I found the Subaru Blueprint a long time ago on the web  – not sure who deserves the image credit. If anyone knows let me know.

You can purchase pre-build lighting sets from a lot of manufactures – which offers an easy way to get you started. Alternatively you can build your own lights for a fraction of the cost and likely with a lot more output and brightness. In my previous post I build headlights for my Tamyia DF03RA Subaru Rally car. The next logical step is to add rear lights and brake lights.

The rear lights are rather straight forward – just get some red LED’s wire 2 (one for the left side and one for the right) in series and add a resistor in series to not fry them when connecting to your rc cars battery. Remember LED’s always need a resistor and the size depends on your LED.

Building brake lights for your RC car is a bit more tricky. Most commercial rc car brake light kits only come on when you are actually pulling the trigger backwards into braking position. This may work for some but not for me (and the rest of our RC Rally Group) who races on nicely flowing backyard rally tracks (we have 4 on Maui/Hawaii  now) where we do not really use the brake but go off the throttle a lot and coast through corners. Slamming on the brakes on a gravel – loose soil track would unsettle the car way too much. Plus the drag of the rc car motor acts as brakes anyway.

My solution to the “brake lights on” when off the throttle and slow coasting is to use a Zener Diode attached to the motor plus lead (important this only works with brushed motors) and to have the breakthrough voltage of the Zener Diode activate a transistor which will essentially offer the electrons a way of less resistance and therefore turn off the brake lights. Or in other words – the rc car brake lights are on when the car is at a stand-still and will remain on until 4 Volts a measured at the Motor Positive lead. The 4 Volts are the breakthrough voltage of the Zener Diode. When I go off the throttle the voltage at the Motor positive lead falls under 4 Volt and the brake lights come on again.

Below is the circuit diagram which makes the brake light switching a little more visual.

Important Notes:

• Works only with Brushed Motor
• Resistor R1 protect the Zener Diode
• Use a bigger (higher Voltage) Zener Diode to have the brake lights come on earlier.
• Resistor R3 needs to be bigger then R2
• Resistor size for R2 and R3 depends on your LED voltage and current

Picture of RC car brake lights on under coasting and when going off the throttle:

Ever since we started Rally Cross racing our RC cars in our homemade backyard Rally tracks we knew that we had to race in the dark at some point. If you are following my blog you may know that I am not a big fan of buying off-the-shelve products to solve those fun engineering challenges.

The first stage in my RC car Rally Lights project was to build a simple prototype LED headlight array that would attach easily to the car. I opted to use Lego Technic pieces because 5mm LED’s fit perfectly. Plus if you drill out the pieces just a little bit you will find that they fit very nicely onto standard body mounting posts.

This LED Remote Control Car headlight array connects to the cars main battery and uses 6 White 5V LED’s. 2 Led’s are wired in series with a 100Ohm resistor for each of the three pairs. The setup is a bit on the “hot” side as far as the resistor size goes, which means the LED’s may not live as long as they could if they had a bigger resistor. I also added a simple on-off switch.

As mentioned I opted to mount the lights on top of the car so that they can be easily removed for day time racing. Another advantage of clipping the lights onto the body mounting posts is that the lights don’t vibrate and flex as much as they would be when mounted to the lexan body itself. Although, I must say that my friend running an HPI Rally car had his lights mounted into the body and the vibration was not as extreme as I expected.

If you are owning a Tamiya DF03RA Rally kit you will receive nice reflectors and masking stickers that allow your car to have very nice very nice integrated head and taillights. However, the Tamiya stock setup only allows for 2 lights and the lighting kits sold in stores tend to be more for looks then for actual racing in complete darkness. I tried keeping my lights brightness and range to scale – based on the Subaru night super stages lights that attach to the hood for the Australia and Sweden rally, however first tests show that I have to go above scale with brightness to make the RC car really usable on a tight track at night.

