Rob Bailey Posted August 25, 2004 Share Posted August 25, 2004 I currently have a chassis on-build for a Haybusa engined road / track Caterham - due for delivery Oct 04. They have asked if I need the mountings for a reverse box or if I am going for Hydraulic. Can anybody tell me the advantages/disadvantages of both systems? Does anybody know what kind of weight differences there is? Thanks for any help, Rob Link to comment Share on other sites More sharing options...
Violet Elizabeth Posted August 25, 2004 Share Posted August 25, 2004 Or leave it off entirely, it is just extra weight ? Of course if you are going to race then you need one. Link to comment Share on other sites More sharing options...
Irrelevant Posted August 25, 2004 Share Posted August 25, 2004 robertb: Are you using a De Dion chassis by any chance? Wrt electric/mechanical . . . .electric IMO (been reading up on it but no practical experience, still planning). If you're going DeDion, a 1 piece prop will suffice (of the right type mind you). This avoids the nasty twin prop alignment problems that plague BECs and are a feature of 99% of mechanical reverser installs. Assuming DeDion, MK Sportscars do a nice diff mounted reverser which is good as it doesn't have to transmit normal drive as the normal mechanical reversers do . .. .well until they break anyway, and at c.£800 a pop, mechanical reversers are more than MK's electric one c.£640 IIRC. Hava a look here.... Accumulating bits . . . Edited by - AdamHay on 25 Aug 2004 13:19:04 Link to comment Share on other sites More sharing options...
Violet Elizabeth Posted August 25, 2004 Share Posted August 25, 2004 Interesting thoughts on the one-piece prop Adam, even without a reverser, a 2-piece with a central bearing is the "norm". Worth thinking about how an electrical reverser works, first you have to press something to get the motor to engage with the sprocket on the driveshift/diff. Then you have to switch the motor "on". OK, so now you are going backwards, with no clutch and no way to control motor speed. Personally, if that 10-tonne truck is bearing down on me, I am going to get the hell out of the way forwards, rather than fiddle with that lot. And in non-emergency operations, I am just going to sort things out forwards. So I kind of figured out my "usage scenario" wouldn't include that much reversing. You can retro-fit electric reversers, so if it is all too much I might go for the Suart Taylor one. Not sure of the price. Link to comment Share on other sites More sharing options...
Badger Bill Posted August 25, 2004 Share Posted August 25, 2004 After over 10,000 miles of road use without one, I would say that they aren't 100% necessary. In fact, from postings on another forum, I would say that they are a downright PITA! Try pushing it for a while. If you still can't live without one, get the best that is available then. They are getting better all the time, but none are foolproof. BB Link to comment Share on other sites More sharing options...
Rob Bailey Posted August 25, 2004 Author Share Posted August 25, 2004 The chassis is de-dion tube, I assume I need a reverse of some kind for the MOT - to make it road legal. If I went for a single piece propshaft - would there not be any issues with the extra weight this put on either the diff or engine gearbox output shaft. Anybody had any practical experience with a single propshaft? Thanks again, Rob Link to comment Share on other sites More sharing options...
Violet Elizabeth Posted August 25, 2004 Share Posted August 25, 2004 I assume I need a reverse of some kind for the MOT - to make it road legal. Not at all Don't need reverse for MOT. Single propshafts are "theoretically" possible, but I don't know of anyone running one, and certainly it is not common practice among engine installers to do this. Link to comment Share on other sites More sharing options...
Irrelevant Posted August 25, 2004 Share Posted August 25, 2004 Need reverse for sprints though IIRC, even class 6 ☹️ robertb: You're in the same boat as me then. I have not found anyone else doing a DD Busa yet, and my engine hasn't even arrived yet, so I can't give any 1st hand tips. However, 2 piece props are the norm, even though they're troublesome. As long as I can get the Busa engine far enough over to have the output central, I will definately use a 1 piece prop. They can definately take it - even 3.5" steel ones should be OK. I don't see any point using 2 props as long as I can get a straight line from the output to the diff . . . .we shall see. Blackbird Cats are DD, or so someone said, but I think they have 2 piece props though - they have a central reverse box IIRC. Accumulating bits . . . Link to comment Share on other sites More sharing options...
