From: M.S.Gerritsen@sms.utwente.nl Date: Tue, 8 Dec 92 15:39:25 WET Subject: stub-axle brakes Has anyone experience with or know of braked, side-mounted hubs, eg as used in three-wheeled 'redundants'? /Marten From: Dave Garnett Date: Tue, 08 Dec 92 16:56:12 +0000 Subject: Re: stub-axle brakes >>Has anyone experience with or know of braked, side-mounted hubs, eg as used in >>three-wheeled 'redundants'? I have recently completed building a Windcheetah (Mike Burrows design) trike, which has stub axles all round. The front wheels are based on modified Sachs hub brake units. The mods involve replacing the bearings with sealed ball races, making a new backplate and stub axle. They certainly work as brakes, and I've had no problems with the stub axles themselves. If there is going to be a problem with this sort of design, it will, I suspect, lie in the (long term) sensitivity to fatigue/impact cracking. However, I observe that most cars are built like this, and wheels don't often fall off ! Incidentally, I endorse what has been said about Magura brakes. My Peer Gynt has them, and I'm very impressed, although I have had one incident with a punctured brake pipe. regards, Dave From: mason@asylum.sf.ca.us (Latte' Jed) Date: Tue, 8 Dec 92 17:07:54 -0500 (EST) Subject: Re: stub-axle brakes I spent literally years dicking with this before I found a workable solution. There might be some easier way, but I never found it. I'll skip all of the things I tried that failed. The solution was able to handle me (190lbs) and my 220lb roomate doing jumps over the sand traps at a local golf course (yes I know this is sociopathic) I used a plain old atom drum brake hub. I banged the races (steel inserts) out of the hub and got two 10mm ID 30mm OD sealed cartridge bearings from the local bearing shop (atlantic tracy in somervile, mass). The inside of the hub (where there used to be a race) isn't 30mm, but it's some english size that's just a bit smaller. If you like you can machine it, sand it, whatever, it'll make your life easier. The two bearings can be pressed in just like replacing normal sealed bearings - set the bearings in place, stick an axle through, put a washer and a nut on each end so the nuts press the outside race of the bearing only, then torque the sh*t out of it - assuming you didn't machine the hub to 29.995mm. Make sure the bearings go in straight, which is tough if you didn't machine the hubs. Go the the local hardware supplier - it'll probably have to be an whosaler, hardware stores don't carry this sort of stuff. I went to Stuart Fastener, again in somerville, mass, in the same building in Special Purpose Vehicles. Get a 10mm hardened shoulder bolt, this will have a 10mm shaft that will go all the way through the hub and threads on only the last half inch or so. You'll probably have to weld this onto whatever it'll be mounted to, I tried to bolt the axle on but never got it really tight. On the brake plate, the part that has the shoes on it, there's a U shaped thingie sticking out that's meant to fit on a notch on the frame to keep the backplate from spinning. File, machine, grind, &c. this thing off and drill a 9/16ths (or thereabouts) hole, get a low-profile-head bold (or grind a normal bolt head down) and bolt it to whatever the axle's fixed to. Put some appropriate number of spacer washers on the axle to space the spinning part of the hub out so it doesn't rub the backplate. Put the hub on, a nut and a locknut, and drive away! Easy, eh? Assuming you've got two wheels on the front or back (hopefully the front) of a trike (or maybe a quike) and not a one sided fork you'll want to have one brake lever controlling two brakes. There are levers made that do this. Or, if you're really sick, you can modify a magura hydraulic to operate both brake arms, but that operation's too traumatic for me to discuss. I used this hub setup on a two/front one/rear mountain trike with 20" fat wheels all around, I use it in the woods in the summer and on ice in the winter, the only thing that's ever bent one of these axles is slamming a curb sideways at about 20mph. It takes jumps, riding on two wheels and 360 degree skids on asphalt without a complaint, though I do spend a lot of time trueing the wheels. Two drums in front