The Hodaka Club Forum

I went to the garage to run a quick prototyping test. I clamped a 1/4 diameter steel rod in my bench vise with 2" of rod sticking up above the vise jaws. Then I clamped a ViseGrip to the upper end of the rod - leaving slightly less than 1.75" of "free length" between ViseGrip and vise. I then hooked the end joint of my pinky finger on my left hand onto the ViseGrip and easily pulled approximately 3/8" torsional rotation into the rod. So we have 1-pinky finger of force on about a 9" lever arm with 3/8" of torsional "wind up" in the rod (measured at the end of the ViseGrip). If my fishing scale hadn't expired, I could give you a real force measurement. Ennnneywayeeeee, I still think the 1/4" rod is wayeeee undersized. Your mileage may vary.

Ed

Ah, a fun and satisfying day in the Hodaka shop. A leisurely pace of design and manufacturing eventually ate up the whole day. First the building of the pivot levers which you must remember was done with a drill press, hack saw, bench grinder and associated files etc. Big fun. A test assembly to check clearances which I somewhat got through. My, some of this is really close . It all fits and I still have some options with jam nuts and shortening some bolts. The 1/4 inch shaft is looking a bit wimpy and I'll probably go with Jack's idea of a tube between the two levers. We can get a few more welds with that set-up for strength and it will be an accurate spacer for a some what critical measurement between the levers. Luckily the angle between the two levers turned out to be 180 degrees which simplifies things.

I mentioned earlier that I had some problems threading the aluminum shaft as the die kept cogging and wandering. I did use oil on the die and shaft and one would think that oil is oil and motor oil would do. Today I bought some Thread cutting oil (Ace Hardware of course) and things went much better. Quite the difference. All went well.

Here's a couple of shots of today's progress. A tube spacer and welding and all should work!

Maxie

Hey Ed, Good research going on there! I think the tube will help. I went with the 1/4" shaft because of availibily of hardware in that size. I tried to find 3/8 shaft bearings to no avail but I'm sure there's some metric next size stuff. First evaluate what we have and go from there. Live and learn!

Welded-in tubing between the arms will remove the torsion bar "winding up and un-winding" . . . but you'll still have a pretty bad bending moment between the inner arm and the frame mounted bearing (as Hydraulic suggested). I'm putting my money on the brake pivot rod bending within the first three cautious and gingerly test rides.

Some easily turned aluminum pieces could be whipped up to house either larger ID ball bearings or bronze bushings to work with larger tube. I could turn some simple flanged cylindrical pieces to your specifications on my itsy-bitsy Taig lathe . . . and I have a small inventory of 6061 Aluminum round stock and some bearing bronze to work with. (Is this a sneaky way to attempt to get in on your scooter build or what? ) I have 1.75" dia aluminum (and smaller) on hand - and bronze stock to make bushings for 3/8 or 1/2" tube. (and if needed, I'd bring in some larger diameter stock . . . so I'd have some on the shelf for some as yet unidentified future project).

Wait just a second . . . I also have black delrin/acetal on hand. It might work for a semi-super light weight design where the bushing/bearing mount IS also the bushing. (Imagine your bearing assemblies out of single pieces of delrin with bores sized to the brake pivot tube.)

Food for thought.

Ed

Ed

I like delrin.

Here's a few more thoughts worth considering and discussing. When I pull a 6" aluminum front brake lever with my hand, I can stop the bike sufficiently. The rear brake lever is 5". Required braking forces on the rear are substantially less than the front due to weight transfer. The maximum force I can apply to the 5" lever is my entire weight which would be unlikely. In reality I'd probably putting hand like pressures no more than the front brake. This is not to say that my entire weight couldn't bend the shaft and should be designed for that scenario. Hmm, my entire weight could break most hand levers. All things to consider.

Some thoughts that come to mind are a stronger 1/4" shaft material to replace the soft iron. The length needed is 7". A search for a 1/4 x 7" hardened bolt has not yielded any results so far. A shorter bolt could be used by sandwiching the two bearings on the same side. A 1/4" drill bit is available which might break but not bend. All of these materials need to be welding compatible or a new mounting scheme figured out to mount the levers on the shaft. A larger shaft would certainly be better and maybe I can find bearings of the same outer size with larger inner size. Hey, just thinkin' here!

