A Tale of two Chassis

I can't resist a little bragging here. After the podium photos for the first night were finished, I asked if I could flip the cars over and take a photo (the one on the right above). Click on it to expand and have a look at the chassis. My chassis are pretty successful in this class!

Anyway, this post is about two chassis for the Maserati, so back to that:

The solid option:

There is no reinventing of any wheel here. It's just a basic one-piece design using my default "low weight" philosophy. By "low weight" I mean both low in terms of grams and, more importantly, low in terms of height above the track. The most significant weight in a slot car (before adding ballast) is the motor. Therefore I always use an offset crown gear to get the motor as close to 1mm above the track as I can. In fact, for the last few months I have been trying to develop printed gears to achieve this aim. I'm getting there slowly. The main issue has been finding a material that will give me reasonable durability. So far, ABS seems to be the most successful. I've been running a 2.5mm offset ABS crown in my Super Squalo Ferrari for four race nights and its standing up to an 18K Predator motor very well and has a very, very smooth mesh. The next test will be to use one of those crowns with a faster/torquier motor.

The other advantage, as well as low C of G, of the offset gear is that you can use a larger diameter tyre. This may seem of little value until you remember that the rules for this class specify both motor speed (12.5K) and gear ratio (3:1). So the only remaining variable that affects top speed is tyre diameter. The circumference of a 19mm tyre is 59.69mm. The circumference of a 21mm tyre is 65.97mm. So, for every rotation of the rear wheels, the car with 21mm tyres will travel 6.28mm further than the car with 19mm tyres. 10.52% further. In a hobby/sport where we're always looking for the one-percenters, offset gearing is, to my way of thinking, the better way to move the motor weight lower rather than grinding your tyres down to get less ground clearance (resulting in a lower top speed).

You can see in the photos that I added about 10 grams of ballast to increase the smoothness of the handling.

To summarise this chassis.... this car, fitted with this chassis, is probably one of the sweetest handling slot cars I have ever driven. The very low body, pretty long wheelbase and short rear overhang probably also contribute significantly to this great handling.

The pod option:

When I first saw photos of the MR Slotcars Corvette chassis, I really liked the way that it seemed it would pivot around the front and back pod mounting points with the side mounts controlling that pivoting. That may not have been Mr Mossetti's design philosophy, but that's how it appeared to me and I liked it.

But, thinking more about it, I thought "if it's going to pivot, wouldn't it be better if it rotated around the centre of the back axle?". So I drew up a chassis and pod that have a rear pin on the chassis and a front pin on the pod, slotting into a hole in the back of the pod and another on the chassis in front of the pod. The front mount hole (on the chassis) is split with the lower half printed on the chassis. The top half is a cap (purple in the first two photos above) which screws to the chassis and locates the pod. So removing the pod only requires undoing this two screws and lifting off the cap.

Then, to control the pivot/rotation of the pod, I raised the side "wings" and made room for a printed spring under each. The springs are red in these photos. I can vary the compression of these springs, if needed, by altering the thickness thereof. The pod rotates around its axis very smoothly and returns to centre softly.

Again applying my "low weight" dogma, this pod uses a 2.5mm offset crown gear. I made this chassis to compete, as closely as possible, with the MR Slotcars Corvette and the further cool GT models that he has in the pipeline. So it uses an 18K slimline and 10:24 gearing the same as MR. Those cars use Slot.It offset gears, so I'm assuming that they run about a 1mm offset. Slimline (FF-050) motors are pretty light but very low in height, so I figure that every millimetre lower I can place the motor will have a significant effect on handling. You can see, in the small photo above, how the bottom of the pod hangs well below the chassis.

After I am fully convinced that ABS is a durable option for my gears, I will experiment with 3mm and 3.5mm offsets. Might work, might not. But I won't know if I don't try. But, as it stands now, the motor could be at least 1mm -1.5mm lower than it is. I know I could use smaller diameter tyres, but that would reduce the top speed.

Or, who knows, testing and racing might show that it handles just fine as it is. Frankly, so far, that is the case.

Until next time... when I'll probably be writing about a very sexy classic Le Mans car that I'm finishing at the moment.

Cheers, Peter