My next project will be to add brake lights and tail lights. If you buy a brake light kit for your RC car you will notice that the lights only come on when you are actually using the brake on your radio control, however if you are using drag break with your brushless setup or are using a brushed motor with a bit of drag you may never use the brakes – especially when driving on a nice flowing rally or rally cross track like we build. What I will do is design a circuit that will look at throttle and motor rpm’s and trigger the brake lights accordingly.

I identified 4 major needs:

1) Easy to activate – but waterproof On-Off Switch

2) Totally sealed Body and Chassis that does not let any dirt in

3) Easy access to Charging Port/Plug for Batteries

4) Bigger Bumper to prevent Wheel and Suspension damage

The best solution was to integrate those with my Mud and Dirt Electronics Cover based on the Tamiya Dark Impact Body

And here is the RC car in its parking lot and charging bay in the shed. This reduced the setup time to run the car from 10 minutes to under 2 minutes.

Yes we are taking about driving our precious RC Car in the mud, rain and through big puddles of water. We don’t have snow where I live but I would love to do that too (Sweden Rally anyone).

The big problem is that the tub of the rc car will fill up with a bunch of dirt and water in no time at all. On my backyard track I have to dump out the car after 5 laps because it is filled up with dirt. I initially tried building my own electronics dirt and splash cover but results where less than stellar. The big question you may ask is why not use the Tamiya “Dark Impact” body as cover. Well A) I did not know about it initially – although a quick google search would have revealed it and B) once I did find out I was simply to cheap to blow $35 bugs on a piece of plastic. Needless to say I finally got over myself and ordered one on Ebay.

I read a bunch reviews regarding the Dark Impact Buggy and quickly learned that the number one complained was that the car fills up with dirt – which told me I can’t just cut along the lines that Tamiya suggest to trim the body to fit. I carefully cut away one plastic piece at a time to make sure I cover more open spaces compared to Tamiya suggestions.

Picture below: Test driving the Dust and Dirt Cover based on the Dark Impact body:

One concern is of course heat. Having a tight fitting body is awesome  – but that also means that there is zero airflow inside the body. People with high performance brushless setups will run into trouble here. Thank goodness I flooded mu Brushless setup and only have the stock 520 motor and electronic speed controller (ESC). Which means heat is no problem when I let my car cool down every 5 laps. 5 laps turns out to be a good number to run on my track just feels right to do five laps then pause look at lap times and go again. A bit like Rallycross events if you will.

Anyway, so the reviews talk about dirt getting still in, which meant I have to do a bit extra trickery to keep my car “clean” on the inside. One thing I did was fill the sidepods with styrofoam – this will prevent any water that makes it in from getting trapped. The white styrofoam is also good fro quick inspection through the window of the car – cause it is white.

No most expensive part in my receiver – so I really wanted to get it out of harms way. I ended up mounting it to the roof of the Dark Impact body inside its very own plastic cover. By the way the plastic covering the ESC comes from a jewelery box from HotTopics (thank god for girl friends and wifes). One concern was that the cables are getting destroyed by the exposed driveshaft. What I did is simply mount a piece of plastic and screwed it into the original antenna mount.

The body itself is screwed onto the tub. I know that a lot of people use Velcro  – which I am sure works fine. But I liked the idea of nuts and bolts seemed cleaner, stronger and easier in the long run. By the way the nuts are held on the inside with hotglue in position.

Here is a picture showing the styrofoam, ESC mount and cover as well as driveshaft prtection:

Turns out it is a lot of fun to drive the Tamiya Df03RA chassis with just the Dark Impact cover. Less weight and a lower center of gravity make for fun and exiting driving. However nothing beats the look and size of the Subaru Cover on top of it. So I guess it is performance versus looks. Just like in the real world. I will post lap times comparing the Dark Impact with rear Wing, without rear Wing and of course with the Subaru body.

Here is how the Dark Impact body looks inside the Subaru body. I was surprised just how small it is.

