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Tamiya RM01X Build and Review - Part 2

Hopefully, this will give an insight in to the basics for setting the car up and getting it running. Fine tuning is left to individual...


Hopefully, this will give an insight in to the basics for setting the car up and getting it running. Fine tuning is left to individual preference, but this should give a neutral car as a base setting and avoid any 'build errors' that may result in a bad handling car.

Making the car legal
There are a number of construction rules the car should meet for UK competition. The few to be aware of are as follows:

  • Roll Mast - "1.17 Roll-over masts/antennas must be fitted, and must have a safe blunt end. The minimum height of the rollover mast is 150 mm from the track surface. Rollover masts/antenna will be made from fibre-glass or carbon-fibre only, with a minimum outside diameter of 2.9 mm and a maximum outside diameter of 3.4 m/m." The car does not come with a rigid roll mast. Some clubs specify this and BRCA National rules call for one.  Masts are readily available and just push fit in to the antennae mount on the car.
  • Max Width - "1.10 Overall maximum width of the rolling chassis to be 172mm." The only are the car will fail on is the width of the rear axle. Use the TA54367 Rear Tread Spacer Set to adjust the axle width. Different manufacturers wheels have different offsets, so require different shimming. For Jaco/Mobgum/Contact wheels I have used the 1mm spacer each side to bring the car to 171.8mm.
  • Min Weight - "1.2 Minimum weight is 730 grams." The car when first built weighed 732 grams with the body. I have now fitted a decent pack of cells and it has jumped to 751 grams. One to keep an eye on.
  • Min Ride Height - "1.24 The recommended minimum ground clearance of the car, not including the spur gear, is 3mm; this will be checked after each qualifying heat and final race." Ideally you wont go below this height anyway, as the car will rub on the carpet which will adversely affect the handling. Aim for 3.5mm to 4mm in most cases. I will cover this later.
Extracts are from the current BRCA LMP12 rules.

Basic Settings

When making changes, ensure the car is race ready (minus bodyshell), with the cells fitted. This will ensure you are setting the car up at race weight.

Tyres

These are a matter of personal choice and depend on what motor you will be using. I run a 13.5 in blinky mode at my local club so opted for Yellow rears and Magenta fronts for my first outing. When selecting the tyres, try to match them up so the fronts are 2mm smaller diameter than the rears.

Front Suspension
I'm generally lazy with my cars. I get the front end to work, then never touch it again except for maintenance. The kit front end is similar to my Speedmerchant, with limited adjustment, so it suits me. 

  • Castor - I have yet to measure the castor, but it looks to be between 2 and 4 degrees. I run 2 degrees on the Speedmerchant, so I have not made any adjustment prior to the first run. Generally, less castor makes the car turn in sharper. There are more detailed articles on this than here though.
  • Camber - camber change is only used (except in extreme cases) so that the front tyres wear evenly. If you see coning on the front tyres, you need to adjust it. I've found 1.5 degrees perfect on the Speedmerchant. The Tamiya has 1 degree as standard, which I feel will wear out the outer part of the tyre quicker than the inner. There are no turnbuckles or any fancy way of adjusting the camber. The only way is a very effective 'bodge'. I use the foil pack that spare scalpel blades come in and cut a couple of small strips for each side. Loosen the 4mm screws that hold the uprights to the chassis and shove the foil in until it touches the screw. Then bolt it up. Adding foil to the outside of the upright increases negative camber. Inside the upright decrease camber. Simples. I have used a double foil thickness on the outside to give me the desired 1.5 degrees. See picture below.

  • Ride height - the kit comes complete with a set of 0.5mm and 1mm shims that slot between the suspension arm and chassis to adjust ride height. Simple as that. You will need a ride height gauge and a flat surface to work on. Even though this relates to a 12L4, the basic principle can be seen here: http://www.carsrcracing.co.uk/?page_id=62
Measuring front ride height

  • Steering - set the servo so the output spline is as close to the centreline of the car as possible. Then trim the servo saver so it is vertical. Do not adjust it (except if required on the track). This will give you equal steering lock each side. Any minor corrections can be taken up with the EPA on the transmitter. Fit the turnbuckles. Looking down from the top of the car they should be at 90 degrees from the centreline. Shims are included to move the servo forward if required. This should give you the ideal amount of Ackermann (inside wheel turning more than the outside). I used a Futaba 9650 servo and found the servo posts are drilled to take a standard servo. If I hadn't cut them off already, the servo comes with lugs to bolt straight to the chassis, so no posts required. If you do use the posts, just use one bolt each side, or if like me you have lots of bits lying around us Associated ones. Now shim the balljoint on the steering arm so the turnbuckles are just below horizontal to the floor. With the suspension compressed, they should go horizontal but no further. Set like this, as the suspension compresses the turnbuckle raises and in effect gets longer, providing a little toe in for stability. If they then go above horizontal, they will go to toe out and upset the car.
  • Springs - the kit comes with a complete range of front springs. I am starting out with the 2nd softest. On most 1/12th cars, when built the spring is relaxed with the suspension off load. To add a little preload we add a shim. The Tamiya is already preloaded, so we'll see how it behaves. The picture below shows the Tamiya spring length (left) compared with a CRC spring. Use a little shock oil or diff oil on the kingpin to allow it to slide freely in the suspension arm. It stops the kingpin 'grabbing' and gives smoother handling. Wipe off any excess as it will gather dust and fluff. Clean and relube every meeting.
Spring comparison