offers all the stopping power you'll ever need, although there is the risk of tipping the machine up on the front wheels. My trike has a *very* low CG (3" ground clearance with a helluva skid plate) and I can still tip it up if I put my weight on the pedals. From: Dave Garnett Date: Wed, 09 Dec 92 15:32:30 +0000 Subject: Re: stub-axle brakes Re modifying and assembling hubs, I will observe that modern anaerobic adhesives are excellent for fixing things like bearings in place, and will tolerate quite large gaps. I have used Loctite 638 with excellent results. You must de-grease properly, but otherwise it couldn't be simpler, and you can always dis-assemble (by heating to > 150 C) if you need to ! I would be very wary of welding a stub axle in place, as you are almost certain to get a heat affected zone with poor mechanical properties. It is better in my opinion to screw (and glue using Loctite or similar) the axle into a suitable lump of metal (aluminium casting in my case). I would also go for the largest diameter I could get in. You will probably find that you can get bearings with 12mm (near 1/2 inch) bore that will fit your hub. I don't believe that 10mm has much strength reserve ! regards, Dave Garnett. From: mason@asylum.sf.ca.us (Latte' Jed) Date: Wed, 9 Dec 92 23:05:21 -0500 (EST) Subject: Re: stub-axle brakes The loctite would have no problems holding the bearings, except that as the hub and bearing come they're a tight fit. I've never had to replace the bearings, but if I did I'm sure I'd find they're too tight a fit. I was surprised how well loctite holds up to pounding. I had a headset race that had come loose and banged the frame out of shape, a few drops of loctite and it took probably 20K miles (then it was written off under a car). Welding the stub axle on does make replacement difficult, but I couldn't find any method that would hold it otherwise. Most motorized vehicles use stub axles with a taper fit to the kingpin ass'y, but I couldn't find any pre-made axles in appropriate sizes. I checked units made for go-karts and similiar light weight applications and they were still too heavy and inconvenient sizes. I had no problems with the metal being weakened by the heat, my "kingpin assembly", (does it have a better name?) was made of ~1/8" mild steel, folded to a box section and brazed. It's never bent and is a practical weight. If I had used a much thicker lump of metal to bolt the axle to (1/3" - 1/2"?) I probably would have had a better chance of it holding. What's the alumium casting you're fixing the axle to? Sounds like something more high-tech that what I came up with. I was hesitant of the 10mm axles at first too, but I tried them at the suggestion of a friend who races formula karts at often over 140mph and 3 lateral G's (really!) on axles made of 10mm shoulder bolts. I considered switching to 12mm axles but a check of the major bearing manufacturers (the bearings I used were fafnirs) showed that I'd have to switch to a more fragile more expensive smaller ball unit. I really didn't expect the 10mm axles to hold up, but I've showed no mercy, and it's held up well to any kind of abuse I've figured out how to dish out. Hitting a curb at high speed sideways did made cheese doodles of one axle, but that's the kind of thing I try to avoid (:-). From: M.S.Gerritsen@sms.utwente.nl Date: Fri, 11 Dec 92 12:28:54 WET Subject: stub-axles Thanks for the info. I haven't done much calculation, but I would guess that a stiffer 12 mm axle with bearings with a reduced load bearing capacity ( as opposed to a 10 mm ins dia bearing) would have a longer bearing life. Wheel diameter plays an important part in stress-calculations for an axle. How do carts reach 3G's?. They have aerodynamic downforce? With those tiny wheels, the side and downforce moments will (roughly) even out. The highest stress could occur on the long straights. (that was where in the early days of aerodynamic auto racing wheels collapsed). With carts, driver fatigue is probably more important for part life than metal fatigue. Wheelchairs come with 1/2" pip-pins If I would have to design my own axle, I would probably glue or pressfit a 12 mm inhexbolt in a tube, and use a anti-compression spacer between the bearings in the hub. /Marten