Tamiya Mini Cooper Rally Project

Page 1: Assembly

Here are a couple of pictures which were part of the eBay posting from which I purchased the model. I chose it primarily because the body and stickers looked to be in very good condition. The M-03 chassis on which it was mounted was sold to recover some of the money spent on the auction, and it turned out to have a pretty long list of upgrades which increased its value (though not its selling price). I kept the wheels and tires. The wheels are the right style for the Mini Rally, but they should really be chrome. I may replace them some day.

The M-05 Version II R never came as a complete model, it was only available as a chassis kit with no body, electronics, wheels, or tires. That makes the box pretty small, but the contents are not simple. In general M chassis are not very complex, but this one appears to have a lot more going on that most.

This picture shows the metal parts of Bag A of the kit that I was able to quickly find. All of the aluminum parts are black anodized rather than the standard Tamiya blue. We have an aluminum motor mount, servo mount, battery holders, lightweight hollow gear shafts, and full ball bearings.

The first step involves preparing the chassis halves. While most chassis either have a continuous tub, base plate, or are split along the length, this chassis is split in half side to side. The gearbox will be located between the sides. The aluminum motor mount is attached to one side. The aluminum battery holders stick out the sides to support a transverse mounted battery which apparently must be secured with "glass fiber tape", something I'd never heard of before. That's way too much hassle for me, so I reverted to the regular plastic battery mounts.

The kit comes with reinforced gears which I'm pretty such just means there is glass fiber in the plastic. The big gear holds the metal bevel gears for the differential. This is not a sealed diff, but it does use Tamiya's super thick Anti-Wear grease to give it a reasonable amount of resistance to slip.

These photos show how the gears fit between the chassis halves. This makes for a nicely protected gear mesh, but also means that it is very difficult to access the gears if any maintenance is required. The big gap in the back might look like it is for the battery, but actually the electronics will fit under those beams. The battery sits forward of that to move more weight over the front wheels.

Here are the metal parts for Bag B. Among them are some high strength, low friction king pins (step screws), some aluminum steering supports , some stainless hinge pins, and some very nice double cardan axles. These can support a much larger driven turning angle than dog bones or standard universals. They are fun to build as well.

Here the front suspension is being built and installed. It is very compact because of the short arms. The 1-piece lower arms are upgrades as are the uprights which are from the M-05 Ra, the rally version of the chassis. There is no camber adjustment, but the ride height can be changed by using an alternate set of holes on the uprights. This model is being built in the lowest configuration.

Now the dual bellcrank steering has been completed. I found it a bit strange that the little crank support brackets are aluminum but the cranks and bridge are plastic. Seems backwards. There are ball bearings in the cranks though, so the motion is quite nice.

The pinion gear mesh is not manually adjustable, instead there are 3 sets of holes to mount the motor which allow a 16, 18, or 20 tooth pinion gear. The kit comes with the 20 tooth gear which should provide the highest top speed. Because the motor is mounted inside the chassis, the weight is pretty well centered which makes for good lateral balance. The steering servo actually installs in the back. Although this model is capable of accepting a regular sized servo, it is really made to work best with a low profile servo so that's what I got.

The kit comes with very nice copper colored TRF (Tamiya Racing Factory) shocks. Of all the upgrades included in the "R" version of the chassis, these are the biggest deal. The bodies all full machined aluminum and the shafts are titanium coated. Piston heads and rod support rings are Delrin. The right hand picture shows how many parts it takes to make a single shock.

Now the shocks have been installed on the front and rear suspension. All 4 are built the same. They are very short and don't have much travel, but that's OK for a touring car chassis. Note that the rear upper links are adjustable to rear camber can be changed.

Going back a step, this picture shows the wheelbase adjustment of the M-05 chassis. While most M-chassis change the wheelbase with chassis plugs, this one is more subtle. There are multiple sets of holes on the rear of the chassis. Depending on which holes you use for the shock tower, on which side of the shock tower you install the upper links, which holes you use for the lower arm support, and which way around you install the support and arms, you can end up with a short (210mm), medium (225mm), or long (239mm) wheelbase. The entire rear axle moves to accommodate this variability which also means you need various rear body mounts to get the body to align with the axle position. I'm using the short wheelbase.

Now I can install the wheels, tires, and electronics. You can see the very long steering link which is needed since the steering servo is located all the way in the back. The ESC, servo, and receiver all sit side by side across the back.

Finally, the prepared body can be dropped onto the chassis. The body post locations made for a good alignment with the axles, but there was a bit of interference at the front and rear bumpers. I had to do a tiny bit of body trimming to make it fit perfectly.

Update 1:

After a while I decided that a standard silver can motor was not sufficiently special for a chassis of this excellence. On the other hand, I didn't really need the car to go any faster either. To balance these two requirements, I selected a 28T Lightly Tuned motor from Tamiya. This leaves the speed approximately the same but makes me feel better.

Update 2:

These pictures show my updated model after the rebuild. The servo and speed controller are different, and I also decided to use the aluminum battery mounts this time so I could use a lithium battery.

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