O.K I did do a archive search before posting this. I've read about problems with mechanical reverse boxes and the general consensus seems to be "avoid'em". Is there a reliable alternative? What does this electric solution look like?

gathering ideas, Fletch

I've never had a good look at one, but the general idea seems to be a starter motor of somekind driving a sprocket somewhere onto the drive train, either up near the gearbox (stuart taylor are doing this on their new race cars) or closer to the diff. All you do is put the clutch in or engage neutral and switch on the starter motor which turns the drive train the appropriate (reverse) direction. The advantage of this is it doesn't add any further mechanical stress to the drivetrain when going forward and even if it fails it won't affect the car's ability to go forwards as normal.
*I think*

Somewhere I saw where a rear disc brake had grears cut into it and the starter was engaged onto this. I'm not too sure about this method as wouldn't the starter motor be out there in the elements a bit too much?

If you are running IRS or deDion I think that it is a much more elegant solution to have a small ring gear sandwiched between the propshaft and the input to the diff. You can source a lightweight reduction gear starter and use a simple lever system to lower the starter onto the gear when reverse is desired. Rig up a push button that only activates when you are in neutral, engages a relay, presto-bingo! Reverse. The only problem with this is you will be limited to the speed of the motor/gearing ratio. If you gear it too low you will be crawilng like a slug. Too high and control could be an issue!

might have been me talking about cutting gears on a brake disc for electric reverse. But I 'm gonna put the handbrake on the prop. I aim to have a chunky mosfet PWM control for reverse - but one where you have to pull the throttle UP to make it happen - that way the engine doesn't race when you're backing up. But this is all way off in the dim distant future.......
Bob C

Here is a thread started by Bob some time ago on this subject

http://www.locostbuilders.co.uk/viewthread.php?tid=7622

Thanks for the thread help that was informative. I found a sprag clutch in McMaster Carr and have had visions of a pully fan belt arrangement between diff and prop.I'll have a second alternator if the sprag clutch ever goes out. Maddness? How much does a mechanical reverse box typically weigh? It's got to be more than a motorcycle starter and parts.

Learning, thanks, Fletch

A sprag cluth wont work, think about it / draw it out and you'll see that it would freewheel the wrong way to make you go in reverse.

I guess I'm missing why a sprag clutch wont work. If it free wheels the wrong way, is'nt mounted 180 out?( the sprag, I'm thinking, is on the starter motor).I've drawn two pulleys and a belt and it looks like it would work.What am I missing?

Dazed and confused,Fletch

Oh! I see! I may be slow,but at least I'm stupid O.K. your right about the sprag clutch. How about an air conditioner clutch?( god do i feel stupid about not seeing the sprag clutch thing)
They can handle loads of torque. Simple thing to get to work electrically. Now it would be a matter of getting the pully ratio into starter range.

Backpeddling,Fletch.

[Edited on 13/4/04 by thekafer]

Dont feel stupid, a lot of us assumed the same thing when talking about it on the BEC list, until someone pointed out the obvious!

Im not sure how an air-con clutch works tho, so couldnt comment. Any diagrams / info you can link to?

A friend of mine built a very strong / reliable system using a Subaru starter motor (cos it rotates the right way) bolted onto the side of the engine / cradle, driving a sprocket sadwiched between the prop and flange. Have a look here for some specific pics, and here for the general site which I think does have some additional info on it somewhere.

cheers

Chris

O.K., the sprocket is machined by a supplier(Blackbird) and looks like a very neat solution. Thanks for the link!


Fletch,

....hey,I know,..What if you had two sprag clutches!!???.........just kidding.

Ah yeh, now youve said that I remember where he got it now, the problem is Blackbird Motorsport no longer exist
I'll ask Ed if he knows anywhere else tho.

Chris

With reverse box prices in the stratosphere it seems like an enterprising young man would offer this as a kit. I t seems like this could be so much cheaper than a reverse box he could throw in a sprag clutch in for free!!!

Fletch.