My thoughts are that it will probably work as is but as a prototype, now is the time to act if necessary.

Hey Ed! Thanks for your input and thinking outside the box, always appreciated and the same goes for the rest of the gang.

Fun stuff, engineering.

Maxie

PS---I did some somewhat crude testing with a 12" wrench and the shaft vs a standard bolt. The shaft material bent at about 15 foot pounds and the standard bolt at 25 foot pounds. I'm sure a tougher bolt would far exceed those numbers. I doubt we could generate those forces with the levers and linkage as designed now but doubting and testing are two different things.

OK, it's about an hour later and I'm still fiddling with measurements. A measurement at the front brake lever for a really hard pull is about 26 pounds but it's only about a 4" lever which means I'm only generating about 6 foot pounds into the system which gives a redundancy of 2-3X for bending the shaft at 15 foot pounds. Enough? We'll see.

After all this fun testing and engineering, our weak point (maybe) seems to be the 1/4 " shaft bending from the bearing out. I think the answer is to extend our proposed tube or sleeve over to the stop collar on the outer bearing. It could go through the inner lever or two sleeves could be pieced around it and all welded. What could go wrong I always say.

Maxie

Maxie,

Just so you'll know . . . at my end it would be pretty quick and easy to make the pieces I've suggested. As evidence of that, see the end-grain oak piece in the photo below. It is sized for 1/2 tubing - though I suspect the center-to-center distance between the mounting holes is a bit small. All that would be left is to part it off the end of the branch . . . and cut file the excess off the flange.
I recognize that you already have considerable effort invested in the 1/4" shaft design, but you haven't sold me yet that it won't bend quite easily at the bearing. The test that is needed is applying your test force to your foot brake toe pad lever arm (note the length) - which gets multiplied by the leverage ratio of the toe arm and actuation arm - and apply that "leverage increased force" to the end of 2" of cantilevered 1/4" rod. I don't think you'll like what you see . . . but the pre-Thanksgiving "honey do" list won't allow me to jury-rig up such a test. (Especially since I've already fudged production of an oak mount and writing this message into the schedule )
Ed

DOH! And here is an even simpler idea. I could turn delrin bushings which would fit into your existing bearing mounts. Press out the ball bearings, press in the bushings. Voila!

Ouch, OK Judy! I'll get back to sharpening those knives!
Ed

Max,

Comparing front brake pressure to rear brake pressure is not an apples/apples comparison. Whether front brake does 70% of the work or not, you activate the front brake with your hand, and the rear with your foot. Don't know about you, but I can play piano and guitar with my hands but not with my feet. Fine motor skills and gross motor skills, not the same thing. This is, IMHO, why rear brake parts are beefy and front levers not so much.

There are other ways to go on brakes for your ride. Convert to disc brakes with hydraulic activation. Parts are available for most dirt bikes these days, including the little guy bikes, they are cheap enough, easy to use, and adaptable from ride to ride with a little bracket making. Hydraulic discs also don't weigh all that much. Find a very used, not expensive, dirt bike with hydraulics that has been reduced to a parts bike, and swap parts. Then your rear sets will work directly on a master cylinder without redirecting thrust.

Great R&D session. One option might be to press another bearing with a larger ID into your flange mounts. A 1/4" shaft might be twisty, but 3/8" or 1/2" shaft would not be. Hit the online bearing catalog. You might find flange mounts with the same OD and bolt pattern with the larger ID and save time on the modification. Or a two-diameter shaft: 1/2" between the two levers and the righthand flange mount, and 1/4" across the bike to the small-ID lefthand flange to save weight.

Many options.

Hey Jack, Hmm, brakes are brakes on these models of Hodakas. Front and rear share the same components such was levers and brake shoes. They both do the same thing and generate the same forces with basically the same components and the same physics. Harry Taylor's famous road racer demonstrated that front brake cables activate rear brakes. The piano I played also had pedals and I didn't break them off. I'm also having trouble believing that you can bend or break 1/4" shafts with the input of a four inch lever and hand or toe pressure. Just giving you a bad time Jack.

In my build-as-you-go design it appears that it has a weak point and the question is what are its limits? We could jump on the rear lever with full weight and eventually break or bend the weakest link. My bet would be on the aluminum rear brake lever. My point is that something will break with abuse.

