Tyre Testing - 3Racing M-Chassis Tyres

Today was the worst possible day for tyre testing -

Every now and then, the wind turns to blow in from the desert and remind the population of Dubai of the cities desert origin.The best sand storms are brief, 15 minutes of darkness and mayhem as the wind drives a mile high wall of sand across the city.

Today was not like that. Today began with a haze and a wind strong enough to push furniture around the garden. Hours have passed and still no great wall of sand has crashed across the city, but everywhere, inside and outside is covered by a growing film of dust.

Not the best day for tyre testing -

3Racing M-Chassis Tyres
 
I keep A rally car for days like today, it's an M03 with M05 ra uprights, a sport tuned motor and a NICAD battery. The 7.2 volt battery can make the car feel  slow after running my on road LIPO powered cars. As a quick fix I have been waiting for the rally block tyres to wear out so that I can replace them with a set of larger m-grips for a higher top speed.

When I first saw the 3racing tyres, they looked very big. Comparing them with other m-chassis tyres, they are the largest I have seen and so they went straight onto a spare set of rims and the rally car.

Straight on ?

Not really, at over 60 revolutions per second we have to glue our tyres on to keep them on.

Tyre gluing 101
 
1) Wash Everything.

Superglue is incredible stuff, but it won't stick to oil or grease. A lot of RC parts including tyres and the rims are created using molds. In order to be able to remove parts from the mold it is coated with a non stick release agent, if we don't wash this off our parts, paint and glue will struggle to hold.

2) Use The Right Glue

Most glue sold as superglue is a variation of cyanoacrylate, the different variations can work for or against you. If you are gluing tyres with a gap or wedge between the tyre and rim, you can use a thin formula which will run into and around the gap. Thin formulas tend to be fast setting, so if you have a tyre and rim combination that mate without a gap you might be better using a gel formula which gives you time to manually spread the glue between tyre and rim and readjust the fit during the longer set time. 

The 3Racing tyres mate to the rims without a gap and so I used a gel formula.

3) Use A Rubberised Superglue If You Can

If you can find a rubberised formula use it. One of the weaknesses of standard formulas is an inability to flex and withstand shocks. The rubberised formulas are a step towards overcoming this and should perform better in most RC applications.

 
Testing
Testing the tyres was great fun, one of the corners on my test track exits along a wall where a drift of accumulated dust had settled. Coming out of the corner and getting onto the throttle early would get the car power sliding through the dust.
 

Braking was impossible, the car would take upto 10 meters to stop with every speck of dust working as a ball bearing between the tyres and brickwork. Acceleration was reasonable enough, my guess is that the car scrubs the road clean of dust as it claws its way forward.


Tyre Sizes
The 3Racing tyres have a very square edge to them, this gives them the impression of being much larger than other M-Chassis tyres however having measured them they are only 1mm larger in diameter than the popular Tamiya M-Grip tyres.

Tyre	Diameter	Circumference	%
3Racing	60	188.57	109
M-Grip	59	185.43	107
Tamiya Rally Block	55	172.86	100
Slicks (Spice etc)	55	172.86	100

This small difference has a big effect on the distance travelled due to the multiplying factor of pi. The table above shows the diameter and circumference of some popular m-chassis tyres. Taking racing slicks as the standard, the 3-Racing tyres travel  9% further per revolution, while this is a huge advantage in the straights, it can easily be lost in corner grip and especially braking.


So are the tyres any good ? its impossible to say based on todays testing, but the ultimate test of any tyre is in the lap time. As soon as the sand clears I will be out with the personal lap timer for an M-Grip, Rally Block and 3Racing show down.

Fun With The Personal Lap Timer

I still have some bugs and a long 'to do' list, but I have just spent a very enjoyable 100 laps with the personal lap timer. If it has the same effect on my kart driving as it has on my mini driving I will be delighted.

Its the simplest things that are making me happy, for every lap that the timer captures, it makes a beep. If the lap is faster than the current session best, it beeps twice. Its so simple but its amazing how much harder I can work on a lap to get that second beep.

