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how stong are BEC diffs
Mr Whippy - 10/4/08 at 09:58 AM

Ok rather a vague crappy question I know but how strong are these chain drive diffs used on some of the BEC cars? (no I'm not going BEC I can assure you) would they for example handle the weight of a saloon car day to day without falling too pieces? Not thinking of masses of power going through it rather just a high torque most of the time.

Paul TigerB6 - 10/4/08 at 10:03 AM

We know you really want bits of a BEC in your car but why would you want to put an alternative diff into an everyday saloon car??

Mr Whippy - 10/4/08 at 10:15 AM

just pricing stuff out for a project and working out the most suitable parts to use

Miks15 - 10/4/08 at 10:18 AM

arent some of the chain drive diffs just modified car diffs?

Paul TigerB6 - 10/4/08 at 10:20 AM

I would think the weakest link will be the chain myself rather than the diff. I guess a double chain might be an option using two sprockets bolted to the diff / gearbox output???

Mr Whippy - 10/4/08 at 10:37 AM

quote:
Originally posted by Miks15
aren’t some of the chain drive diffs just modified car diffs?


They are? I thought the whole casing turned on the BEC diffs so that only leaves the planetary gears that could be used. I need to check that up.

Two chains is a good idea, plus I was thinking of fabricating an enclosure to keep it clean. This is the kind of diff I was thinking of using -

[Edited on 10/4/08 by Mr Whippy] Rescued attachment diff.jpg
Rescued attachment diff.jpg

greggers - 10/4/08 at 10:46 AM

Is this for your electric car idea by any chance?

smart51 - 10/4/08 at 10:47 AM

The Sylva R1ot uses a fiesta diff, without the casing. The chain wheel bolts to where the crown wheel used to go.

Mr Whippy - 10/4/08 at 11:02 AM

quote:
Originally posted by greggers
Is this for your electric car idea by any chance?


Yeah that’s right. I figured that if I did away with the engine, gearbox, exhaust, fuel tank & radiator, most of the weight of the batteries would be compensated for. Sounds like using a motor through an auto box is a problem due to the need to maintain oil pressure in it even when stationary so I was just going to make it direct drive though I have a good manual box in reserve and a new manual steering rack. Just rather do away with the 40kg of the box altogether...

I only ever use the car for short journeys around town – work, shops etc. Mostly sitting in traffic, so range and top speed are irrelevant, I have the Volvo for long distance anyway. The cars getting fully done up right now so thought this was the ideal time to convert it. I was going to use water cooling for the motor to heat the demister.

[Edited on 10/4/08 by Mr Whippy]

PAUL FISHER - 10/4/08 at 11:18 AM

The sprint R users the fiesta diff internals

MikeCapon - 10/4/08 at 11:29 AM

If you want to uprate a chain drive, use a duplex chain.

I had found you a lovely piccy but for some reason I cant upload it.

Look for "duplex chain" in Google images.

Edit to add image


Image deleted by owner

[Edited on 10/4/08 by MikeCapon]

Miks15 - 10/4/08 at 11:34 AM

Mr Whippy - 10/4/08 at 11:37 AM

certainly looks the way to go cheers

trikerneil - 10/4/08 at 11:57 AM

I know of a Hyabusa Trike (claimed 178hp) with a single chain driven Reliant Robin axle.
It's been on the road for about four years now with no problems, and the owner rides it like he stole it!

I think the crownwheel and pinion are the weakest link in a normal setup.

Neil

russbost - 10/4/08 at 01:13 PM

All the chain drive diffs apart from really specialist (& expensive) stuff use car diffs. I would agree that if there was a weak point it would be the chain, but if you can transmit 'Busa power usedas it is in something like Z cars Mini without a problem I really don't think you're going to have a problem with an electric motor. The biggets loading on a diff is when you rev up (particularly with a big heavy car flywheel) & dump the clutch - I can't imagine a similar situation with an electric motor.
You will also be saving most of the weight of a big cast casing - the sideplates on chain diffs don't weigh much.

Mr Whippy - 10/4/08 at 01:43 PM

Russ,

What did you uses on the Furor? you put quite a bit off power through it with the two engines. Do you have a linky?
Like you say the initial starting torque really isn't going to be very high especially without using a gearbox, I think the motors peak torque is around 4000rpm but I'm not after a speed machine so don't care about 0-60 times.

[Edited on 10/4/08 by Mr Whippy]

matt_claydon - 10/4/08 at 04:43 PM

Peak torque on a motor (unless there's some kind of controller interfering) is at zero rpm.

jono_misfit - 10/4/08 at 07:06 PM

My friends most recent hillclimb cars put nearly 400 Bhp and 300nm of torque through a fiesta diff. They havent melted yet, but then again its probably done less than a hundred miles.

russbost - 12/4/08 at 12:06 PM

On the Furore - the existing car that is - it doesn't have a diff, each engine drives each rear wheel separately so power is split between the 2 drives - around 137BHP & 80 or so Nm torque each.
I'm sure you'd have no problem with any normal chain drive bike diff.