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1/10 Scale Electric Rally/Touring Car:

Yokomo MR4 Rally (Radio Controlled Model Review)


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History, Info (and How To Set-up Tips) for the Yokomo MR4 Rally:


  Introduced by Team Yokomo circa 1999, the 4WD MR4 Rally, was basically an MR4-TC with rally tires and a protective sealing under bodyshell.

  A number of kits were available: Basic kits MR4IW - Subaru Impreza WRC, MR4CW - Toyota Corolla WRC and MR4FW - Ford Focus WRC: Kits with 10 lay-shaft and axle Ball Bearings, MR4IWB / MR4CWB / and MR4FWB: And also Deal Kits with full ball bearings, motor and ESC, MR4IWD / MR4CWD / and MR4FWD.

  All Rally model kits were belt driven, on a molded plastic chassis, with ball differentials, coil spring over oil filled dampers, dogbone drive-shafts and bushings or ball bearings, depending on the kit.

Yokomo MR4 Rally - 1:10 Electric WRC Car
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  To race the Yokomo MR4 Rally, you need to tweak and adjust all you can to give your car improved handling, stability and grip to ease around the curves and keep you on the track. One little setting change can transform your car into a world beater. Just follow our chart to attain the most favourable Set-up to suit your particular needs on any track.

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★ Yokomo MR4-Rally ★
Yokomo MR4-Rally

★ Yokomo MR4-Rally Chassis ★
Yokomo MR4-Rally Chassis

★ Yokomo MR4-Rally Under-Body ★
Yokomo MR4-Rally Under-Body

★ Yokomo MR4-Rally ★
Yokomo MR4-Rally


Buying a Used Yokomo MR4
Rally Car (and What to look for)


   Buying a used Yokomo MR4 Electric Rally 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 Yokomo website, or purchased separately on eBay. With an instruction manual, any problems with your model Rally Car you may discover can easily be fixed.

Dampers
   When you receive your used Yokomo Rally 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 Yokomo 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 Yokomo MR4 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 MR4 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 MR4 Rally 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 Rally 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 Rally 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 MR4 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 Yokomo MR4 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 Yokomo Rally 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 MR4 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.





















Yokomo MR4 Rally Chassis
Yokomo MR4 Rally - Chassis


Hints and Tips

Soldering

   In the sport of Radio Controlled racing, there are a number of things you have to learn to get you up there with the best. One of the most difficult, for those with little practical skill, is the art of Soldering.

   For their 540 silver can motors, Tamiya provide two wires, typically green and yellow, soldered to the endbell, with two bullet connectors to plug into the speed controller. While this is fine for bashing around the back yard, as you advance to a higher level you will soon find just how inefficient this method is.

   Motor wires are best soldered directly to the ESC. That way no energy is lost through high current draw. Some of the top drivers at one time even used to solder their batteries directly to the ESC, but these days with connectors such as "Deans" and "Power Pole" this isn't necessary but I still wouldn't use any kind of connector for the motor.

   There are basically two kinds of solder. Plumbers solder which is made up of 60% Lead and 40% Tin, where as electrical solder is the opposite 40% Lead with 60% Tin. NEVER use plumbers solder for your battery, ESC or motor joints. Lead melts at 327 degrees C, where as tin melts at 232 degrees C. The higher Lead content of plumbers means it melts at a higher temperature, which is not good for your battery cells. Also, Tin has almost half the electrical resistance of lead, so with the higher Tin content of electrical solder, electricity flows much easier to your motor.

   More recently, due to the European regulations for lead use, lead free solders are becoming more widely used well, in Europe anyway. The problem with lead free is the melting temperature it is much higher, making it difficult to produce reliable joints.

   Lead, as we know, is a poison to the body if ingested or inhaled in certain quantities. so when using lead based solder, try not to inhale any of the fumes and always wash your hands after completing your work. One of my friends also wears cotton gloves, but I find these cumbersome.

   For me lead / tin solder is far easier to use and if used with care, has less potential to damage your batteries having a much lower melting temperature.

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







Hints and Tips

Tire Inserts

   Once upon a time, all RC model tires were equal they were all trash. None of the old tires had any kind of internal support, because the hard compound they were made of didn't need it. But that was before the newer soft compounds were developed. These new tires were so soft that if some kind of insert was not used they would just lay flat under the weight of the car. Thus, the new science of tire inserts was born.

   The basic soft foam inserts that come with many off-road rubber tires can be in one of two types. They can be basic rings of sponge, or the cheap and nasty strips of sponge. Both will often need some work done to them before they are inserted into the tires.

   Most of the top off-road drivers will carefully trim the edges of each sponge where they make contact with the inside of the tires. The idea is to reduce the effect of any hard edge when the tire hits the ground. If this is beneficial is debatable, but those I talked to said it does improve grip when cornering.

   On-road cars on the other hand have the luxury of only having to make the choice between hard, medium and soft, molded sponge or rubber inserts that fit snugly inside the wheels and I can testify, the effect of these inserts can make a big difference on the track.

   When you get to the race track, the first thing you check is the track temperature. This gives you an insight into which tire to try first. In my hay day, I would use three compounds, soft medium and hard, each prepared, glued to the wheels with soft, medium and hard inserts, so a total of nine sets of wheels with tires and inserts. Depending on the track temperature, my first practice session would be with the medium insert, then depending on the grip I got from those, I would either stick with them or for more grip try the softer insert. If the car had too much grip and a tendency to over-steer I would move on to the harder insert. Once the right tire and insert combination is found, only then I would try other settings to improve the cars handling. Remember, one change at a time.

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










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