StarDestroyer.Net BBS

I'm thinking in the future of slightly altering the rear brakes on the Russian bike. Just a little bit. [/lie]

At the moment, the rear wheel and sidecar wheel are two entirely separate brake systems.
The rear (bike) brake is a traditional drum--lever and rod operated from a foot control.
The sidecar wheel brake is a drum operated by a control cable from a parking brake lever. It is only used for parking.

This leads to neither brake being as strong as they could be, and the bike will naturally try to turn when either brake is operated.


What I'm proposing is to link these two systems together into one, so either control will operate both brakes simulataneously. See the picture:



So each brake lever is attached to a pulley. Around these pulleys runs a control cable. When either pulley is, well, pulled, it pulls the control cable, which then naturally pulls on the brakes at each end.
(You ever notice how if you say a word often enough, it starts to look weird?)

What I'm looking for here is someone to poke at this and tell me the problems. It looks good to me, but at the moment its a spherical vacuum with frictionless cows.

Details
* The force being applied to each brake SHOULD naturally be equal, translating to equal braking. If it's not equal, or it is and for some reason I need it to be not equal, I'm not sure about how to adjust individual brakes.
One idea I had was a friction clamp on the cable at that side, increasing the resistance to force, but that works both ways (resisting the brake returning), and I think the resistance would tend to alter with use. Another idea is a spring, increasing the resistance on that side--it would actually help to return the brake, and the resistance can be tuned by pre-tensioning.

* I want to be able to disconnect the sidecar and ride just the bike, and so the new brake would have to be able to deal with that. I'm thinking the control cable is actually two cables hooked together, and when unhooked the loose end is attached to a spring to simulate the missing sidecar brake.

* The control cable would be in a sheaf around the pulleys, and the whole sheaf is being pulled. I don't know if that would cause undue wear to the cable.


OK. Questions? Problems?

Liability issues means that those of us sort of qualified to respond probably shouldn't.


You have identified some of the main challenges - ensuring the connect-disconnect for the cable between the bike and sidecar is robust at impact situations is another.


Accounting for the different amounts of cable stretch due to different cable lengths between level and brake is another. This includes slack increase from cable warming up on long journey.


Accounting for the different centers of mass for a full sidecar and an empty one to avoid turning when braking is another (is turning when braking desired for some bikes?)

This system is beggin for problems, methinks.

Asymmetrical, two inputs, moving point of force application...

The pulleys are the worst thing - due to the assymetry and probably unequal resistance of the breaks due to the angles of force imparted, it is quite likely that this would result in a skid-stering setup. if you want to use this sytem with two different input levers, I would propose to run two separate lines each to each control (4 in total.)

First, this eliminates any way of force inequality due to a pulley sticking, uneven pull at the ends, the wire slacking, rubbing or getting pinched somewhere.

Second, you do not have a random wire moving somewhere inside the vehicle that could snag somewhere. You end up with 4 lines running inside of tubes that can easily laid out and stowed, and all inputs will have the same operation travel on both brakes, if done properly(and adjustable). The current setup is unable to balace break power.

Third, if one of my proposed four wires snaps, you still retain 50% operation in one input device, and 100% in the other. in this current setup, if any of the lines (input1, input2, connector) snaps, you lose all brakes, completely.

I have two trains of thought in my head. They're intriguing in that they're mutually opposed to each other, and yet they're both perfectly happy to chug along besides each other.

One is that I'm out of my depth here--I lack the knowledge necessary, it would require testing rigs, and anything I built would never be passed by an engineer anyway. Throw it in and go on with all the other things I have to do.

The other is that if I use threaded rod passing through a plate at the connection between the bike and sidecar, I could easily slip a spring on there and pre-tension it with nuts--weld some nuts on the end of the rod to attach the ends of the cables to, using eye terminals--I think pulling on the cable sheaf is a bad idea, instead have a break in the sheaf (two separate sheafs on the one cable) so the pulleys can act directly on the wire and the sheaf can be fastened down...

Yeah, those two trains should not be able to run on the same track.

