to cut the wires.

   From there I moved over to Corally connectors, commonly referred to by many now as Bullet connectors. Comprising of a short length of 4mm gold plated tube at one end and what looks like what we used to call a Chinese lantern fitting that slotted inside the tube, also gold plated. Although they were highly efficient and reasonably easy to install and use, I never really took to this type of connector, I think it was the fact that there was always the possibility of the positive and negative being connected wrongly in poor light and also that if positioned side by side, each connector could work loose and become exposed, leaving the possibility of a short circuit.

   Then I remember buying some second hand batteries at an area meeting one day, they had these little red block connectors I soon learned were "Deans" rated at around 40 Amps. They looked like just what I was looking for so I gave them a try. They worked fine, although I didn't like the shortness of the part to be soldered. However, for about two years they were my connector of choice, until I stumbled across an advert in the "Radio Race Car International" magazine.

   The latest development in connectors at that time were named "Power Pole", made by a company called Anderson and were rated at 45 Amps. The design uses a small tube, plated with silver, with a short extending lip, that slots over the exposed wire and can either be crimped onto the wire or soldered. For safety and efficiency, I prefer the latter. To complete the connector, a colour coded plastic cover fits neatly over it.

   It was way back in 1995 I first used Power-Pole and to this day they are still the most efficient I have come across and never overheat.

   So, if you are looking for a connector to change over to, that has a high current rating and won't cause you any overheating problems "Anderson Power Pole" is the one I recommend.

For More Setup Information check out my Hints and Tips page.










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