Cartrix disasters

How DO they do that??

Cartrix disasters

Postby wixwacing » Mon 09 May, 2016 5:03 pm

Right from day one of this fabulous hobby there has been a litany of spectacular and expensive model failures. In the early days there was an over expectancy of a models durability and sure enough, trends emerged against which precautions could be taken just to prolonged a models life. In the early days of RTR models it was loose wheels, and many a model would slide to rest on three wheels in the middle at a critical juncture in the competition. Others would see rear axles break loose in unavoidable one on one contact. Less serious events could be as simple as decorative parts becoming detached eventuating in a small bag of loose spares being collected from around the track.

But as time has moved on it is hoped that the major manufacturers have overcome these unnecessary occurrences and so they have……mostly! But there are still ominous events lurking in the dark which will pounce on you when you least expected it or wanted it. We still have RTR models which shed the odd wheel; and some that pop their guides just when you didn’t need it. Others may have their motors pop out of their mounts, or in the case of front motor models, the centre drive/tail/prop shaft springs from its bearing. We also have plastic pinions splitting and letting the car scream to a standstill on the main straight, guides which shed their lead wires because the receptacle on the guide has split down the side relinquishing any grip it may have had on the wire in it; but in spite of all this we soldier on, eventually replacing most of the defective parts with superior after market spares, rebuilding the model from the ground up.

But there are still defects in these models which should have long since been addressed, In particular I am thinking of the Cartrix range of models, great historic GP cars which are a great class to race and which look the business on the track and in competition. It is ever apparent that although a great looking model, they still have some serious faults which they should not have. I am talking of motor and axle mounts. Going back to when they were first produced they had a somewhat dated but acceptable ‘clam-shell’ type body similar to Scalextric cars from the sixties. And back then, the bodies were (and still are) poor fits with large unsightly gaps around the body joints; but these early racers did, and still do have robust motor and rear axle mounts. Now, if we were paying a reasonable amount for this kind of quality we would probably accept them for what they are. But we aren’t

The price of Cartrix models have almost doubled since those early days and you can expect to pay up to 30% more for them than you would a good mainstream model, and get this, the motor mounts and axle mounts are thinner than the original models, and as such, are susceptible to regular failure, sometimes not even on the track!! So much so that not only have I seen these mounts fail while owners are servicing their models on the bench, I have also had the dubious honour of having to fix a model which had both a broken axle mount AND a broken motor mount fresh from the box. Unfortunately these models are acquired from overseas and the cost of returning them (shops won’t pay return freight on warrantable items) is prohibitive to say the least. Also, I am not aware that Cartrix offer the option of a body/chassis part as a spare!

So where do we go from here? Well having just had the rear axle fall out of my Supersqualo and a Lotus 16 grind to a halt, I took the matter into my own hands and effected what is hopefully a reliable repair. I have made it as simple as possible but it does require a certain level of modeling skills, but hopefully the average racer may be able to make use of this handy fix. So if you have a Cartrix classic GP car waiting for surgery…..read on!

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The idea is to create a bracket which is easy to make and easy to fit. The bracket I have made certainly works and there is no loss of performance. First up is to make the bracket in flat form, after having taken several measurements from the motor and axle I devised a ‘U’ shaped bracket that is soldered half way up the motor. The bracket has facility for an axle tube and apart from removing the original broken axle mount, no other parts need to be removed. In this case the assembly clips back into the original motor mount and the clamping effect of the two body parts holds the rest together

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The flat bracket has to be curved to match the body, this I achieved by clamping the bracket lengthways in a vice along with a large diameter drill bit. The bracket was then bent to match the radius of the drill bit and after offering up against the motor, a final matching radius was achieved. Before soldering the distance to the axle has to be calculated so there will be enough clearance between the contrate and the pinion shaft

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The contact faces of the bracket and the motor will need a good scrub clean to allow the solder to work quickly. The bracket is lightly clamped to the motor and after checking alignment, the bracket is soldered through one hole to start with. Any alignment adjustments can be made at this stage, and when happy, the second arm of the bracket can be soldered ensuring the axle tube is at 90° to the motor shaft. I used a 100w soldering iron so I could be ‘in and out’ and not pump too much heat into the motor casing. I recommend no less than a 75W iron and again solder as soon as possible. If you don’t get it right first tiem, cool the motor down (water) and try again. There should be no adverse effects heating the motor in this way as magnetism returns to normal levels as the motor cools. This applies to temperatures in excess of what the average soldering iron produces. After the brackets are soldered, finely adjust the bracket and solder in the axle tube.

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Once happy with the alignment cut the axle tubes to size. I recommend the overall width to be slightly shorter than the gap between the wheel inner hubs. The centre piece is cut away and the ends of the new arms can be reprofiled if you have a dremel style tool. The bottom edge of the bracket may need some attention to allow it to sit low in the body and to have the motor mounts fully engaged. Try a dummy axle in the tube, if there is any binding you can alter the tubes until the axle rotates freely.

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Note the original axle mounts have been removed from the body and the axle tube initially trimmed to length ensuring the tube is centre and at right angles to the motor shaft. This I cannot overstress.

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Note the slight mod to the motor aperture, on the next one I will trim the brackets to size instead

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The motor sits comfortably in the chassis. The body may need a slight trim where the axle tube leaves the body.

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Gears reassembled; don’t forget to lube everything before refitting the top! You may find the splines on the axle shaft are tight in the tube. Don’t force them as you will bend something. File the splines down till the axle slips snuggly through the tube. There should be enough spline left to fix the contrate firmly, after all it is only an NC1 style motor we are dealing with. If you do have problems with crown wheel slip, discard the original crown gear (25z) and replace it with a grub screw fixing type.

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So that’s it, I have given my Lotus a good workout and it shows no sign of loss of power or other defects. Remember, it is essential to solder the axle tubes in alignment to avoid drag in the transaxle setup.


Materials are :

Brass strip 19 x 0.35 (3/4” x 1/64”)
Brass tube o.d.1/8” – i.d. 3/32”

Let me know how you get on!?
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When I'm not racing slotcars,
I'm out in the back yard, burning food!!

When I win, it's because of my talent, not my car or my controller!
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