Post by David Mitcham on Mar 30, 2016 15:06:57 GMT -5
This is my1.5l class, VRAA 2016 entry. The 1961 US GP was Tony Brooks last race; he finished third from tenth at the start. Tony was an underrated driver in my view and probably retired too early. He became frustrated in 1961 with the 'gutless' 1.5l cars and, as he saw it, their inability to 'separate the men from the boys in driving terms'. BRM were was using the underpowered, 1.5l Coventry Climax four cylinder pending the V8 used in 1962.
I'm using the shell based on my carving of the P48/57 and cast in resin by the redoubtable John Warren. The body has been opened out and a simple chassis constructed using Richard Mack steel front and rear brackets. The chassis is probably Mk1 as I want to try something a bit different; I thought I had better have something for testing purposes and for comparison with the P578 from last year's VRAA.
Post by David Mitcham on Apr 27, 2016 15:52:11 GMT -5
Apologies for the lack of progress reporting. I now have two different chassis for the BRM. One is the conventional construction I posted above and now a Policar based one – motor/gearbox pod rear end and brass front. I’ve more or less decided to go with the Policar/brass hybrid on the basis of some timed tests and its general feel/drivability. Incidentally I’ve fitted a 5 degree angled, 11t pinion. On my track I’m not convinced this is better than the standard Policar gearing but given the overwhelming advice on what’s needed for the VRAA (and my salutary experience of last year!) I’ll stick with the 11t pinion.
Having decided on the chassis I started building the rear suspension. This raised two fundamental problems: how to attach it to the pod; and how to make it removable should attention be required to the gearbox. After trying a number of different approaches I settled on making a casing (screwed to the underside of the pod) out of thin tin sheet, fitted round the lower part of rear of the pod, to which I’ve soldered the lower and upper A arms. These are attached to the uprights using the radius rods for the lower ones and wire pins for the upper ones thus the uprights can be detached allowing the whole assembly to be removed from the pod – well that’s the theory! At the moment the springs and the anti-roll bar are completely lose until I decide where to attach them permanently – although as its turned out the body holds them neatly in place.
On to the front suspension next and then a serious attack on the body!
I’ll let the pictures below explain things in more detail.
(Note the apparently large diameter axle is because there are aluminium spacers between the uprights and the pod axle bearings - they are there to make sure all is square and the correct track is achieved. They will be removed!)
Post by Andrew Rowland on Apr 28, 2016 1:39:55 GMT -5
That is going to make a wonderful model David. The rear suspension looks even better with the body on! Interesting to hear about your test results too. I wonder what will happen during the series?
Do you think having the outrigged bushings is causing slightly more drag on the rear axle than is necessary? I wonder if you might consider reaming them out slightly so as the axle does not touch them?
I put some Paul Gage tyres on my Lotus 21 last night and it has transformed the handling. Now I know why my car was such a handful on the Scaley Cooper rubber.....
Looking forward to the series although I must remember to pay before the deadline!
Looking good David. I love the idea and design behind the keeping of Andi's wonderful and clever pod separate. Your suspension detail is superb! It looks as if it might actually work with the body on. IMHO I would have thought the bantom weight VRAA spec motor would be at a disadvantaged with the extra coefficients going on in the drive train to try and keep up with the gear ratios common to conventional gears for VRAA. You hinted at not being convinced compared to the regular Policar gearing. Why? In relation to VRAA the advise on gear ratios you've been given is relevant to gearing using 1 pinion and 1 crown. Not being critical its just an observation. I love watching your builds come to life, this is another brilliant concept and build. What is the 5 degree pinion your using and how many teeth does gear on the axle have?
Post by David Mitcham on Apr 30, 2016 10:28:30 GMT -5
Thanks for the compliments! Most of my ideas come from seeing how you and others build you cars.
I'm sure you're right about the extra friction in the Policar gearbox. However I have tested the chassis against the conventional one I made for the BRM and against last year's VRAA car - and against the Policar Lotus 72 and the Policar chassis for the Ferrari 312 I'm building. I think, and the times over 10 laps showed, that the frictional losses in the Policar drive train are more than made up by smoother, more controllable, drivability. The BRM was third quickest after the two standard Policars which is what I expected given the longer wheelbase, wider track and wider tyres of the 72 and 312. Time will tell if the BRM is competitive in the maelstrom of the VRAA - I suppose my main reason for going the Policar route is to try something different.