mr_ed Posted August 25, 2004 Share Posted August 25, 2004 To run a single propshaft, of the length, and rpm, required for a BEC, the propshaft would have to be 6inches in diameter!! (Assuming it is made from mild steel). Otherwise, the torsional fluctuations will cause it to shatter. I know of only one person to try a single full length prop in a BEC, and it shattered, destroyed the transmission tunnel and made a nice scar on his leg. I believe carbon props can be made in sufficient strength to run as a single piece. This is all coz a BEC prop is about 60cm longer than a CEC prop, and a BEC prop usually rotates faster too (with a lower ratio diff to regain the topspeed). If you're mad keen on a single prop, you can mount the engine in the passenger footwell area!! Link to comment Share on other sites More sharing options...
Irrelevant Posted August 25, 2004 Share Posted August 25, 2004 mr_ed: Not according to this........unless I have misunderstood something. Assuming I'd need a 55" prop - this is quite easily catered for with 3" mild steel. Accumulating bits . . . Link to comment Share on other sites More sharing options...
mr_ed Posted August 25, 2004 Share Posted August 25, 2004 A BEC prop will typically be doing >6000rpm at 130mph. Can work it out from either your tyre size and diff ratio or engine primary reduction and gear-ratios. That site lists the critical rpm as being 4,785rpm for a 55inch prop. The critical rpm is the rpm at which it breaks, so in practice you'd want to be comfortably below this! (especially considering the high UJ angles typical in BECs) There is another interactive calculator on the DANA Spicer website. I have it in my favourites at work, will try to remember to dig it out tommorrow. Another thing, a 3inch prop is really massive! I suspect a 2inch 2 piece prop would actually be no heavier! Again, you can work this out with some simple maths. Cheers, Ed. Link to comment Share on other sites More sharing options...
Irrelevant Posted August 25, 2004 Share Posted August 25, 2004 mr_ed: I'd appreciate that link Guess I need to know how long the prop will actually need to be and how straight I can get my UJs for a definitive calculation Accumulating bits . . . Link to comment Share on other sites More sharing options...
Bare Posted August 26, 2004 Share Posted August 26, 2004 Sigh... Super7cars.com. Caterham 'Authorised' Hayabusa Caterham builders... they have a 'Bespoke' Mechanical reverser.. Beautifully made.. works as advertised. Ask em.. probably have more answers than you have questions :-). Link to comment Share on other sites More sharing options...
Violet Elizabeth Posted August 26, 2004 Share Posted August 26, 2004 It's the prop angle that is the concern, one of the reasons that I originally thought of an R1 engine is that due to it's stacked gears, the output sprocket is very central and well placed. All the critical rpm calculations are worth nothing if you actually NEED a kink in the prop to get it from engine to diff. And I would question the "troublesome" nature of 2 piece diffs with central bearing, these are being run in some RGB race series cars. Link to comment Share on other sites More sharing options...
dogvet Posted August 26, 2004 Share Posted August 26, 2004 Andy Griffiths has built a Busa Caterham it has an electric reverse, but the car is used in sprints and therefore a requirement. Link to comment Share on other sites More sharing options...
Badger Bill Posted August 26, 2004 Share Posted August 26, 2004 Guys, I'm sure that the single piece prop isn't a big issue, if a car can have one, a BEC can too. Surely the question is, is it worth the risk/effort when two piece ones work well already? Center bearings seem to do just fine, most guys sort them out, then run 'em 'til the engine needs "refreshing" 😬 14k on and I'm still on the same two piece prop/center bearing combo. And trust me, I'm not driving miss Daisy Even after I broke an engine mount and ran it without realising for 30miles (motorway, before you ask 😳) the center bearing not only kept the whole thing in check, but is as sweet as a nut after the repairs. Seems to me that people are trying to find fault with these BECs, but in fact there are a cheap way of going seriously fast. Get on ,and get installing! BB Link to comment Share on other sites More sharing options...