Rear Suspension

  • Ride Height - adjust with the provided axle spacers or the TRG items if finer tuning is required. Aim for 3.5mm to 4mm. Make sure it matches the front end. When fitting the rear axle, don't just push everything up tight to the bearings and clamp up the wheel hub. This will generate friction and heat and could melt the ride height adaptor. At best the car will be slower. Use a piece of backing paper from a sticker as a shim. Insert it end on between the axle spacer and left wheel hub and push everything together and bolt it up. Pull out the paper and you have the perfect gap for a free running axle.
Measuring rear ride height

  • Side damper - don't use the kit greases. I tried both and they didn't 'feel' right to what I am used to. I have used Corally Red damper syrup as a starting point for tonight. I tried 12500 weight diff oil as used on my Speedmerchant but it felt too light.
  • Side springs - I have started with the kit springs. I will see how the car handles before making changes. After fitting the springs to the plastic retainers, a good idea is to add a tiny blob of Evostik where the spring meets the retainer. This reduces the likelihood of losing a spring in an accident. With the car on a flat surface, slowly wind down the side springs until they just touch the pod plate.
  • Centre Shock - I've no idea what weight the supplied shock oil is. Its the same bottle as supplied with my original Tamiya Rough Rider! I've filled the damper with Losi 30wt oil as a starting point. The damper gives a very smooth action. I have fitted the kit centre spring, again to see how the kit parts behave. It 'feels' right, so will most likely stay on. The centre shock is used to basically level the car and stop the chassis dragging on the ground! I'll explain tuning of this in Part 3. For now, all you do is adjust the spring tension to make the chassis level. Once you have set the front ride height and rear ride height, you adjust the shock collar so the middle of the car is the same. This may require adjusting if using different battery packs due to variations in pack weight. My packs have a 30 gram range! There is a little play in the ballstud on the pod end of the shock, so i have fitted an o-ring under the ball cup to remove the slack.
Measuring centre ride height

O-ring added under shock ballcup

  • Droop - this is the amount the rear pod 'droops' below the chassis when you pick up the car. I have been racing 1/12th scale since the late 80's and generally set my pod to droop 1.5 to 2mm. Normally you adjust it by varying the total length of the centre shock. Here, Tamiya have done it for you by moulding an extra lip on to the underside of the centrepivot to act as a droop stop. So, for now we can ignore any tuning via droop (which I do anyway). Basically, if a car has no droop, the rear will go light and you will spin. Note - I did say basically.
Measuring droop when lifting car by centre shock

Tweak

This balances the car up left and right, so that when you accelerate with the wheels straight, the car does not pull to one side or the other.

To set the tweak on the car, you will need a flat surface, two small coins, your 1.5mm allen driver, and a cross head screwdiver. Some people carry out this step with the roll damper disconnected. I never had and I've never suffered adversely.
  1. Place the car on the flat surface with the front of the chassis overhanging. This will allow you to reach the small hole drilled in the centreline at the front of the chassis. Place the coins on top of the front wheels so they are just behind top centre. This makes sure when they fall off they roll backwards onto the flat surface and not forwards, off the table and race across the floor never to be seen again.
  2. Tap the top of the roll mast a few times to settle the suspension on the car. If this is the first time, you'll probably now need to put the coins back on that you have knocked off.
  3. Using the point of the crosshead screwdriver in the aforementioned small hole, gently lift the car and watch the coins fall off. If they fall off together, job done. If they fall off unevenly, screw down the spring on the OPPOSITE side to the first coin to fall by 1/4 turn, and back off the other side the same amount.
  4. Repeat steps 1 to 3 until both coins fall off together.
If you really want to, you can adjust the balance of the car by moving the speedo, receiver and transponder locations whilst the springs are backed fully off the pod plate. Once the tweak is set, secure the electrics fully, and wind the springs down to just touch the pod plate, then carry out steps 1 to 3. Any spring adjustments now will be to ensure the springs are touching evenly, as the chassis is already balanced.

Ready to Race

You should now have a car that has enough ground clearance and is level, is not tweaked and is race legal. Part 3 will cover the initial settings you need to carry out on the track, and the first run of the car. I have already run the car, and its pretty damn quick out of the box!!!

Part 3 is available here http://www.thercracer.com/2013/09/tamiya-rm01x-build-and-review-part-3.html


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