Anyway, lets see here:

Liability issues - Yeah, didn't think of that. While I like to think I'm not the sort of person to throw someone else under a bus to save myself, it's probably best not putting it to the test. Anyway, someone else could read this and decide to try it who is.

Liability Disclaimer for anyone reading : I am not a trained engineer. I am not even a trained frigging mechanic. I have no qualifications whatsoever. Anyone using these ideas be aware they're coming from someone who probably knows LESS THAN YOU! If you kill yourself, don't come whinging to me.

Accounting for the different amounts of cable stretch due to different cable lengths between level and brake is another. This includes slack increase from cable warming up on long journey.

When you say "level and brake", what exactly do you mean? Otherwise, I think I would try to minimise stretch by using an unnecessarily heavy cable. I've never noticed any significant increase in cable length in cable brakes I've had, although this would be magnified by a much longer cable. Should be calcuable, though, standard expansion rate at normal temperatures; the cable can't get that hot, it's a brake cable, spends most of its life not doing anything.

Accounting for the different centers of mass for a full sidecar and an empty one to avoid turning when braking is another (is turning when braking desired for some bikes?)

Turning when braking, or accelerating for that matter, is not so much desired as just a fact of life. Under acceeration you veer left off the road, under braking you veer right into oncoming traffic. Although you can totally use it--I've already experimented with hitting the brakes going around roundabouts and letting the sidecar carry me around.
If I can put some braking on the sidecar while moving (instead of it being just the parking brake), even if not balanced, it should reduce that veering action.

This system is beggin for problems, methinks.

Probably

The pulleys are the worst thing - due to the assymetry and probably unequal resistance of the breaks due to the angles of force imparted, it is quite likely that this would result in a skid-stering setup.

As mentioned above, it already does that. I don't think it would be possible to make it worse than the starting point of an unpowered, free-running heavy mass on your side.

if you want to use this sytem with two different input levers, I would propose to run two separate lines each to each control (4 in total.)

First, this eliminates any way of force inequality due to a pulley sticking, uneven pull at the ends, the wire slacking, rubbing or getting pinched somewhere.

While I believe I can balance and adjust the forces at each end by an adjustable pre-tensioned spring, you're right that if a pulley sticks, it will throw that off.

Second, you do not have a random wire moving somewhere inside the vehicle that could snag somewhere. You end up with 4 lines running inside of tubes that can easily laid out and stowed, and all inputs will have the same operation travel on both brakes, if done properly(and adjustable). The current setup is unable to balace break power.

Although I don't see why one sheafed wire should be harder to route safely than four.

Third, if one of my proposed four wires snaps, you still retain 50% operation in one input device, and 100% in the other. in this current setup, if any of the lines (input1, input2, connector) snaps, you lose all brakes, completely.

Not quite. You've still got your front brake. Separate system.
That's not actually ignoring what you're saying about losing rear brakes, however.

Korto wrote: ↑2018-11-13 08:33am

The pulleys are the worst thing - due to the assymetry and probably unequal resistance of the breaks due to the angles of force imparted, it is quite likely that this would result in a skid-stering setup.

As mentioned above, it already does that. I don't think it would be possible to make it worse than the starting point of an unpowered, free-running heavy mass on your side.

if you want to use this sytem with two different input levers, I would propose to run two separate lines each to each control (4 in total.)

First, this eliminates any way of force inequality due to a pulley sticking, uneven pull at the ends, the wire slacking, rubbing or getting pinched somewhere.

While I believe I can balance and adjust the forces at each end by an adjustable pre-tensioned spring, you're right that if a pulley sticks, it will throw that off.

Second, you do not have a random wire moving somewhere inside the vehicle that could snag somewhere. You end up with 4 lines running inside of tubes that can easily laid out and stowed, and all inputs will have the same operation travel on both brakes, if done properly(and adjustable). The current setup is unable to balace break power.

Although I don't see why one sheafed wire should be harder to route safely than four.

