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RC Car Weight Balance for Faster Speed

Lately I've been obsessed with radio control on-road touring cars. In particular, trying to redesign my current race cars for optimal balance and faster cornering speeds. Here are various layouts and weight balance analysis.

RC Car Tamiya 416 WE

RC Car: Standard Tamiya 416 WE (Normal)

Above is the standard layout found in most high level on-road touring cars (e.g. Tamiya 417, HB TCX, Yokomo BD5, Sakura Zero, etc). Weight balance is 47.79% (front) and 52.21% (rear). Downside is that width from motor endbell to opposing battery is 129mm. Some of the newer models have narrowed it down to 123mm or so (e.g. Sakura Zero, Tamiya TA05v2). Still too wide.

How can we make the car narrower but still maintain good balance? Let's revisit older designs.

RC Car Tamiya 414 Stick Pack

RC Car: Tamiya 414 Stick Pack

The above rc car was the design that won the IFMAR World Touring car championships around 10 years ago. With modern electronics (e.g. lipo battery, brushless motor/esc) the weight balance is 46.72% (front) and 53.28% (rear). Slightly more rear heavy than the 416WE. This surprised me as I thought the weight looked more forward biased. Good thing for scales.

Unfortunately the battery is in a lateral postion and width is 133mm. Might not be a better design than the modern layout.

But... if we use a short lipo pack the width becomes only 96mm. Or a saddle pack lipo. It's looking good.

RC Car Weight Balance Tamiya 414 Saddle Pack Lipo

Above is the Tamiya 414 with saddle pack lipo where width is now only 102mm. That is around 20mm to 30mm narrower than current designs. But enough theory, here is my track analysis of performance.

1. I used a 2010 HotBodies TCX (modern design). It was good, but felt a little sluggish and understeer for me.

2. Switched to my Tamiya 414 (stick pack layout). Turned slightly faster laptimes than my HB TCX.

3. Used a Tamiya 414 (saddle pack layout). Immediately noticed the rc car was much more reactive or nimbler especially on chicanes. I loved the feeling. But laptimes not faster. Maybe I need to adjust driving and setup.

I have concerns on the high center of gravity on the pulleys above the motor and the lack of chassis flex on the Tamiya 414. But so far it has proven to still be very fast on the track.

RC Car Tamiya 416 Drift

RC Car: Tamiya 416 Drift

I read a story where Atsushi Hara (multiple world champ) used a drift chassis layout to win a touring car race. Curious, I did a mock up above and the weight balance was 49.28% (front) and 50.72% (rear). And maybe if I move the battery further to the rear, the balance would probably be same as modern TC layouts.

RC Car Tamiya 416 Inline

RC Car Tamiya 416 Inline

To keep weight centralized and narrow, there are designs where the battery and motor are inline. I like this design, but worried about weight balance. Well nothing to worry about. Pictured above and moving motor and battery further to the rear, the balance is 48.50% (front) and 51.50% (rear).

The inline design is already proving itself in the slower classes where the Tamiya TA06 (inline layout) is faster than the TA05 (modern belt layout) or TB03 (modern shaft layout). Curious to see if this layout will be good in the faster modified tc class.

RC Car Weight Balance Summary

Let's put it all together and compare. The Tamiya 414 with saddle pack has same weight balance to the 416 (and modern tc design), and is 20mm narrower. With modern suspension pieces and adjustable flex chassis, I wonder if it can be faster than current designs?

RC Car Weight Balance Analysis

Hope this helped you out in your own quest to design a better radio controlled touring car. Of course, besides weight balance layout, other design considerations to keep in mind:

1. Roll adjustment. Ability to tune the front and rear roll centers.

2. Chassis flex. Ability to stiffen the front and/or rear of the chassis to add or reduce grip.

3. Center of gravity. To keep layout and parts as low to the ground as possible.

4. Front and rear drivetrain drag and response. A gear driven transmission will instantaneously transfer power to the tires. A belt transmission will absorb some of the initial shock and be smoother on the tires (maybe good for modified motor class). Balance of front and rear response to motor power.

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