Run a pumpkin in reverse?

[davesax36]

What would happen if I ran my final drive in reverse? I mean is it possible for the ring gear to push on that worm gear without destroying it? I'm trying to figure out how to put a vmax engine in a locost 7 build and I had this idea for getting the output to spin in the right direction for a normal automotive rear diff.

Don't kill me, I'm really trying to figure this out without having to build some sort of offset parallel shaft gearbox and use a cv axle to compensate for whatever driveline angle problems I still might (will) have.

Thanks, guys.

 

[one2dmax]

I am not sure what our Vmax final drives would do in reverse? I know there are some Honda's that can run in either direction but not sure if they are straight cut or helicals (like the Vmax).

 

[Fire-medic]

I recall reading a story on Ed Roth running a Corvair transaxle upside-down for one of his car designs.

 

[davesax36]

I'm mostly trying to figure out if the ring gear driving the worm in reverse would work. Even if it wears things more quickly, I think it could be ok for a lot of miles before things went wrong. Trying it by building a shaft that has wheel splines attached to both ends is step one either way. I'll see how far I get into this before I give up or use a more common engine solution (busa, R1, Gixxer 1k).

 

[02GF74]

Not entirely what you are planning to do so I may have misunderstood your intentions.

A locost 7 is RWD with an engine in the front.

Assuming you intend to mount it longitudinally, then you need a long propshaft to take power to an axle with a diff at the rear, so you don't need the final drive part.

Problem is if you want the engine central, then you either need to move the transmission tunnel to the left (a major task) else use UJs to turn a fixed propshaft in the tunnel.

Bike engined locost have the engine mounted transversely, the shaft on which the drive sprocket is fitted to would drive the propshaft.

Can you possibly post a diagram of what you are planning to do.

There may be useful information here(I haven't read it all)

http://www.locostbuilders.co.uk/viewthread.php?tid=172732
BTW definitely worth joining that forum if you intend on pursuing this project.

 

[davesax36]

I would center the engine, which means the output shaft would be offset to the left. It also turns the wrong way for a normal automotive rear diff. Unless I'm nuts and the output shaft rotates counterclockwise, I need to drive the second pumpkin in reverse to give the proper rotation to whatever driveshaft I go with. This will be a Gen1 motor so I can use pod filters to keep the height down. If it really isn't going to work, I'll probably look for a wrecked R1 or (even better) busa to pull the motor and electrics from. Then it's easier to just center the output shaft and use a splined adapter to turn a driveshaft.

Here's a crappy overhead view with a misshapen vmax engine, two pumpkins, and a normal rear diff.

 

[MaxMidnight]

From your diagram you are using two are using two final drives and a differential?

The main problem, if I'm understanding correctly, is that each final drive will reduce the output speed of the motor by a ratio of 2.851:1.
The second final drive will reduce this again by the same amount and finally the differential would reduce it again.
Assuming all reduce at the same amount at 5000 rpm the rear wheel would be turning at 290 rpm.
I don't know what tyres you will have but a 175/65 R16 takes 809 revolution to do a mile and on that basis you would travel less than 0.4 of a mile in a minute or at at speed of 24 mph. (please feel free to correct me if my math or assumptions are completely wrong!)

 

[Parminio]

Third edit. Why not an offset differential?

 

[02GF74]

The picture makes it clear what you are trying to do.

As I say, everything's possible given enough time and money.

I expect a Vmax engine is cheaper than one from a Hyabusa but due to the offset drive, the Vmax is somewhat problematic hence there's probably few or even zero cars with one.

You can can be a trailblazer and be one of the few or follow the herd and fit 4 cylinder in-line engine.

@midnightmax, the second final drive is being driven in reverse so negates the final drive reduction.

If I were looking at doing this, I'd look at fitting a gear on the engine to drive a second gear to which bolts the propshaft.

The number of teeth on the two gears will allow fine tuning of the final drive, and allow a greater variety of axles to be used.

The second gear reverses propshaft rotation.

Apparently there are honda engines that spin the opposite direction so the diff in the rear axle reverses rotation and would allow using two sprockets driven by a chain, which would make it easier /cheaper.

The question is can a gear or sprocket be attached to the Vmax engine and be strong enough to keep the gears/sprockets in position.

 

[MaxMidnight]

@midnightmax, the second final drive is being driven in reverse so negates the final drive reduction.

Ah yes, thanks for pointing that out. However, unless you have a differential that operates 1:1 that would also lower the gearing.

If you wanted to keep 1:1 as far as the diff then using three middle gears would do it but add additional weight and complexity.
IMO an offset driveshaft would be a neater

 

[Screwloose]

Third edit. Why not an offset differential?

View attachment 81494

I’ve seen trikes here with offset diff’s. I think they get them out of old Robin Reliant's, but I’m guessing at that one.

Also the less intermediate units used, the less power losses through heat I would imagine.

 

[davesax36]

Pumpkin one goes 3.66:1, pumpkin two goes 1:3.66 -- Netting 1:1 output. I really need to just put an adapter driving a single sprocket that uses a chain to turn another sprocket which turns a gear on a shaft meshed with another gear before output to reverse the drive direction. Change gears inside small transfer case box would be from a Winters quick-change rear end. Actual final drive ratio in the rear diff would probably be 4:1 to account for car vs bike tire diameter.

Offset diff makes it tricky to have two seats in a vehicle this small. All the Honda B motors were front drive as far as I know, so they didn't need to convert anything for drive direction. It was all done in the transmission. Using just a chain to drive another gear makes everything spin in the same direction, which is why I need to "build" this reversing box. I'm not even really interested in a forward-neutral-reverse box since I'll have another solution for reverse with a starter motor and gear from something else bolted at the rear diff.

 

[02GF74]

Any progress on this?