(too bad I misspelled Tamiya…)

The following article will compare the Tamiya Subaru 1/10 scale model versus the real Subaru Works Team entry. The scale model is really close in scale. Well done Tamiya.

All measurements are in metric – we are talking engineering here. The data comes from a variety of sources. Please leave a comment if you have more correct numbers.

Cost:

Subaru Impreza WRC 2007 | Works Team entry build by Prodrive/UK :  Est. $750,000

TAMIYA DF-03 RA Subaru Impreza WRC 07 : MSRP $332

Cost in Scale: $332 x 10 =  $3320

Model to Real Car Difference: – $746,680

Length:

Subaru WRC: 4465 mm

Tamiya: 445 mm

Model in Scale: 4450 mm

Model to Real Car Difference: -15 mm

Width:

Subaru WRC: 1800 mm

Tamiya: 184 mm

Model in Scale: 1840 mm

Model to Real Car Difference: -40 mm

Height:

Subaru WRC: 1390 mm

Tamiya: 193 mm

Model in Scale: 1390 mm

Model to Real Car Difference: +/- 0 mm

Wheelbase:

Subaru WRC: 2535 mm

Tamiya: 266 mm

Model in Scale: 2667 mm

Model to Real Car Difference: + 132 mm

Wheels (Rims) for Gravel :

Subaru WRC: 15 inch (Tarmac Wheels: 18inch)

Tamiya: 1.96 inch

Model in Scale: 19.6 inch

Model to Real Car Difference: + 4.6 inch Gravel (1.6 inch Tarmac)

Tires for Gravel :

Subaru WRC: 225/60

Tamiya: 31/8

Model in Scale: 310/80

Model to Real Car Difference: + 85/20

Weight:

Subaru WRC: 1230 kg

Tamiya: 1.8 kg

Model in Scale: 180 kg

Model to Real Car Difference: – 1212 kg

Engine Kwh :

Subaru WRC: 224 Kwh

Tamiya: o.5 (stock 540 Mabushi Motor @ stall)

Model in Scale: 5 Kwh

Model to Real Car Difference: -219 Kwh

Engine Bhp :

Subaru WRC: 300 bhp

Tamiya: 0.65 bhp  (stock 540 Mabushi Motor @ stall)

Model in Scale: 6.5 bhp

Model to Real Car Difference: -293.5 bhp

Power to Weight Ratio (kg to bhp) :

Subaru WRC: 4.1 kg/bhp

Tamiya: 2.76 kg/bhp   (stock 540 Mabushi Motor @ stall)

Model to Real Car Difference: + 1.43 kg/bhp

0-100km/h | 0-60mph :

Subaru WRC: 4.8sec

Tamiya: ____

Model to Real Car Difference: ____

I did a Front Wheel drive test a while back, impressions and lap timing results are available here. Now I finally had the time and most importantly consistent track conditions to run the Tamiya Subaru in AWD and RWD on the same day back to back.

In order to change the rc car to rear wheel drive only I simply removed the front drive shafts as shown in the picture below.

Granted that this does not produce the optimum performance compared to removing the main drive shaft and therefore eliminating the friction drag considerably, however it is quick and easy and allows for the rc car to be converted back to All Wheel Drive in a matter of minutes.

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The Results:

Driving a Tamiya Subaru DF03-RA in rear wheel drive is a lot of fun -but challenging at the same time! Laptimes where 3 seconds slower compared to the All Wheel Drive configuration. Interestingly, the Front Wheel Drive configuration was only 2 seconds slower then the All Wheel Drive lap times.

