Announcement

Collapse
No announcement yet.

'67 BRM P83 proxy build

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Brian, that is just gorgeous. A lovely body to complement a lovely chassis. On top of that I have seen how sweetly it runs: I would be amazed (and disappointed!) if you do not do well in the proxy.

    Extremely well done and good luck!

    Alwyn

    Comment


    • #17
      Lovely result there.

      Comment


      • #18
        Originally posted by mfogg View Post
        Oh my, that is just a beautiful thing. How did you do the driver?
        Well, it was a bit haphazard. The body and head came from bits I inherited from Keith. I'm not sure who cast them but maybe Luf or someone in the club. It was a pain getting everything to fit and look about right. I tried to paint the helmet like Spence's, which is yellow fading to an orange border around the edges.

        The chassis has one of my own innovations: a longitudinal stiffening strut between the motor and the front of the chassis. I was finding, with some of my plastic as well as scratchbuilt chassis, that the chassis would chatter while cornering. This would cause the car to scrub off a lot of speed. Stiffening the motor-to-axle connection helped in some cases but not all.

        I searched high and low for some information on this, and eventually found a couple of sources that mentioned the importance of having the right combination of longitudinal and torsional stiffness, and that low longitudinal stiffness could cause chattering in corners. So I added a stiffening strut to a few cars that chattered and it really transformed them - stopped the chattering and increased cornering speed noticeably.

        The strut runs from the top of the motor to just behind the guide flag. A straight strut will increase longitudinal stiffness significantly, with little effect on torsional stiffness. On the BRM I had to route the strut around the front body mount. The strut can therefore flex a bit, but still increases the longitudinal stiffness to positive effect.

        Comment


        • #19
          Now THERE is a slot car!

          ....really excellent. Congratulations & I am eager to see the group run.

          -Max

          Comment


          • #20
            Excellent. And thanks for the insight into the chassis tuning. It was very interesting.

            Comment


            • #21
              What wheel and tire combo are you running?

              Comment


              • #22
                Originally posted by Brumos RSR View Post
                What wheel and tire combo are you running?
                These are CB Design wheels and Paul Gage tires. The five spoke wheels look very similar to the BRM wheels, although are probably slightly large in diameter. I think they look OK though, and I like the realism of a cast wheel vs inserts. I bead blasted the wheels to reduce the shine.

                Last edited by Duke7777; 08-09-2017, 12:36 PM. Reason: added photo

                Comment


                • #23
                  Originally posted by Duke7777 View Post

                  The chassis has one of my own innovations: a longitudinal stiffening strut between the motor and the front of the chassis. I was finding, with some of my plastic as well as scratchbuilt chassis, that the chassis would chatter while cornering. This would cause the car to scrub off a lot of speed. Stiffening the motor-to-axle connection helped in some cases but not all.

                  I searched high and low for some information on this, and eventually found a couple of sources that mentioned the importance of having the right combination of longitudinal and torsional stiffness, and that low longitudinal stiffness could cause chattering in corners. So I added a stiffening strut to a few cars that chattered and it really transformed them - stopped the chattering and increased cornering speed noticeably.
                  Hi Brian, great job on both the chassis and the body!!.........it should go well

                  Finding the sweetspot on balancing both torsional and longitudinal flex certainly pays big dividends, and is the area where I believe most folks don't spend enough time experimenting. As you have found out, there is really little online in terms of explanations, so, perhaps, most folks don't have the access to the tips/knowledge.

                  In the interests of time, I will keep this short and fairly basic, but, if anyone need more details/explanations I will be happy to expand further.

                  Longitudinal stiffness......a chassis that is too soft on this plane will exhibit "axle tramp", a term coined many years ago buy the 1:1 guys, and it is simply a bouncing of the rear tires under accelerarion, caused by a too flimsy chassis. In a slot car, it can certainly be seen when accelerating through a corner, so, it can be confused with a torsionally soft chassis which also chatters through corners. As a general rule, it is hard to really make a chassis too stiff longitudinally, and stiffer is way better than too soft, so if your rules allow, most plastic, and scratchbuilt chassis will benefit from stiffening. (I should add that this mainly applies to non magnet situations......there are exceptions to the rule, namely if you are running in Europe on plastic, with only a "high leak" motor as a means of magnetic downforce).

                  Torsional flex, provides added grip by allowing the outside rear tire to progressively load in a corner, and it also creates a chassis that transitions very smoothly. The key here is controlled flex not flop, and is the reason many folks are using some sort of dampener (tape) on their previously floppy pods. The amount of flex is dependant on, track grip, corner radius, motor, gear ratio, and tire grip, with the general rule being a fast grippy track with a big motor and sticky tires requires a stiff flexing chassis, while the opposite requires a softer flexing chassis. Unfortunately there is no chart/guide to reveal the magic stiffness required, but I believe that most plastic chassis are too soft torsionally, and most of the scratchbuilt chassis I have seen in proxies or at the shop, have been too stiff.

                  After building many chassis over the years, I can now "guesstimate" what flex I will need for a particular set of rules, but, invariably, I do have to make a few adjustments, once the car is tested.

                  So....If I could offer a cheap and cheerful guide to chassis tuning........stiffen the car longitudinally, (too stiff won't hurt), build it with the parts you intend to run, and with no weight added at this time, test, and......if it chatters in corners stiffen it up torsionally, if it does not chatter, you can soften it up torsionally.

                  Bear in mind that like any specific tuning, it is very much track specific.....a single perfect set up for all tracks does not exist.

                  Again, apologies to those that found this too basic, and if anyone needs some more detailed specifics, I would be happy to reply.

                  Cheers
                  Chris Walker
                  Last edited by chrisguyw; 08-11-2017, 01:13 PM.

                  Comment


                  • #24
                    Thanks Chris - that's terrific information. I wonder why it is so difficult to find discussions about this on slot car forums? Any additional details you can offer would be greatly appreciated! Maybe we should start a new thread for this topic?

                    Alwyn and I drove the Trans-Am proxy cars yesterday on Luf's Targa track, so I knew the track would be clean afterwards. I thought I would run a few more laps with my BRM before shipping it, to see if it had any tendency to tip on a relatively grippy track. Thankfully it didn't tip, and I did a 6.58s lap. This is by far my fastest ever in any car, and definitely in "Alwyn territory". By comparison, the fastest Trans-Am car did a 6.87s in the same lane.

                    Comment


                    • #25
                      Does the guide move on what appears to be a pivot? If so, whats the advantage to that? And some ****ed fine work too, if I might add.

                      Comment


                      • #26
                        Originally posted by Tangmere222 View Post
                        Does the guide move on what appears to be a pivot? If so, whats the advantage to that? And some ****ed fine work too, if I might add.
                        No pivot - the guide tongue is soldered solidly to the lower front cross member. In one of the later photos you can see some small wedges I soldered to the sides of the guide tongue, because the guide was rotating too far. In the earlier photos you can see a small hole in the top of the guide tongue - this is to anchor the front end of the longitudinal stiffening strut you see in the later photos. I just use hot glue to keep the ends of the strut in place, and this blob obscures things somewhat around the front end of the strut.

                        Comment

                        Working...
                        X