Post by David Mitcham on Oct 4, 2016 11:09:31 GMT -5
Yes they are tricky to apply! I use Micro Sol/Set when applying them prior to the last primer coat and have not had any problems either with stretching or adhesion. I think I've been successful with obliterating the lines of the decal backing but I am fairly heavy handed with the paint!
Post by Andrew Rowland on Oct 9, 2016 4:39:23 GMT -5
That's kind Peter, actually as David Mitcham has suggested to me the paint job is not Great. Actually there are two reasons for this: 1. I probably didn't sand enough in the first place and my usual practice of Sanding between undercoats and after wasnt possible due to the rivets. 2. The silver top coat is a very fine Tamiya metallic grey but it is old, dating from the Vanwall and there wasn't enough and it started to spatter at the end......
Anyway I'm not going backwards like I sometimes do!! Cheers Andi
Post by Andrew Rowland on Oct 24, 2016 1:28:30 GMT -5
A very important point has been reached....
The fixing of the stub axles has been the one single element that has always been stressing me about this build.
The differential is a fully stressed member, in the sense that I have designed it to be running on the stub axles themsleves and the stub axles then have the bearing back to the chassis via the outboard located ball races.
This was a strategy to avoid large and unslightly (6mm ID) bearings inboard and also to allow fixed suspension members back tot he chassis for strength. Inboard bearings would have meant the whole assembly having to be assembled vertically with a top screw fixing..... No good at this scale.
My approach has the draw back that the diff has to be absolutely perfectly aligned on the stub axles and I needed an adaptor to get me from 4mm to 3/32. Several people tried to turn those for me but failed to get anything like the required accuracy. In the end Maurizio machined them for me and they are perfect. I love that sound as you push to engineered pieces together and there is the faintest friction as you can feel the turned faces 'grind'.
All great but now I needed to fix the diff to the stub axles securely. I played with the idea of a split pin but that would have required a 0.8mm hole running through the aluminium, then through the hardened steel axle and then through the aluminium again, four times..... I felt that the likelihood of me getting that right first time and four times was pretty slim so I decided I should drill tap and grub screw. This also aids assembly and dissassembly a few times whilst I get everything aligned.
I tried tapping at this size a few years back on an NSR wheel hub and it came out far too loose so I was pretty nervous. I drilled at 1.5mm on the pillar drill knowing I was going in perfectly accurately and then opened it up to 1.6mm by hand. I then hand tapped from the 'back' i.e the hole I didn't want the grub screw in and this meant that by the time the tap was through the other side the thread was perfect. I have found that tapping at this scale by hand makes the end you are tapping from slightly too wide as the tap settles not perfectly concentrically.
Anyway I am happy with my result and all this means I can now simply assemble, adjust and fettle to have a running 4wd chassis.
The body? Well it just wasn't right so I sanded, added the tear drop blob at the front, sanded, sprayed, sanded and sprayed another undercoat. So now just back to the silver again. I have bought a new can and so that too is advancing well!!
Post by Andrew Rowland on Oct 28, 2016 14:55:56 GMT -5
Well finally got the chassis complete and up and running.
Goes pretty well, not sure how well yet in terms of lap times. I've been running on a dirty track and it seems to work well as it cleans the track. My fettled Lotus 72 is quicker but.... one thing is for sure it has VERY good road holding in the sense that i'm just not getting any deslots.....
Post by Andrew Rowland on Nov 8, 2016 3:10:00 GMT -5
Well it didn't turn out quite as well as I would have liked in terms of the paint job but overall I'm very proud of it. Trevor is still sitting a little too high but as yet I haven't worked out which bit of his underside needs trimming! Just some times track sessions to do to see really where it sits in terms of performance. Cheers Andi
Post by Andrew Rowland on Nov 10, 2016 14:51:05 GMT -5
So testing began last night, it wasn't what I would call a fully developed or representative test yet but I did about 50 laps with the Cosworth (CA) and 50 laps with the Policar Lotus 72 as the control. Changing every 20 laps or so as the track conditions changed.
The track was fairly dusty but not as bad as the initial chassis test a few weeks back.
Temperatires were down in my unheated hobby room. I think the air about 15 deg. C and the track maybe 12 deg. C. More about this when we talk times later.
The Cosworth is extremelly quick as you would expect with the 37,500 rpm motor and has good brakes. Again as you would expect with all those gear meshes creating drag to slow you down.
No surprises so far then.
It feels really stable, predictable, another couple of good traits. I deslotted less in is car than in any other new car I have ever driven. Not being tentative either....
There is amazing traction out of the corners, you can really get it on the power early.
Again one might predict all this so far. It acts pretty much exactly as a 4WD car would be expected to compared to 2WD.
So lap times. First the CA on the night was more consistent than the 72. Second, incredibly I got them both down to EXACTLY the same time!! Figure that. 5.41 seconds.
Now therein lies perhaps what I am predicting as the truth. The 72 was not lubricated having been unused for several months. Further the track was quite dirty so the advantage of the CA should have been quite big based on the added traction.
On my track, in perfect hot, clean track conditions that 72 has lapped as low as 4.57 which is the lap record so clearly the 72 has a lot still to give.
The CA's apart Achilles heel appears to be its desire to slide. Perhaps because all the wheels are working together at the limits of adhesion there is nothing essentially steadying it or stopping it from sliding.
It drifts through the corners and will slew out under acceleration unless the acceleration is kept well within limits.
So my guess is that although better track conditions will also help the CA, that desire to slide will ultimately mean I cannot drive it on but within the limits of the slide in order to get that lap time down. I know that on my track sliding just adds on time.
One idea did cross my mind, perhaps I need to detune the motor. Maybe my desire to overcome the extreme gear ration and the added drag of the gear mesh has resulted in my specifying a motor which is just too powerful and that something less would actually prove rather more drivable and lead to better lap times. That might work on my track where top speed is never achieved but might be different on a larger, club type track.
So that's it in a nutshell. Currently on a par with the 72 but I suspect that is a false promise.
As i'm not a great driver the utter consistency and lack of deslots of the CA is something to consider. Not losing time in deslots would help me enormously in a competitive situation.
Just to prove I was working hard, on one of only two offs for the CA I backed it hard into the barriers, breaking an exhaust off and cracking an area of the body too!! Oh well....
I need to get some more representative testing done but I hope this is interesting for those watching.
Post by David Mitcham on Nov 13, 2016 13:55:29 GMT -5
Those results are intriguing. I wonder why the Cosworth is more prone to sliding? One would think that the front wheel drive would pull the car through a corner and tend to counteract any oversteer. Are the diffs adjustable and can you change the power split front to rear? How do the tyres, wheelbase and track compare on the two cars? I wonder if trying different tyre compounds front and rear would make a difference. I take it you haven't tried it in two wheel drive mode?