All Wheel Drive

Fastest Lap | Avg Lap | Total

12.908 | 15.410 | 1.16
12.217 | 19.552 | 1.38
13.580 | 17.362 | 1.27
11.626 | 13.429 | 1.08
11.746 | 18.612 | 1.33
11.997 | 15.550 | 1.16
13.409 | 14.969 | 1.15
12.848 | 18.150 | 1.31
12.107 | 14.879 | 1.15
12.377 | 13.833 | 1.10
12.608 | 23.858 | 2.00
11.907 | 15.954 | 1.20
12.778 | 16.936 | 1.25
11.656 | 14.857 | 1.14

12.411 | 16.667 | 1:26 | Session Averages

Rear Wheel Drive

14.330 | 22.446 | 1.55
15.462 | 23.668 | 1.59
16.423 | 20.761 | 1.44
15.392 | 23.970 | 1.56
15.732 | 19.484 | 1.38
16.734 | 23.230 | 1.56
15.622 | 22.382 | 1.53
15.772 | 19.758 | 1.40
14.390 | 24.997 | 2.06
15.612 | 17.665 | 1.29

15.569 | 21.836 | 1:53 | Session Averages

After several laps of getting used to the new handling I was actually able to turn faster lap times compared to the Brushless motor thanks to the new found “breaks” that allow me to get of the throttle later.

I have to investigate if there are Electronic Speed Controllers for Brushless motors that would allow me to adjust the coasting (breaking) resistance when letting off the throttle.

The car is much to light in the front (which was clearly visible right from the start) for making it a serious front wheel drive contender. I did not have the chance to run the front wheel drive configuration on tarmac, things might look different there.

One of the positive aspects of having the Subaru in front wheel drive was the noticeable amount of understeer in tight corners, which I was able to maneuver with more precision under high speed as compared to the all wheel drive configuration.

Below are the track times of the day, I alternated between all wheel drive and front wheel drive to get representative results that takes track wear and tear over the duration of a session into consideration.

All Wheel Drive
Fastest Lap | Average Lap | Total time 5 Laps
12.970 | 16.549 | 1.23
13.248 | 16.519 | 1.23
13.960 | 16.490 | 1.21
13.779 | 17.597 | 1.29
13.649 | 17.780 | 1.26
12.928 | 16.617 | 1.24
13.422 | 16.952 | 1.24 Averages

Front Wheel Drive
13.329 | 15.960 | 1.22
14.681 | 32.640 | 2.44
14.350 | 19.130 | 1.35
15.462 | 25.837 | 2.10
16.313 | 23.255 | 1.57
14.430 | 21.358 | 1.47
15.352 | 19.948 | 1.40
14.845 | 22.590 | 1.65 Averages

Conclusion: The front wheel drive configuration was roughly 1.4 seconds of the pace of the all wheel drive config. The average and total lap time numbers are not representative due to the fact that the vehicle got stuck in almost every 5 lap heat.  I will run the car in rear wheel drive configuration as soon as time and conditions allow.

The difference of 1.4 seconds equals to an average speed difference of 10.6km/h with all wheel drive and 9.6km/h for the front wheel drive car.

During a 5 lap race on a 39.6 meter long track the difference in speed accounts for a 7.1 seconds difference at the finish line.

See this post on how to calculate average speeds of a moving objec

I posted earlier how to calculate gear ratios and top speed. I also compared  the RPM’s and MPH of Tamiya’s stock motor with a Brushless motor.

Here is the math to figure out the average speed:

Average Miles Per Hour

Average Speed = Total Distance divided by Total Time

D = distance (length of the track) in feet = 130 feet
T = time in seconds  = 14.716 seconds (based on 4 test days and 3 race days)
S = speed in miles per hour

To convert seconds to hours use 3600 (because there are 60 seconds in a minute and 60 minutes in an hour)
To convert feet to miles use 5280 (because there are 5280 feet in one mile)

S = 130 feet / 14.716 seconds = 8.83 feet per seconds

8.83 feet per seconds x 3600 = 31788 feet per hour

31788 feet per hour / 5280 = 6.02 miles per hour

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Average Kilometers Per Hour

Average Speed = Total Distance divided by Total Time

D = distance (length of the track) in feet = 39.62 meter
T = time in seconds  = 14.716 seconds (based on 4 test days and 3 race days)
S = speed in kilometer per hour