If I get ten double beeps in a twenty lap session, how much better must my later laps be than if I had carried on driving my first lap again and again without the lap timer feedback ?

Duane B

 

Punk Consoles, Lap Timers and IR Transmitters, The 555 Timer

The Personal Lap Timer Infra Red Transmitter has now passed daylight testing - with the aid of a matt black hood for the IR receiver. 

No false laps detected and all genuine laps captured ! 

I know I am late in discovering the 555 timer and the even nicer 556 timer. The web is full of simple, useful circuits using these two chips. Some example applications for RC Include -

As a switched LED Driver, this allows you to drive more LEDs by switching between LEDs so fast that it appears they are all on all of the time, but your power source only has to power some of them at any one point in time !

As an LED Flasher for emergency or track vehicle lights, the same chip is able to switch tens of thousands of times per seconds or once every 10 or more seconds and anything else in between, this makes it ideal for warning lights, police lights etc.

My favorite application of the 555 Timer is the 'Atari Punk Console', look it up, its a nasty sounding little square wave generator that acts as a very crude synthesizer, very little practical use for anything, but its got a cool name and a cool sound.

The 555 is great, but the 556 is so much nicer, for a start its two timers in one package, the pinout is also easier to work with. On the 556 one timer is available through the left side pins and the other through the right side pins this makes bread boarding so much easier.

Personal Lap Timer Transmitter Version 1.0 and 2.0

On the left is version 1.0 using two 555 Timers, version 2.0 on the right uses a single 556 Timer. On the right, you can see the white wire across the IC, this is connecting the output of the control timer on the right side of the chip to the reset pin of the IR Oscillator timer on the left side of the chip. This turns the IR Signal on and off at a frequency we can read on the receiver side, we examine the frequency to confirm that this is a lapping car and not environmental noise.

The current version of the personal lap timer transmitter uses the two timers provided by a 556 Timer IC. The first timer (the IR Signal oscillator), is configured as an astable generating an on/off pulse at 38Khz. This is the frequency required by many popular infrared decoder ICs. The output of this timer drives an infrared emitter LED through a current limiting resistor.

The IR LED has a very tight focus which is great for lap timing. If your looking to build something similar pay attention to the 'view angle' or the equivalent terminology that the data sheet uses to describe the effective signal angle, for lap detection you want as small an angle as possible, for infra red remote control a much wider angle is more useful. 

The second Timer is also configured as an astable, but oscillating at a much lower frequency, I am currently testing 1Khz and 100 Hz versions. The output of this timer connects to the reset pin of the first timer, this causes the infrared emitter to transmit a series of pulses .5ms or 5ms long. On the lap timer side I am looking for pulses in this range, this helps to separate environment noise from actual laps.

If this stage of testing proves successful I will try working with the duty cycle and frequency of the control timer to see if it is possible to create a scheme for determining unique identities for upto 8 cars using a cascade of two or if need be three 555 timers.

Rather than me repeat the excellent work of others I would suggest that anyone interested in more information should have a read through the following links -

Background on the 38Khz IR signal and the ICs Used to detect it see the following link - also take note of the very simple IR Test circuit using just batteries, detector and an LED.

http://www.ladyada.net/learn/sensors/ir.html

There is a nice background on the 555 timer and its different uses and configurations here -

http://www.kpsec.freeuk.com/555timer.htm

There are also a several online 555 Timer calculators that will allow you to find the component values you need to produce a given frequency or period, use your favorite search site and look for '555 calculator'

My current circuit uses -

Control Timer - 

R1 670

R2 8K (3.3 + 4.7 in series)

C1 .1uf

IR Oscillator

R1 220

R2 1K in series with 1K potentiometer to give adjustment from 1K to 2K

C1 .01uf

These values are in part determined by what I had available so just use the calculators to work with what you have.

Finally I should mention that the 555 Timer can generate a lot of electrical noise in your circuits so be sure to use decoupling capacitors if its going to share power with anything else.

Duane B