1.) Right now, your setup is kind of predictable. If you use eiter of the systems, it will react the same - use the sidecar brake, it turns to, use the bike brake, it turns the other way. If you have the pulley system linking it like this, it could react in any possible way, depending on multiple factors that are random and out of control. So you never know which direction and how hard it will veer when hitting the break.

2.)We agree on that - and I know from personal experience that no amount of pre-tension (apart from completely bolting everything down to non-moving) wil prevent a pulley from sticking or throwing the cable of if the system is affected by shock, say, a pothole.

3.) Because these 4 lines will not move. They are bolted down, and on one end there is the input lever, and at the other end is the brake. If you step on the bike break pedal, it pulls the two lines to either brake taut, and the two lines of the hand brake slacken a bit. You use the hand brake, and it happens the oher way round.

For the pulley system to work, you need to have this cable that is able to move as the pulleys move. So you have one cable that is mostly unsupported at least between the between the pulleys, and will change its position inside the bike - when one pulley is pulled, it will move forward, causing the wire to follow, which changes the angle it runs between pulleys, as the both pulleys will also want to come closer to each other as the force demands... So instead of a 4 sheathed cables strapped to the frame for most of their lenght, that can be put anywhere our of sight and reach, you need a moving cable that is fed through a - to be determinded by testing and non-negotionable positioned - "cylinder" of air that needs to be free of obstruction and safe for operator and passenger to not be caught by. Then you need to have a monting for the pulleys, which also need wiggle room to move forward and back, but also have to be restrained against movement towards the other pulley on being actuated. That means a lot of jerry-rigged stuff that have to be purpose built, fitted, tested, and meddled with to fine tune, for a system that is inherently sub-optimal, instead of 4 pieces of readily available, proven to work commercial brake line. From an installation standpoint, it is inconvenient.

Considering the time needed to make all these parts & fitting them, the cost of suitable and durable pulleys, cable, fittings, etc - it most likely will turn out to be cheaper to spend a bit more on the two extra brake lines you need (since two of them are already installed)


Since engineering is the art of forseing how things can fail - what if it snaps in use?

Most likely, it will snap while breaking, right at one of the ends, at either of the brake attachments. Since it is under tension at that time, it will most likely unravel and get pulled away and out of the pulley system.
That lenght of loose wire (with one end still attached to the other brake) will end up somewhere. And since it has to be in front of the wheels in order for this system to work, it will most likely end up in the drive train, somehow, because worst case always happens. Which might result in the other end snapping as well, but only after a healthy pull on the brake it is still attached to. So you would go from brakes -snap - no brakes - one brake blocking due to line catching, followed by either a careening screeching veer to a stop if the line holds, or another occurrence of no brakes if it snaps. And maybe a stalled engine.

You could always go super modern and use an Arduino to take input from the brake levers and output through linear actuators.


You won't get even braking force through your twin pulley idea, which ever brake input you use will apply more force to it's brake, and probably activate before the slack gets fully taken up and the second comes on.

2.)We agree on that - and I know from personal experience that no amount of pre-tension (apart from completely bolting everything down to non-moving) wil prevent a pulley from sticking or throwing the cable of if the system is affected by shock, say, a pothole.

Arrrgh! A spherical cow!
I had given NO consideration to the idea of the cable being bounced out of the pulley (actually, that might not be quite true--I have a dim recollection of considering the problem some time ago, and coming up with no solution I was comfortable with at the time, so I put the problem on the back-burner in the hope I'll think of something later, and then forgot about it. Well, it's later, and I still haven't thought of anything).

I could use half-circles of pipe instead, and have the inner core of the cable running inside the pipe. This would increase friction, but since the pipe is fixed, it would at least be consistent. Or use some outer sheaf as the half circle, fixed in place on the puller.

To prevent the cable flapping around loose in the even of a snap, the cable sheaf would have to be fixed down, as is normally done with cables. I can see it in my head, but it's too late and I'm too tired to draw it now.

You won't get even braking force through your twin pulley idea, which ever brake input you use will apply more force to it's brake, and probably activate before the slack gets fully taken up and the second comes on.