To convert seconds to hours use 3600 (because there are 60 seconds in a minute and 60 minutes in an hour)
To convert meter to kilometer use 1000 (because there are 1000 meter in one kilometer)

S = 39.62 meter / 14.716 seconds = 2.69 meter per second

2.69 meter per second x 3600 = 9692.3 meter per hour

9692.3 meter per hour / 1000 = 9.69 kilometer per hour

Today was the first day the car went on the backyard track.

.

Good News:

• Car handles like a champ
• Surprising off-road capabilities even in soft gravel
• Plenty torque and still enough speed using a 7:1 ratio and Brushless Novak motor

.

Bad News:

• Track is too narrow in some areas
• My lower chicane is too tight for the steering radius of the Subaru
• Track is a bit short
• Speed Controller and Receiver dust cover still let’s to much dirt in

In order to make the chassis a little more “Rally friendly” – which means running in wet and/or dusty conditions I decided to build a plastic cover.

I am using a thick-monofilm available in most arts and crafts stores. When designing your own cover make sure that your ESC (Electronic Speed Controller) still gets proper cooling or you are running the risk of overheating your ESC.

Detailed images below.

Tamiya Rally Car RC Dirt Cover Side View

R/C Rally Car Dirt, Dust, Mud and Water Cover

R/C Dirt and Dust Cover - almost looks a little bit like a Formula 1 car

Tamiya Offroad Dirt, Dust, Mud, Gravel, Water Electronics Cover Front View

UPDATE:

I finally bought a Dark Impact body to be used as Dust Cover. Read all about it here.

The motor is produced by Mabuchi Motor Co. LTD, based in Japan. If you would like to know Voltage, Speed, Efficiency, Watt etc. to calculate your R/C cars speed and performance then this official 540 Motor product spec PDF might just what you are looking for.

You may need Adobe Reader to view the file.

Not sure what to make out of these numbers and how to calculate how fast your R/C car, buggy, truck should go? Look here.

Here is the All-in-One formula:

Please Note that Your R/C Car will not achieve these speeds!

These numbers are the theoretical calculated speeds.

Gearing Ratios

Driver Ratio (aka Spur/Pinion Ratio) [-Equals-] Spur Gear [-Divided by-] Pinion Gear

Example: Spur Gear 75T / Pinion Gear 32T (T stands for Teeth – if you are not sure how many teeth your gear has, just count them).

75 / 32 = 2.34 | The Driver Ratio is 2.34, which means that the Spur Gear will turn 2.34 times, while the Pinion Gear turns 1 time.

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Internal Gear Ratio (aka Transmission Ratio) [-Equals-] Final Drive Ratio (found at the wheels) [-Divided by-] Driver Ratio (aka Spur/Pinion Ratio)

Example: Final Drive Ratio 7.16 : Driver Ratio 2.34

7.16 / 2.34 = 3.06 | The Internal Gear Ratio (often pre-set by the manufacture) is 3.06

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Final Drive Ratio (aka Overall Gear Ratio found at the Wheel) [-Equals-] Internal Gear Ratio (aka Transmission Ratio) [-Multiplied by-] Driver Ratio (aka Spur/Pinion Ratio)

Example: Internal Gear Ratio 3.06 x Driver Ratio 2.34

3.06 x 2.34 = 7.16 | The Final Drive Ratio is 7.16, which means that the Motor will turn 7.16 times, while the Wheels will turn 1 time.

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Theoretical Maximum Motor RPM

Electric Motors are often rated with a KV number such as 4300 RPM/Volt DC

In a very simplified way this means the motor will turn 4300 for each Volt applied. Motors are rated for a certain maximum Voltage which consequently limits the maximum RPM.