I think we all agree that that the soft 1/4" shaft is suspect at least for abuse but not necessarily for standard use which would include road racing. Most problems have a solution and the solution is to get the shaft up to strength to our supposed specifications. Some things we can do are obvious. A bigger shaft could add the needed strength but we are somewhat but not totally committed to my 1/4" design. After talking to an engineer friend last night, his advice was to replace the soft 1/4'' shaft with a "real steel" shaft of the same dimensions. This is the stuff used in motor shafts, drill bits and other industrial uses. He will supply the needed shaft next week.

Meanwhile I've procured the needed collars to be welded between the both the levers and stop collar. Probably overkill in my opinion but adds maximum strength with minimum weight gain. I think we'll be back in spec soon without changing horses mid-stream.

Maxie

With the welded on sleeves from the outer actuation arm all the way to the bearing . . . it just might work (assuming use of a higher grade of steel for the 1/4" rod, which you have on the way). And this all certainly fits into one of the concepts of prototyping - build it light, then go back and beef-up the items which show they need it. It might end up that the 1/4" shaft design as it has developed thru the iterations it has already had . . . may not need beefing up. Fun Stuff!

Eat till it hurts!

Ed

You could always mount a pillow block above the frame and mount a bushing there. Then get rid of the extra bearing and shaft going to the far side of the engine. And yes my terminology isn't correct but you may get the drift. Harraw for the fun, is the hodaka done. --------Clarence

Thanks Ed! Somehow I'm going to a noon Thanksgiving followed by a 7 PM thanksgiving. I'm plotting how to pace myself for maximum consumption which strangely is all part of the Thanksgiving experience. The good side is we'll see family and friends on the great American holiday with the added bonus of desert which can even carry over until breakfast. Looking forward to it even though I've been accused of being a Bah-humbug guy!

Happy Thanksgiving to all!

Max

It's not just me.

" I'm putting my money on the brake pivot rod bending within the first three cautious and gingerly test rides....Ed."

Nor am I suggesting that you stand on or jump on the brake lever with your full weight. The point is simpler than that. It has nothing to do with the size of the brake shoes or drums, or the size of the cables. It has to do with which part of your body controls input to the brakes. If you put both brake levers on the handle bars,hand levers will work fine. If you use a hand brake sized cable to activate the rear brake, that will work also. If you use your foot to activate the brake, you can't modulate input well enough to get by with light levers.

I never bent a foot pedal on a piano either, but show me a piano foot pedal that is the same size as a key on the keyboard. Even on a device invented hundreds of years before the motorcycle, someone figured out that a foot pedal has to take whatever force your foot generally provides.

Running a collar from lever to bearing will shorten the bending moment. That's true. It will also focus all bending moment on a single point rather than over the length of a rod. It will still bend. One way to find out.

The idea of mounting the rod between the levers in a pillow block will work. It will transfer all of the bend (as opposed to twist) into the frame where it belongs. Then, as long as the rod between the levers is sufficient (to handle the twist), and the pillow and brackets are sufficient, everything will work out.

All of these suggestions are based on years of fabrication, so quite aside from looking up data on the torsional resistance of whatever grade of steel you use for the pivot, experience supports conclusions as well. You are free to complete and test your system, and at this point you should do so.

taber hodaka wrote:You could always mount a pillow block above the frame and mount a bushing there. Then get rid of the extra bearing and shaft going to the far side of the engine. And yes my terminology isn't correct but you may get the drift. Harraw for the fun, is the hodaka done. --------Clarence

Hey Clarence, I didn't get to answer your Thanksgiving post as I was off to two giant meals in one day. At least they were spaced properly, noon and 7pm. I'm still full and It looks like pumpkin and apple pie for breakfast. Not all bad. The Old Man went South for the Winter and we didn't have to feed him this year.

Back to the pivot shaft. I did consider the pillow shaft on the frame but all that I could find were too tall and I hated to mount something on a tube and it also looked unacceptably clunky. The simple shaft mounted appeared to be the way to go and I think it will work fine and I'm quite happy even though Jack isn't. Hey, we're not stopping locomotives here with 5'' levers. All in fun gang!

Max

Has Winter arrived?