Peter Carmichael Posted August 26, 2004 Share Posted August 26, 2004 Badger, The BEC props are longer than the car equivalents. This gives rise to whirling problems. Link to comment Share on other sites More sharing options...
mr_ed Posted August 26, 2004 Share Posted August 26, 2004 Heres that link: http://www2.dana.com/expert/expert.htm Critical Speed Calculator. If it does nothing when you click calculate, it means that the prop you've requested is impossible/unsafe. Otherwise it asks you which series of UJs you require. Guess they are different qualities/prices etc. To get a prop with a safe speed of 6000rpm, and a length of 55inches, its looking like the prop would have to be 6inches in diameter. Thats a big mumma to have in your tunnel!! The 2piece prop with a Transit centre bearing is in use in 100s of BECs, mine included. Much better that the reverse box solution IMO. Link to comment Share on other sites More sharing options...
moomin Posted August 26, 2004 Share Posted August 26, 2004 The 2piece prop with a Transit centre bearing is in use in 100s of BECs, mine included. Much better that the reverse box solution IMO. and lighter, and more reliable, and cheaper... it's a bit of a no brainer really unless you have the balls and cash for the carbon fibre route. if you include a slider section in your prop then it should be a simple mounting exercise to add a reverse option at a later date anyway. on a related note, I currently am harbouring a K-series Caterham on my drive, it is significantly harder work to push around than my BEC. moomin www.megabird.co.uk Link to comment Share on other sites More sharing options...
Rob Bailey Posted August 26, 2004 Author Share Posted August 26, 2004 Thanks for all your replies, I spoke to Andy Griffiths last night, he uses an electric reverse and it is cheaper and lighter than a reverse box equivalent. So that is what I have gone for. Concerning the single prop shaft, because the engine does not align directly with the diff I will be using a split system - as AG. Regarding maximum stress on the prop shaft would this not be at the point of greatest acceleration rather than maximum rpm? F=ma and all that?? Link to comment Share on other sites More sharing options...
mr_ed Posted August 26, 2004 Share Posted August 26, 2004 Nope, its to do with torsional vibrations in the propshaft. The frequency of the vibrations gets higher the faster the prop rotates. Until the vibration destroys the parent material. The vibration is caused by the Universal Joints. Cos UJs are not constant velocity, like CV (!) joints. The higher the angle on the UJs, the greater the magnitude of the vibration. This is why the two yokes on the end of a prop are 90degrees out of phase with one another. The theory is that one UJ absorbs/counteracts the vibrations produced from the other one, producing a smooth final output. But the angles on the two UJs have to be perfectly equal and opposite for that to happen, and even then it doesnt seem to work well when the angles become more than about 3degrees. But as you say with a really long prop I'd imagine there'd be quite a lot of windup at max torque too! Link to comment Share on other sites More sharing options...
Rob Bailey Posted August 26, 2004 Author Share Posted August 26, 2004 I think I understand? I am a gas turbine engineer - the 2 main causes of vibration are either misalignment or inbalance in the turbine rotor. I do not understand fully how universal joints operate - Are you saying as the universal joint rotates, the balance of the rotating assembly changes. But 2 universal joints positioned at 90 degrees apart cancel out these changes? Just curious, Rob Link to comment Share on other sites More sharing options...
Mike Bees Posted August 26, 2004 Share Posted August 26, 2004 De dion BEC with (typical for BEC) 3.14 diff will have propshaft turning more slowly compared to a 3.62 or 3.92 diff ('norms' for a CEC). Mike Link to comment Share on other sites More sharing options...
mr_ed Posted August 26, 2004 Share Posted August 26, 2004 As the UJ rotates, the angle of the cross piece in the centre of it changes, and it causes small accelerations and decelerations in the rate that the shaft is rotating at. This causes torsional vibrations. Some graphs etc. here: http://www.baileymorris.co.uk/technical4.asp Link to comment Share on other sites More sharing options...
Rob Bailey Posted August 26, 2004 Author Share Posted August 26, 2004 I see the graphs make sense now. What does Bailey morris do for Caterhams? Link to comment Share on other sites More sharing options...
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