Fault tracing poor brakes

Squeezing out those last few tenths

Fault tracing poor brakes

Postby wixwacing » Fri 18 Jul, 2008 11:58 pm

Interesting topic this, because good or poor brakes can turn you from hero to zero in a four way (or more) fight. I like to race some of my eighties Scalex and MRRC F1's on the local board tracks. These cars have the small Johnson 111 motors in them, and, whereby they have the power to be competetive on the twisty tracks, they need to be pulled up thirty or fourty centimetres before their 'S' can cousins because of poor brakes, loosing position going into bends.

Carrera models old and new have inherent brake problems. Firstly, the onboard noise reduction components. Secondly, early cars are handicapped by their final drive ratio and rear wheel diameter. Later models, even though they have a 3 : 1 final drive, can still have rear wheels in excess of 22 mm diameter when others are 20 to 21 mm! Next is the state of motor tune.

Carrera 'S'cans seem to have a higher state of tune than Scaley and Fly P1 motors. This might be achieved by reduced windings and thicker wire?? Long armature motors like Ninco NC5's, SCX motors etc are very good generators due to the extra lenght of their armatures and the extra wire in their system. The high reverse emf on braking is countered by the magnets to give this good braking characteristic. Shorter arm type 'S' cans don't generate as much reverse emf proportionally at the same revs and the higher spec the motor, the less braking they will have. The only way to improve this is by either replacing the motor with either a lower spec motor or one with better characteristics or altering the gear ratio to overdrive the motor more on braking.

In the case of the standard Carrera motor, I have found the best solution to be to up the 3 : 1 ratio by changing the crown gear to a 28 or a 29 tooth contrate. This overcomes the overgearing caused by larger rear tyres/wheels and contributes to braking by trying to spin a passive motor that much faster for the same model speed.

Lastly, the final items overlooked by most are the controller and track connections. If you are running on a plastic track and experiencing poor braking away from the power source this could well be attributed to the compounded reduction of conductivity at each poor joint. Short arm motors will be more susceptible than their longer armatured cousins. Similarly, a short armature motor is less sensitive to power loss at the extremities of a track than are long arm motors which may struggle more in a minefield of poor connections. They require more current and the track connections are presenting a greater resistance to their demands.

Lastly and by no means leastly! The hand controller connections are critical. Not only outside but INSIDE too! Some makes of controllers use the pivot points inside the controller as part of the brake circuit! If these or the sliding contact areas are dirty or conducting badly you will experience poor braking here also, especially the higher spec short arm motors.

So, don't just look at your model when fault tracing performance or braking problems. Unless you are fully convinced everything else is fine you must check out all the potential problem areas from transformers to braids and everything in between!!
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