Joined: Mar 2008
2WD design thoughts [First post update: RESTORED]
EDIT: I wrote this out once and then had some unpleasantness following so I deleted most of it. Seems it needs to be written up again to correct some errors and try to explain better and more fully. At the same time let me add that if folks couldn’t understand it the first time that it dawned on me that maybe it was written for crap and wasn’t clearly understandable! I didn’t want to take up miles of bandwidth the first time but maybe it was abbreviated too much.
So because I posted it up in the first place I’m going to assume all blame for any difficulty understanding it and apologize for losing my temper over some of the replies. Claude Stanley mentioned that he personally knew a couple of posters who replied, that they’re good people and he doubted they meant to be directly offensive, or if so they were just having a bad day. Good enough for me. Without further ado:
I’m working on building an outfit in the near future and have given a lot of thought to 2WD. I hear a bunch of negatives and complications, but most all say the traction is great if it works so it sounds good to me. Possibly this planned design would be of use to others contemplating 2WD. This has been tested with some very high loads and extremes of applied horsepower but not in a sidecar rig.
It is my own original design not based on any other Limited Slip drive system or differential I’m aware of. I’ve worked and searched around the automotive, truck, bike, kart, race etc. scene for 50 years while looking for a Limited Slip like this and never heard of it yet so I went ahead and designed it myself. It isn’t stolen from another application or anyone else’s design that I’ve ever heard of but it is based on a simple clutch and driven plate, underlining simple.
I have a complete bike rear wheel/sprocket/brake for my hack with bike's original swingarm and shocks. This build will have a PTO at engine. Come off the PTO with a u-joint [maybe not necessary] to a driveshaft with splined connection and spring loaded clutch assembly and across under the chair with a driveshaft. Chain drive from driveshaft to sidecar rear wheel.
For the PTO come off the engine’s countershaft output sprocket to another sprocket on a jackshaft, with jackshaft of course mounted in bearings. 1st jackshaft sprocket spins shaft and powers the PTO power takeoff at other end. Add another sprocket next to the first on jackshaft, this aligned with a sprocket on a lay shaft mounted in bearings behind it, in front of rear wheel. Add another sprocket to lay shaft, this aligned with bike’s rear wheel sprocket and original countershaft sprocket and normal drive system is restored plus you now have the jackshaft PTO.
PTO & layshaft mountings may be simple plates, possibly in a boxed configuration and aluminum should suffice, or plates may be suspended between a few new, small diameter tubes added to frame with shafts in quality roller or thrust bearings as needed.
In order to make system usable in full-time 2WD: a driveshaft is mounted to PTO, possibly by u-joint, with driveshaft split in two. Choice of keyed or splines for mounting u-joint if used on jackshaft. U-joint may not be needed depending on configuration. Mount drive shafts in bearing supports under chair with flanged thrust bearings and thrust collars/washers as needed.
Jackshaft PTO end on chair side should be in a thrust bearing with mounting acting as thrust plate with suitable thrust washer/collar as needed, to withstand force applied by driveshaft. Proper high quality thrust bearings, thrust collars/washers are critical here where non-thrust bearings would be shredded in short order and could possibly lock up bike or chair wheel!
On the two adjoining ends of cut driveshafts attach hubs/plates facing each other. One plate gets clutch-type friction material and the other may be a steel plate, or friction material on both. There are shops that rebuild clutches so it shouldn’t be hard or expensive to get a custom hub/plate faced with friction material, or else do it yourself. One steel plate is better so that only one friction material needs replacing in the future.
These hub/plates press against each other face to face, carrying power from jackshaft PTO across under chair through driveshafts to a sprocket on far end to drive chair wheel. Driveshaft should be mounted in thust bearings with thrust collar on shaft as needed. Mount it all up so that it's adjustable for spring pressure between the 2 shaft ends with hub/plates and friction material if desired.
One driveshaft end may be splined with that shaft’s clutch hub/plate internally splined and then spring-loaded. A coil spring over outside of shaft from a shaft mounted thrust collar to clutch hub applies constant spring pressure to clutch plate against adjoining steel plate on the other shaft as needed, but with options on spring ratings. A thrust collar is required on shaft for spring to press against to maintain pressure on splined hub/plate and multiple springs might be used. A second spring over outside of first might be engaged with an adjustable thrust collar when 100% lockup is required, disengaged for normal riding.
Clutch hubs and plates may be mounted in the open space between tug and chair for the sake of ground clearance. Note: mounting for driveshafts with clutch assembly may be made adjustable for a quick increase or decrease of spring pressure. Also it may be possible to eliminate u-joint and second driveshaft and simply run a steel hub/plate directly on jackshaft end and friction hub/plate on single driven shaft end carrying power to sidecar wheel sprocket, obviously the simplest setup.
The only outside-sourced machining operation required is to have shafts and hub splined, however there are sources for custom splined shafts. Nothing huge needed, just enough to handle your bike engine’s horsepower. Not that difficult to make your own hubs and plates and some will have leftover machine parts that will do nicely for all needed parts with a little modification.
Some were dubious that a single small clutch/driven plate of 5”-6” diameter could withstand pressures and power applied in this way. Same system is used successfully with 800-900, even 1,000+ HP applied to a single 12”-13” clutch plate/driven plate in countless drag racing applications. In street machines countless more vehicles running 200-700 HP with single 10”-12” clutch and driven plates for about 50,000 miles before even changing clutch frictions in normal use. Even the extreme torque of large diesel-powered trucks is handled by a single 12”-13” clutch plate for many thousands of trouble free miles. It works, use whatever clutch/driven plate size you think necessary.
With this setup I can adjust by spring pressure and bearing mounts to have full traction or less, like about 50% of full engine power on hack wheel, give or take. This allows light enough pre-load so that sidecar axle and wheel can slip as needed in turns on hard surfaces, either speeding up or slowing down, but as if free-wheeling.
Of course I'd expect some clutch plate wear over time, maybe not all that much. It would be quite similar to the continuous slip seen 4-5-6 times at every stop light or stop sign in an automotive manual transmission system but here with less applied horsepower, far less mass or weight to move and much less slip than that overall. This slip allows the 2WD to function as a Limited Slip differential where the driveshaft sections are similar to the axles in an L/S setup.
This setup would give a whole lot more extra power on soft surfaces and leave everything drivable on hard surfaces with axle/wheel speed differentiation as needed. For my own use it will not see extreme offroad but still planning to lightly enclose clutching assembly so a bunch of trash and guck doesn’t foul it. Something like a light gauge aluminum box to keep things fairly dry and clean.
I hope that explains things better and that some folks can get some good use out of this. There's a further possibility written in between the lines but I'll leave it to you all to discover it. I still can’t get it written to be perfectly understandable to all but hopefully this is better. I have no lasting grudge or animosity against anyone here and afterall, it is the Christ-mas season, eh? Have fun!
XL-erate screwed with this post 12-16-2012 at 06:40 PM