Example: The Novak SS 4300 Motor is rated 4300RPM/Volt DC with a maximum Voltage of 7.2 Volt.

4300 RPM x 7.2 Volt = 30960 | The motor has a theoretical maximum RPM of 30960, in other words the motor turns 30960 times in a minute.

Tamiya’s Mabuchi 540 Stock Motor has a maximum RPM (Rounds Per Minute) of 23400.

Please note that the RPM under load (meaning once the motor is in the car working hard) is lower than the calculated maximum RPM.

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Wheel Diameter, Circumference and Travel distance for each turn

Wheel travel distance (meaning how far does the car move forward each time the wheel turns) depends on the size of the wheel.

Wheel size is easily measured with a Ruler. Just measure the overall outside diameter.

Example: The Tamiya Block Rally Tire measures 6.8 cm, which means the outside diameter is 6.8 cm (2.6 inches)

To calculate how far the wheel travels per turn simply multiply the Diameter with Π (Pi 3.141)

Example: 6.8 cm x 3.141 = 21.35 cm | Meaning the wheel travels 21.35 cm (8.4 inches) on each turn.

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Theoretical Maximum Top Speed

How fast should my car go? Based on all steps above we can now calculate how fast our car should theoretically drive.

Step 1) How fast do the wheels turn based on maximum motor RPM?
For this we will use the Tamiya Stock 540 Motor with the assumption that it will turn 23400 rpm’s. We also assume that we are running the out-of-the-box Spur and Pinion which comes with the model, resulting in a final gear ratio of 7.16. We now need to divide the motor rpm by the final gear ratio.

Example: Tamyia Stock 540 Motor at 23400 RPM [-Divided by-] Final Gear Ratio 7.16 (found at the wheels).

23400 RPM / 7.16 = 3268 | Which means the Wheels turn 3268 times per minute

Step 2) How fast and how far does the car travel per minute and hour

We calculated earlier that the car travels 21.35 cm (8.4 inches) per turn. We will nnow figure out how far the wheel will travel each minute based on our RPM calculated above. To make it easy we will first covert cm into meter 21.23 cm / 100 = 0.213 m

Example: 3268 Wheel RPM’s (-multiplied by-) 0.213 m tire circumference

3268 RPM  x 0.213 m = 696 | Which means the car will travel 696 meters every minute

Lets calculate meters per minute into meters per hour by multiplying with 60; because there are 60 minutes in one hour.

696 m x 60 = 41760 | Which means the car travels 41760 meters in one hour

Lets calculate meters into kilometers, which is done by dividing through 1000; because there are 1000 meters (m) in 1 kilometer (km)

41760 meters per hour / 1000 = 41.75

Which means the car has a theoretical calculated top speed of 41.75 kph or 25.94 mph

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The complete formula with all steps above would look something like this:

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Take a look how the top speed changes with different gear ratios here.

There are several R/C car manufactures, all of which produce great products in their own right. Many manufactures produce On-Road RC cars with optional Rally car body’s. These vehicles are a blast to drive on the street but do little good on fine gravel or packed dirt mostly due to the fact that drive-train and steering are not adequately protected. Ride height is another issue. On the other end of the spectrum are offroad Buggies and Monster Trucks, often powered with powerful nitro engines that make your lawn mower jealous.

My personal model building preference is detail and authenticity, which essentially limited my choice down to the discontinued HPI RS4 Rally and Tamiya’s DF03 RA. Both models offer roughly the same feature, with the big difference being that the HPI model is discontinued and hard to find. I own already two Tamiya touring cars, a 1/10 Opel Astra DTM on a RC TRF415 Electric Chassis and a 1/8 Opel Calibra on a TGX Nitro Chassis both performing and looking great.

I will build the model initially with the Stock Motor and Gear Ratio. But will later on install a Novak 4300 Brushless Motor.

Batteries used are Intellect 4600mAh

Remote Control is a JR Racing XS3 Pro