Mini 4WD Madness! Part 4: Drivetrain

The drivetrain is probably the most important part of a machine and there are uncountable ways to try and get the most speed out of it. The primary source of speed is of course the motor, and most users perform break ins to try and get peak performance out of it. With countless methods and no one true way, it becomes natural that break in methods are sort of a trade secret.

I am not an expert on choosing the right motor, so I will not go into too much detail. Besides, there is a lot of existing information on the internet. Nowadays, it is much easier to break in motors thanks to the appearance of smartphone apps that can measure the speed of a motor (examples: Giri, Try to measure RPM?, Mini4WD Lap Timer etc.), so you can gauge whether your methods are making a difference. According to Japanese bloggers, the type of brush can affect the effectiveness of a particular break in method, and in general the old generation of Tuned class motors and the Light Dash motor still retain metal brushes, while the faster motors use carbon brushes. Metal brushes conduct electricity better and gain more benefit from breaking in but have a shorter lifetime compared to carbon brushes.

Variables like break in voltage and duration also affect the outcome. Currently, I use 4 AA non-rechargeable batteries for 6V based on the results recorded on this Japanese page and break in as follows:

1. Forward for 1 minute
2. At least 3 minutes’ rest (motors that run hotter will take longer to cool down)
3. Reverse for 1 minute
4. At least 3 minutes’ rest
5. 5 sets for a total of 10 reps, taking at least 37 minutes total

Depending on luck of the draw as well, breaking in may provide a larger effect than usual. The most demanding users buy in bulk and pick the fastest motors, just like GPU binning.

Here I have briefly listed the results of this break in method on several motors, powered using a pair of rechargeable batteries.

	Atomic Tuned Pro	Hyper Dash Pro	Hyper Dash 3	Tamiya Handy Router motor
Before break in	15k	20k	20k	26k
After break in	16k	19k	19k	25k
After using electrical contact cleaner	18k	21k	21k	28k

The motors listed in the above table use carbon brushes as far as I can tell. The router motor appears to be a hidden gem, though it would probably be banned from official races. I also made a second attempt, using motors equipped with metal brushes.

	Torque Tuned 2	Torque Tuned 2 Pro	Light Dash	Light Dash Pro
Before break in	14.3k	13.8k	14.9k	15.1k
After break in	17.0k	16.6k	17.1k	17.1k
After using electrical contact cleaner	16.8k	17.2k	17.7k	18.0k

Since the measurement fluctuates I omitted some precision with the carbon brush-equipped motors as they had vastly different specs. With the metal brush-equipped motors, they were similar so I put in a bit more precision. As far as carbon brush-equipped motors are concerned, this method does not seem to provide any significant benefit. On the other hand, the metal brush-equipped motors see a noticeable boost.

I am also playing devil’s advocate and including the bottom row of data. Regulations forbid opening the motor to modify its internals, or using any sort of additive that leaks onto the tracks. This means that things like parts cleaner sprays straddle the line. If you wipe things down properly, I believe leaks can be prevented. While it doesn’t seem to have an effect on the metal brushes, the carbon brushes get a boost.

You can see that my Atomic Tuned Pro is on par with my Light Dash Pro in terms of performance. My Torque Tuned motors seem to be on the top end of their spec, while my Light Dash motors are on the bottom end, thus confirming the rumour that it is possible for an Atomic Tuned Pro to beat a Light Dash Pro.

Mini 4WD Madness! Part 3: Building a Body Mass Damper

It’s been some time since my last Mini 4WD-themed post. As of writing this Japan Cup 2016 is around the corner, but this time around you had to register by downloading some app and I missed the deadline. Besides, I don’t spend enough time tweaking my machines to have any confidence tackling the crazy Vertical Changer for one.

Anyway here in Japan, official races have been incorporating elements such as jumps and banks for the past few years, making the layouts of tracks more three-dimensional than before. As a result, speed isn’t the only important criteria, and poorly set-up machines no matter how fast would go off course and retire. To reduce the rebound after a landing, mass dampers are installed. Due to their weight, they have the disadvantage of slowing a machine down, but the increased stability they confer is incredibly vital.

