Scalextric Mercedes-Benz 300 SLR build

[Audi1]

I've started another build for an upcoming proxy. It's based on a Scalextric Mercedes-Benz 300 SLR, the car that sent Mercedes out of the motor racing scene for almost 30 years; following the devastating crash at Le Mans in 1955. Bill (mcliams) has recently built a model of this car (the #20 car) and entered it in the ROAR proxy. After looking it over, I decided to give it a shot, too. I like the marque and it seemed like a reasonable car for this proxy.

As with several of the Scaley cars in the classic line, this one has the rocker panels attached to the chassis, instead of on body. Since I was concerned about being able to get reasonable body float with this structure, I decided to migrate them off the chassis and onto the body. Here's a picture of the chassis with the rockers cut off:



I screwed the body back onto the cut chassis and tack-glued the rockers on with thin CA, using tape to hold the rockers in place against the chassis. Then I backed the CA with my favorite plastic-to-anything glue (Loctite 389 - thank you, Chris Walker (chrisguyw)!). Then I mixed up some 30 minute epoxy and used that in conjunction with 1.0mm plastic strips, to strengthen the rocker joints:





After setting up for 24 hours, the result was pretty strong and the look was OK:





I was planning to put a Slot.It HRS2 chassis under the car, but there wasn't enough width to do it without a big chance of binding the tires on the wheel wells. So, I went a different way; one that I haven't tried yet, a PCS chassis. The first thing I wanted from this chassis, that doesn't come stock on it, was front axle adjustability. So, since the PCS chassis has the front axle mounts outboard, I used them as anchor points to add some cut-down SCC front axle blocks. It gives a good amount of surface area for the glue (Loctite 380) which is good; probably more contact surface area that if you glued them to the chassis using the standard axle block feet. I used a 1.0mm plastic sheet so that the axle blocks would not be the lowest part of the chassis (I need 3/32" chassis clearance for this proxy) and a thin layer of cellophane to prevent potential glue problems.

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The result is a pretty strong unit.

That's where I am now, next up is motor and gear testing. I'll post more as I go along................assuming that all goes well..................... :pray:

Allan

[HomeRacingWorld]

Nice approach on the front blocks. Crafty :)

[btaylor]

Looks like a great Build Allan! what overall weight are you shooting for?.

Bob

[Audi1]

My target weight for most cars is 82-85g. It doesn't make for the fastest build; for that I'd want to be in the 72-76g range. But, in a proxy, the fastest car is not necessarily the easiest car to drive and, more often than not in my limited experience, the easier to drive cars usually finish higher than the "bullet car - but you have to drive it just so". We'll see. With a narrower wheelbase car and narrow front and rear tires (7.25mm width restrictions front and rear), I may shoot for a lower weight.

A lot will depend on how it does on the skid pad and the track with the different motors, gearing and tire combinations. On the track, I set my controller to medium brake and medium sensitivity, figuring that that may approximate the average of the settings that the car will encounter during the proxy. If I'm racing, I run about 85% brake and 30% sensitivity.........usually............ :D

Allan

[munter]

That looks like a winner already...I have used the PCS chassis on a couple of builds. I usually use a brass axle tube on the front, glued in at the right height.

The only thing I don't like about these chassis is the rather narrow mounting points. ie one central one at the front and two closely spaced ones at the rear.

For a minute there I thought you might be going to use the original "motor sideways offset" chassis.....no, no, no!

[Audi1]

Hi John, promise................I will not use the stock motor off-center mounting!

For mounting points, I'll be using my usual "resin" body approach with screws and plastic tube posts. I'm going to be drilling the PCS chassis in 3 places; one in the very rear; between the two holes that are there now, and two on the side pans; just behind the front wheels. I like the two in front / one in rear arrangement for posts; it gives me more support against a crash in the front and enough float to get the body freed of the drivetrain/rear wheels vibrations, which is really all that I'm looking for float to accomplish.

I forgot to mention in the last post, I usually target a front:rear weight distribution of between 35:65 and 40:60 (thank you John Kroppe (moby dick)).

Allan

[McLiams]

Allan,

Ambitious and promising looking build. That rocker panel relocation looks darned good, especially given the complexity created by the openings on the body sides. Doubtless you have realized the problem of that offset inline design.

Next year's Mercedes ROAR entry may well incorporate some of these concepts.

Mc

[dge467]

Another winner in the works? Looking good!

[Rleog]

It's always interesting to follow your custom projects.

Thanks for posting.

[Audi1]

Here's the first chassis iteration:



Slot.It white endbell motor (19.5k rpm/130g-cm torque), 10:23 gearing, 15x7 CBDesign insert wheels, XPG 22073's on the front and rear (trued, not finished), SCC front axle blocks, Scaleauto 1607 guide.........and away we go for some track testing.............

Allan

[Audi1]

Motor and gear selection made.

I ran two motors on my routed wood track today; the Slot.It white endbell that's in the pic in the post above and an H&R Hawk. I ran them both at 10V with 10:23 gearing because that's about as tame as you can get it with a 10 tooth pinion and both of these motors have plenty of torque for this skinny urethane tire / skinny body car. The results, with a chassis-only 50.3 gm set-up were:

1. Slot.It white endbell (rated 19.5k rpm/130 g-cm torque) - 7.34 sec.

2. H&R Hawk (rated 18k rpm/150 g-cm torque) - 7.52 sec.

The car is definitely faster in a straight line with the Hawk motor; in fact it "squirts" when you punch the controller. But, for overall handling, the car with the Slot.It motor is much more drivable. I was expecting the exact opposite result, figuring that the extra 1,500 rpms would overpower the car. But, in the end, I think that torque played a more important role. For comparison, in my own testing the H&R Hawk motor that I ran today is an "at spec" motor; it spins at about 18.100rpm on my tach. The Slot.It white endbell, motor is an under spec motor (18.6k rpm on the tach; somewhat unusual for a Slot.It motor.............). Perhaps that's why it seems better in the car; roughly the same tested rpm rating and less torque with the Slot.It motor (?)

Now I have my motor and gearing selection done; so it's time to re-focus on the tires and drivetrain................................

..............in the back of my mind, I'm actually thinking about a BWNC1 motor........................but I'll try to loose that thought by tomorrow morning..................

Allan

[McLiams]

Very pretty and VERY interesting...think Artie Johnson, cigarette held Continentally, pushing aside a palm frond as he turns to the camera.

Thanks for sharing your progress.

[dr fabio]

Id swap out the aluminium hub crown gear. It will never last a proxy unless you use collars to take up the thrust.

[Audi1]

[Audi1]

Got a chance this afternoon to re-locate the body post attachment points on the PCS chassis. Here's a pic the new locations with the un-trimmed posts in place:



The body looks pretty good on the posts...............maybe just a little high at this point.............(?)................................ :lol:



More next week...........

Allan