I suppose real engineers always have back-up plans and alternate approaches in the prototype stage. Being only an amateur engineer I'll still research an alternate solution with minimum effort. If our shaft isn't strong enough we can start globing on strengthening measures (which I've done) that probably work. The real solution (if needed) is a bigger shaft. A bit of research and I find a 12mm ID bearing that uses the same carriage and will bolt directly in with a shaft almost twice the diameter but over twice the weight. At this point we might consider a 12mm tube if available and meets strength requirements. We don't want add over 1/4 pound if not needed.

I still prefer my design as the bearings are mostly hidden and the simple shaft solves the problem of the limited space. This is how it's going to be at this point sez the head engineer. I do have a back up. Should the bigger shaft be installed it would be a good time to change the components to stainless steel for durability to the elements and improve the visuals.

Maxie

More research and this bigger shaft idea is looking promising. This is still a prototype. Bolt on 12mm ID bearings to replace the 1/4" (6mm) and 12mm stainless steel tubing with 2mm wall thickness replacing the shaft. Levers then could be re-fabricated in stainless which would really look good. The bigger diameter tubing would probably be much harder to bend than the 1/4" wimpy steel shaft. All these specs needs to be checked out of course and the modification would be relatively simple with no modifications to the frame. The assembly would look better in stainless and hopefully be somewhat bullet proof and corrosion resistant.

Still plotting,

Maxie

Max,

If your quarter inch rod does bend in use, changing to 12mm would be much better, but stainless steel has very different working characteristics than carbon steel. Generally, stainless is harder than, say, grade 2 carbon steel, but is nowhere near as strong as, say, grade 8 carbon steel, simply because stainless isn't readily susceptible to heat treatment. Stainless tubing available at the hardware store will be on the soft side. You were considering using a hardened bolt as a rod source, and that would be much better than common steel rod. But if you change to 12mm, I would stay with the hardened bolt as a source of rod. The heavier rod does not need to extend across to both bearings. Only through the first bearing. After that, you can step back down to quarter inch rod because it carries no load.

If you are really concerned about a quarter pound of brake component, change your front hub to a spindle and save five pounds. Or, consider the very slight added weight of solid shaft construction to be merely a stabilizing counterbalance to weight above the axle line. There are so many ways to reduce weight safely that a couple of ounces in brake parts shouldn't even register on the meter.

Hey Jack, thanks for the info. I need to get with my engineering friend and research stainless steel components for strength and what all those designation things mean and who can weld it. I think I'll proceed with welding the 1/4" set-up together for trials and testing measurements as it might work just fine.

As for the heavy front wheel and brake assembly, it will only be used in the road race version and engine evaluation. Realistically, no records will be broken with the wheels that are on it. Many pounds shaved and reduced frontal area will be needed. Teeny aluminum rims/spokes and weeny tires are big ticket items.The engine, frame and aerodynamic design will have to show great promise before investing in the final version. meanwhile, I'll continue the many steps needed to creep up on this theme or vision for the project. It may only end up as a fun road racer, track bike or speed trials fun, but it will be light and ready for the next step if needed. That's the theme and plan!

Max

I’m really enjoying this thread Maxie! It’s keeping me well entertained & informed! Keep up the good work! Victor

Hey thanks Victor! I too need to address that workbench. How does that happen? I really did straighten it up last week. Carry on!

Maxie

Mine is a mess from doing plumbing repair work in the garage. Everything kind of ended up on it that didn’t have another place to go. But soon! And now I’m going to have light!!! Victor

I think I can safely move past the rear brake enduro at least as far as any more frame modifications in that area. The shaft can used as is or later converted to the larger shaft stainless steel version at my leisure and the rear set shifter works well. I'm trying to get all of this mechanical stuff figured out so I can get back to working on the frame. Some of the issues are fork stops, cracks and fixing DPO sillyness which includes several bad ideas at least for my use. Strangely most of the failure points are where the DPO tried to re-enforce things and that's where they broke. I removed the back fender brace with my bare hands.

Another major project is getting the wheels acceptably polished and tires mounted. The wheels are fair but need a major polishing of the hubs and spokes hopefully without taking any wheels apart. Always time consuming but Winter is coming. I'm off to Ace Hardware to replace Dremel tool brushes from the last wheel marathon. This will keep me out of trouble for a while anyway.

More planning than action on this post but ya gotta have a plan.

The report of the day,

Maxie

Good progress on the rear binder. You've got many of the initial design questions resolved, so backburner them, let them simmer, and see how they taste in a couple of weeks.