1/10 Scale Electric Rally/Touring Car:

Yokomo YR-4 II Compact - Radio Controlled Model

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History and Info:

Introduced by Team Yokomo circa 1998, the 4WD YR4-2 Compact Touring Car, came with a number of bodyshell options, including BMW Z3 and Mercedes SLK.

The model was based on a short wheelbase version of the MR4-2 and is belt driven, on a double deck chassis, with ball differentials, coil spring over oil filled dampers, universal joint drive-shafts and sintered bronze bushings, ring type bearings.

Yokomo YR-4 II Compact - 1:10 Electric Touring Car

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To race the Yokomo YR-4 II Compact, it must be fine tuned to improve handling, provide responsive steering and give you the grip to cruise around corners at high speed, without slipping off the track. Small adjustments can make a Big difference and our step by step procedure, will guide you to the best Set-up for your individual driving style.

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Radio Controlled Model Accessories:

★ Yokomo YR4-2 Compact ★

★ Yokomo YR4-2 Compact Chassis ★

Buying a Used Yokomo YR-4 II
Touring Car (and What to look for)

There are essentially three reasons you might want to buy a used Yokomo YR-4 II Electric Touring Car; you may be a collector, looking to restore and display it; restore and sell for a profit; or simply restore and race an iconic vintage model. Personally, I used to get a buzz out of restoring an old clapped-out model, installing modern day electrics and maybe a few hop-ups, then showing the gang at our local club, just how competitive those old models could still be.

Cheap, pre-loved bargain models, parts and spares are always coming up for sale, but once you have made your purchase, 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 Touring Car you may discover, can easily be fixed.

Make a General Visual Inspection

Dampers
When you receive your used Yokomo 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 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.

Check the Body-Shell

If the body shell of your Yokomo YR-4 II 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 YR-4 II model, fit an under guard to stop dirt and gravel entering the chassis.

Drive Shafts and Turnbuckles

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 YR-4 II Touring Car model at a competitive level, I would also recommend you obtain and fit titanium pivot shafts, turnbuckles, tie rods and steering rods.

Examine the Drive System

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.

Pinions and 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.

Don't Neglect the Ball-Joints

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.

Steering Servo and Servo-Saver

Servo Gears
The YR-4 II 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.

Stabilizers

If body roll on your Yokomo YR-4 II 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.

Don't Forget those Bearings

If your used Yokomo 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 YR-4 II model and good racing.

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Manufacturers and Brands Catalogued, Listed and Reviewed 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 Models and 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.

RC Information and Advice:

★ Yokomo YR-4 II Compact ★

Hints, Tips and Information

Rechargeable Batteries
for RC Models

   At the time this article was written, there are four types of Rechargeable Batteries that are commonly in use for Radio Controlled Models.
Ni-Cad (Nickel Cadmium) Batteries have been around the longest. My first stick battery, purchased way back in 1987 was rated at 1200Mah (Mili Amp Hours) and with a silver can 27 Turn motor my Tamiya Boomerang would run around in the back yard for a good seven minutes before slowly coming to a stop. Ni-Cad development continued until around 1998 to a maximum rating of around 2000Mah and matchers pack builders and battery technicians were able to put together six cell packs with voltages approaching 7.4 Volts, to give those that could afford them, an edge over the rest.

   Ni-Mh (Nickel Metal Hydride) Batteries came along in the late 1990s, and by the year 2000 were available at ratings up to 3000Mah. Again, matchers and pack builders worked hard to provide the ardent racer with packs to provide that little bit of extra power, and ESC manufacturers also chipped in with improved controllers to take full advantage of this new technology.

   Now the problem wasn't gearing the car to get to the end of the race using the available battery power, but to find the brushed motor that could handle gear setting that provided the speed and acceleration without the motor overheating and wearing the commutator too much so it needed a skim after every 2 runs. My favourite at that time was the 9 Double.

   More recently, Li-Po (Lithium-Polymer) Batteries have appeared on the scene, providing are a huge step forward in performance when compared with Ni-Cad and Ni-Mh batteries.

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Hints, Tips and Information

Electric Motors for RC Models

Winds and Turns

Q/  What does 15x2 or 17x3 mean?
A/  The first number relates to the number of times the wires are wound round each of the 3 armature segments, the second number relates to the number of wires side by side. So a 15x2 would have 2 wires laid side by side and wrapped around each segment 15 times.

Q/  What is the difference in performance between a Low Turn motor (eg 11x1) and a High Turn motor (eg 27x1)?
A/  A Motor with Less Turns like an 11x1 means high current draw from the batteries which corresponds to less runtime, but More Power (Torque or Punch) Best for tracks with lots of corners and short straights where fast acceleration is needed. (use a small pinion)
Motors with More Turns like a 27x1 give you More runtime, but Less Power. So you get a smoother response and are therefore easier to drive. Better for less experienced drivers and Long straight, sweeping corner tracks. (with a large pinion). This is correct for Brushed, Modified and Stock Motors as well as Brushless Motors.

Q/  How do the number of winds effect a motor?