I still feel that a pretensioned spring can be used to balance the force between the two sides, although it would be best to keep the cable runs as straight as possible where possible. Testing could give some interesting data, if this ever gets even that far.
In my favour is the parking brake doesn't have to act in a smooth fashion, it doesn't matter if one wheel brakes before the other, and it doesn't matter if it takes quite large movements of the lever. If I'm using it, I've already stopped.
The foot brake has to be reliable and work with only a few inches--although it can be quite heavy to use, that's fine.


This is becoming increasingly theoretical. I feel at present the issues make it impractical, although I'll still be thinking about it. Maybe when I've built our new house and I've got a workshop I can fiddle around with it. So no time soon.


Plan B is a set-up from a later model bike, where they keep the standard rod for the rear brake, and hook a cable up to the sidecar brake.
The cable's too short, as the sidecar's on the wrong side and it's a wider car, so that needs to be lengthened; and the law requires a handbrake to at least the sidecar wheel, so I'd need to also hook that on, but I don't actually need the handbrake to the rear bike wheel. It just seemed more elegant.
Quite similar to what you were suggesting, LaCroix, but with one less cable.
I'll be honest and say that if anything happening, that it would be this.

Not even vaguely familiar with what you're planning but from the perspective of someone who deals with pulleys and cables.... I agree with LaCroix.

If you want/need to use two separate input levers to control two sets of brakes... go for four linkages (or three if you only want/need one lever to control one brake). Your first diagram, looks sweet on paper but even if none of the other problems listed arise you will never get equal force on both brakes.

I don't think you will ever get balance out of a cable brake system like this, that's the whole reason why hydraulic brakes are a thing even on some peoples bicycles. A cable is too elastic and has too much friction on it's run. I doubt it will actually be dangerous, or rather not more dangerous then it probably already is, I just highly doubt it will worth enough to be worthwhile project. Maybe if your prepared to constantly tinker with the tension it would work out as weather conditions change, and the cable heats up anywhere it might run near the engine...


Cable brakes are such a pain in the ass on motor vehicles that a lot of cars actually only have the cable parking brake work on one wheel, or if it works on both wheels it common for it to get out of balance anyway over time. Depends a lot though on details, back when we had drum brakes on the rear of all vehicles it was much easier to make a good emergency brake, they'd have the mechanism operating on a smaller drum inside the hub.

Actual "Equal force", while nice, was never the requirement for success. "More equal" would have been sufficient.
But I'm dropping the idea. While it looks simple on paper, LaCroix is right that the cable will jump loose, particularly hitting a bump while releasing the brakes, and then it'll jam.
I could instead of little pulleys, have the cable outer sheaf fixed in tight curves, and the wire sliding inside to make the bends. Can't jump out then. but thick wire (to mitigate stretching and breaking) going around multiple tight curves? A lot of resistance, a lot of imbalance in force, wear and tear on the cable, etc. Other alternatives involve short lengths of cable and joining to multiple pivoting arms--which multiplies out the failure points horribly.
And all this is ignoring all the other objections.

Like I said, I'll just use the double-brake that came with the MT-11. It should fit straight over.

I never mentioned, but a fair time ago (a couple of years? Perhaps), I actually bought the parts for the mt-11 sidecar brake, and having given up on my pulley idea, I pulled them out again.

And promptly got reminded why I tried to think of something else.

The brake lever is a little bit different, but nothing that couldn't be massaged in. The real problem is the cable. This was made to have the sidecar on the right, so the car is right there next to the brake. In Australia, the car is on the left, and the most convenient way for the brake cable to get oer there is straight through the bloody wheel.
As that is likely to have technical difficulties, it would instead need to do a tight 180, followed by another tight 90 to get around to the right side. With a heavy cable. It may be possible, but I don't like it.

Got another idea.
Here's the current lever-and-rod arrangement

And a picture (It's hard to actually capture in a photo what's easily seen in person. This is the best of a few attempts)


So the problem here is trying to turn the direction of motion basically 270 egrees without losing too much force. I'm thinking if I attach a push-rod to the other side where the pull-rod goes to the brake, it can push an L shaped lever, which can then pull on a cable, running much more straight and smooth to the sidecar brake. At the brake, I'll attach the parking brake cable to the rear-brake cable, for a 2 into 1 arrangement.
Something like this, the mechanism on the left hand side. The original stuff is in black, the add-ons are in red.