The spur gear on the axle is 16t so the pinion ratio to crown is the actual gear ratio (11:25 or 9:25 in standard set up). The angled pinion is made by ARP and I got mine from SCD (the redoubtable Chas Keeling) in the UK.
Hi David The ARP Pinion looks interesting, not seen the slight taper on a pinion before. Is it designed for infinite gear mesh backlash adjustment? The idler gear is 25/16, a reduction of 64%, From what I have seen the final Ratio of the Highest geared VRAA Cars is 2.3:1 with up to 2.6 being common. You are running 2.27:1 with this set up. Using the 17 tooth gear on the axle would give 2.41:1 and using the 18 tooth would give 2.56:1 using the 11 pinion. I'll have to get one of Andi's pods, they look to be a trick bit of kit. Keep up the good work it is a very interesting build. Looking forward to see how you tackle the front suspension detail.
Im running Dan Gurneys' BT7 of the 64' French GP, #22. It will be, most likely, a more traditional chassis using my brass angle bracket and guide tongue and piano wire without the floating pod and the outboard rear bearings using silver bearing solder with only suspension detail being silver brazed. Not decided yet but thats what Im thinking.
Post by David Mitcham on May 28, 2016 14:33:39 GMT -5
The front suspension is now partially complete - springs, stirring arms and anti-roll bar to go! I've spent a lot of time trying different ways of constructing it - particularly the lower A arms - and its a combination of nickel silver tube and rod, brass strip and aluminium for the uprights/hubs. I'm also on the third chassis iteration using one of Andi's universal front ends for the Policar motor pod. Its light and seems quick and consistent so its what I've settled on. Incidentally the rear suspension shown in previous posts has been removed temporarily.
Post by David Mitcham on Jun 6, 2016 15:03:24 GMT -5
I seem to be on a bit of a roll at the moment so here is the latest on the P38/57. All the chassis detail is now completed; the body is primed; Tony Brooks is being painted; the wheel inserts are primed and may get a top coat of Halfords' aluminium tomorrow; the mirrors, exhaust and screen have been trial fitted.
Eye candy David! Is the front assembly floating? Your design makes it look possible to allow the front ride height to be adjustable. I'm really looking forward to the driving impressions of this car compared with standard setups. The "smoother, more controllable, drive-ability" characteristics sounds especially intriguing. Why does that happen? Does the extra gear smooth out the mechanical impulse imparted to the tires?
Post by David Mitcham on Jun 7, 2016 13:17:45 GMT -5
Thanks for the complements. Andi's universal front end might allow adjustable ride height but I haven't built it that way. I'm really not sure why the Policar 'gear box' makes for smooth controllable set up. I think its, at least partly, because its really well engineered and fits together precisely. I've built three chassis using the Policar components and they all run in the same smooth way (as does the Lotus 72 straight out of the box). I also think you're on the right track regarding the extra spur gear. Maybe Andi can explain it to us from an engineering point of view!
Post by Andrew Rowland on Jun 8, 2016 1:45:34 GMT -5
I'm not 100% sure 'why'. The original thinking that led me to this solution was about braking for high revving, low torque motors.
The theory was that in an old clock the heavy weight makes the tiny hands turn slowly but turning the hands cannot pull up the weight! So the motor can turn the rear wheels very easily but the rear wheels find it more difficult to turn the pinion. Now I am not really an engineer so maybe that is not correct (there are other things going on in old clocks), but that was the oriignal theory.
It is what I call a mechanical 'disadvantage'. I think some people believe it is just extra frictional forces but I would maintain that It is more complex than that. If it were that then you would expect the cars to be slower NOT faster than other cars.
For me, a poor driver, I lose all my time in the corners where I cannot balance the power so I wanted something that is very forgiving and driveable. Early on I went down the route of ever more power but no matter how much faster I got down the straight I was so slow in the corners everyeone passed me. I realised that real cars are the same so started looking at how to create the braking effect.
That ability to brake seems to not have a negative effect on acceleration with 25K motors but it will be very interesting to see what happens at the VRAA. Both David and I are dreaming of a mid field position but that's a secret......
David, your BRM build is absolutely amazing! I don't know how you managed to solder the front and rear suspension bits without melting the Policar composite chassis parts. And how do you fabricate those uprights? I have spent many minutes studying the photos of your handiwork hoping for enlightenment and inspiration. Unfortunately, to date it has only fed my "builder's block" and my two entries remain unstarted on the work bench. I'll go down to the basement workshop again this evening to look at the body shells and other raw materials. Perhaps tonight I will make a start....