While Tamiya has a wide range of mass dampers in various shapes and designs, some creative folks have come up with even more diverse, effective designs. Among the hardcore in Japan, they have somewhat nonsensical names which I won’t go into detail since they don’t seem to make sense. However the common characteristic among them is the increased actuation range compared to stock dampers which are usually weights sliding up and down a fixed pole or swing with small arcs.

One of the easiest designs is the hanging damper, where a pair of reinforcement plates mounted on either the front or rear reach across the length of the machine and has sliding weights mounted on the sides. Depending on the complexity of the design, you could either make the whole thing sit on top of the body, or cut the body so that it sits on top of the assembly instead, making it look more integrated with the machine as a whole.

Here I will show how I built my body mass damper which has the body attached on top so that it moves along with the damper. This design is for the AR Chassis where you will need 3 straight reinforcing plates, at least 2 X Chassis rear roller stays, a mass damper set with round weights, spacers and screws of assorted lengths. For convenience, you may also use a pair of throwaway pliers (ones you don’t mind damaging for cutting up the plates), diamond-tipped files and to speed things up, an electric router with a diamond cutting tool attachment.

Depending on its width, the chassis can get in the way of the straight plates. I believe that it would be even more difficult to build a damper for the wider MA chassis while the narrow Super II Chassis may require fewer parts. Hence, part of the plates will have to be cut depending on your layout and chassis.

In this case, I used carbon fibre plates which are stronger and lighter compared to FRP plates with the same design. Due to my incompetence/inexperience, the thinner sections on mine are weaker than they should as I damaged the surfaces with my cutting tool. The sections were removed to avoid the counter gear and motor areas of the chassis. Cuts were first made using an electric router, then filed smooth.

2 X Chassis rear stays were cut up as shown above. On the upper one, the left and right pieces are used while on the bottom, the centre piece is kept, and its edges filed smooth. The centre piece on the bottom is for keeping the straight plates parallel to each other and prevent the assembly from becoming lopsided like a parallelogram under lateral forces.

For added structural strength I cut up an FRP multi roller stay and mounted it at the rear like so. It turn out this part might not be needed after all.

You have a lot of freedom in building the damper. Here a straight plate was used to extend the sides, and two screws were used on each side to prevent the dampers from twisting to the sides. As the hanging damper experiences a lot of vibration, I used lock nuts throughout.

Since taking these pictures I tweaked the layout a bit to move the weights up front as close to the front wheels as possible, and swapped the lower extensions so that the weights don’t go past the line traced by the front and rear roller mounting positions to keep within official regulations.

Flat head screws were used on the side extensions, and recessed holes were made so that the underside is smooth. The lengths of the screws were chosen to get the weights as low as possible. A sponge was applied on the underside of the centre plate for cushioning. The protruding screw ends are for mounting the body on top.

The holes in the straight plates can be worn out over time where the damper is mounted to the chassis. To prevent this, brass eyelets can be glued to the holes. However, they are not sold and do not come with newer cars so I decided to improvise and cut up some aluminium pipes as a replacement.

Springs are used to keep the damper in position. Rubber tubing was used as a stopper for mounting the body to the damper.

As there is no hard and fast rule to the design, there are many variations and I am unsure which one is the most effective. As far as I can tell, in 2016 there is a trend of mounting the damper in front instead.

Mini 4WD Madness! Part 2: AR Chassis Bumperless Conversion

Edit: This post was written some time ago and after some more research I’ve decided to overhaul this post.

The advantages of a bumperless setup are:

• Possible weight savings and lower centre of gravity
• Increased setup possibilities such as lower front rollers
• Reduced distance between front and rear rollers
• Improved adaptability with bodies that otherwise would get in the way if you wanted to install a sliding damper for instance.

However, it also has the following demerits:

• Considerable effort required
• Front rollers will have upper thrust without further work
• Possible reduction in strength especially if using FRP plates
• Increased maintenance demands to maintain the thrust angle of the front rollers

You’ll have to cut up the front of your chassis to leave behind just two mounting holes.

The front base plate will be mounted to the chassis at the two remaining screw holes.

As the underside is tapered upwards, the base plate will have an upper thrust. Without further modification, there is an increased risk of the machine going off course.

To fix this, you can either use adjuster plates or cut up some unused polycarbonate from a clear body set to wedge in between the base plate and the roller mounting plate.

Result.

The original post will be left below.

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.

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.