Mini 4WD Madness! Part 1: Getting Started

This is a new series of posts about building and setting up a Tamiya Mini 4WD machine from scratch. I’ll be sharing my machine and setup as well has how it was built. While this machine is not battle-proven in official races, the current setup has an average speed and I’m still working on improvements to its stability.

I decided to build a machine recently but due to official race regulations requiring a painted body, I couldn’t make it to enter the Spring 2016 Japan Cup qualification which was held at Kumamoto Prefecture, near where I live.

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The last time I played with these things was probably around 18 to 20 years ago, where as a kid the bottleneck was pocket money and the parts on your machine were limited to whatever you could afford back then with your meagre savings. Apparently in Japan Mini 4WD is experiencing a sort of revival recently, and there are numerous changes and new parts introduced over the years. Of note this time round is the heavy emphasis on jump/airborne stability as race courses are three-dimensional with jumps where poorly set-up machines will fly off course.

Tamiya introduced the Mini 4WD Pro series which uses a double shaft motor midship layout a few years ago. While the old, venerable VS Chassis is still highly competitive, I decided to pick the Aero Avante with the AR Chassis, a relatively new design that retains the shaft-driven 4WD setup. The Aero Avante also made an appearance as a life-size car.

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This pic from Tamiya’s website shows the AR Chassis details. The English site is a horrendous outdated mess by the way. This chassis is unique with an included rear skid bar and an aerodynamic design. However this is also the heaviest shaft-driven 4WD chassis to date. Tamiya has also released the Super-II Chassis which is an update of the Super 1 Chassis, while the double shafted MS Chassis is updated to the MA Chassis with a monocoque design and aerodynamics adapted from the AR Chassis. In retrospect, the Super-II and MA Chassis might be more competitive than the AR Chassis.

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Here’s a pic of the Aero Avante assembled straight out of the box. The chassis has a built-in rear stay, preinstalled rear skid bar and 6 rollers. I will be focusing on setting up the AR Chassis in the next few posts, and in this one I will be showing off the tools I used.

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To make it easier to modify the machine and parts, I bought a battery-operated router. You can of course use any other one, but out of convenience I got this from a model shop near where I live. Having to pay the full retail price with tax at a mom and pop store, it hit me at that time why small businesses like these were closing down because they simply can’t compete against huge companies like Amazon with their generous discounts.

I also went to a Daiso store to buy a cheap diamond-tipped cutting wheel and mandrel set to use with this router, some diamond-tipped files as well as a cheap large pair of pliers for cutting up FRP/carbon plates. Never use model nippers as the blades will be ruined.

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Here are pictures of some of the parts I bought. I’ve also listed them below. Due to poor planning some extras were left over, such as the fluorine coated gear shafts.

Drivetrain

Choice of motor is up to the individual, and a lot of guides advise you to use a -Tuned motor instead of jumping straight to the -Dash motors without a proper set-up. As the AR Chassis is punishing on the drivetrain, you have to use carbon-reinforced gears for the pinion and crown gears.

  • Super X Chassis gold plated terminal set
  • 60mm hollow stainless steel shaft. This turned out to be a mistake on my part as they are very weak and cannot withstand much punishment.
  • 60mm/72mm black reinforced shafts
  • AO-1011 620 ball bearings. This set comes as a pair so you need at least two pairs. I bought a lot more extra due to poor planning.
  • Carbon reinforced 8T pinion gears
  • Setting gear set for AR Chassis. This set also comes with one fluorine-coated counter gear shaft and one 620 bearing.
  • Large diameter carbon reinforced wheel set
  • Large diameter extra low-profile tyres. I used third party ones so I didn’t have to make my own extra low-profile tyres. Once they are sufficiently worn I’m sure you can’t tell the difference between them and original Tamiya tyres that are trimmed.

Rollers

Official regulations limit rollers to six. I’m using the largest 19mm ones, with one pair in front and two pairs at the back.

  • HG lightweight 19mm aluminum ball-race rollers (ringless)
  • 19mm aluminum rollers w/ plastic rings (dish type)
  • Large diameter stabilizer head set (17mm)
  • 2mm cap screw set. While these are slightly pricey, they are apparently stronger than normal screws, and I used two sets for the roller posts since one set only comes with one pair of 30mm screws. Alternatively, some people use motor shafts as roller posts.

Bumpers

For this machine I decided to go with a bumperless setup and replace the chassis bumpers with FRP/carbon stays. While carbon plates are have a higher strength-to-weight ratio, they are expensive and are limited edition so you may have to settle for FRP equivalents in most cases. If you decide not to go this route, you can simply get the AR Chassis basic tune-up parts set which comes with FRP front and rear stays to reinforce the stock chassis.

  • FRP multi rear roller setting stay. For my setup, I used three sets. This is an incredibly useful and versatile part due to the abundant mounting holes. On Amazon these are often sold by other merchants at marked up prices.
  • HG carbon reinforcing plate (1.5mm). The FRP reinforcing plates are also useful and at this point in time the carbon versions are still around so I used them as much as possible. Each set comes with two plates and for the bumpers, I used three plates. They are pricey but slightly cheaper to get from Amazon.
  • Brake sponge set
  • Various lengths of flat head screws. These are sold by a third party and I use these on the bottom of the bumpers to ensure the bottom surface is smooth. If you can’t get these, you can still make do with the normal screws as well.
  • Aluminum spacer set. These are essential parts and I bought two sets so far.
  • 2mm lock nuts. Normal nuts tend to loosen with vibration, so I used lock nuts instead. These are pricey but worth it in my opinion. So far I have bought three sets.

Mass dampers

With the emphasis on jump stability, mass dampers are now an essential part of a setup and can make or break a competent machine. Here I will be making a body mass damper, something that is probably considered a basic setup here.

  • Mass damper block set (6x6x32mm). There is the slightly heavier 8x8x32mm version on my setup they may exceed size regulations so I’m using the smaller version.
  • Mass damper set w/ ball connectors (block weight). While you can simply get two of the previous set, I got this one instead to diversify my parts.
  • HG carbon reinforcing plate (1.5mm). For my body damper setup I used three plates.
  • FRP rear roller stay for Super X Chassis. This is used for the body damper. You need at least two sets.
  • FRP multi roller setting stay. Also used for the body damper. You can skip this for a third Super X Chassis stay instead.
  • Mass damper set (heavy). This is the weight used for the body damper. You can use other weights as well.
  • AO-1034 Sliding damper spring set. This is used to keep the body damper in position and prevent it from sliding up and down its pole freely.

In the next posts I will show how I converted the AR Chassis to a bumperless setup, and how I built the body damper.

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