As you can see, the push-rod pushes the L lever, which pulls the cable. Simple.

The pull-rods working the brake are thin, just M6 as I recall, but they're pulling. Pushing is a different matter, and I think they'll need to be much chunkier. To make a fork end to go over the existing pull-rod connection, it would need to be a total of 24mm across (the existing connection is 16mm, add in 4mm on either side), so I could just do it with some 25mm bar, and cut out the needed forks, all as one solid lump. Certainly that'll be strong enough, but it won't give me any adjustment if I find the rod is a tiny bit long or short to work properly. I prefer two halves made to slide across each other and tightened with two screws. If fine grooves can be milled into the two faces of the metal where they meet so they lock together, it should be completely solid (bottom right, a top and side view).
The L lever I think would be best cut out of one piece of solid sheet if I made it (no relying on my welding), like on the top right, but with a deep spacer welded on to give the thing more rigidity on the axle (which would probably be a bolt, screwed into a nut welded onto a base-plate the lever mechanism sits on).

Can anyone see likely problems with this?

Please don't answer if you're qualified enough that you could be liable.
And remember, I don't have any qualifications. Anyone using these ideas does so at their own risk.

I don't see any problem with that, but you might want to play with the bend lever angle... a different angle might lead to a better mechanical advantage over the various stages of travel. Same for initial and final position of the lever.

You want maximum leverage at the end of travel, when you actually press the brakes the hardest. A 90° start angle means that you have the most power in the beginning, when there is no brake contact, yet. This will lead to you having to break much harder for same effect. Just twisting the starting point by 45° might make your brake feel much softer in the hand, while optimizing brake effeciveness.

I suspect it works in plan, but once implemented with small angles and the torques created by shear between different vertical layers...

Perhaps a test bed.

LaCroix wrote: ↑2018-11-28 05:25am I don't see any problem with that, but you might want to play with the bend lever angle... a different angle might lead to a better mechanical advantage over the various stages of travel. Same for initial and final position of the lever.

You want maximum leverage at the end of travel, when you actually press the brakes the hardest. A 90° start angle means that you have the most power in the beginning, when there is no brake contact, yet. This will lead to you having to break much harder for same effect. Just twisting the starting point by 45° might make your brake feel much softer in the hand, while optimizing brake effeciveness.

I could make the bend lever so the angle between the two arms is adjustable, although I'm not sure any advantage would be worth the extra complexity.

Good thought about the start and end point for the lever. I was thinking before I would start it a little before perpendicular, and it would end a little after, to try to minimise the side movement, but you're right, the most force is at the perpendicular and that's where it'll be best to have the end point so I can put the most pressure on the brake. So instead I should look first at having it start enough before perpendicular so it'll finish on the perpendicular, and play around from there.

I'll definetly go for the adjustable-length push-rod. It'll make adjusting the lever start position easy.

I suspect it works in plan, but once implemented with small angles and the torques created by shear between different vertical layers...

Well, all I can do is try to minimise the angles and shear as much as I can. I fear it may end up that the best test-bed will be the bike itself.
We definetly need a resigned shrug emoji.

For how much trouble all of this is, why not just look into converting the vehicle to use hydraulic breaks on all three wheels? Is that actually going to be harder?

In good part because I have no real idea how to go about it, while I feel I have a fairly good grasp of this mechanical setup.

I feel it would involve replacing a lot of parts (I could be wrong here, see point 1), while this just requires a push-rod and lever, hooking up to a cable--just adding on to what's already there, not removing anything, and I could easily remove the added bits and put things back to original.

I also feel it would be significantly more expensive.

I also want to be able to easily separate the sidecar. With the cable, I can just disconnect it at the lever. I don't see how to do that with a hydraulic pipe.

I have none-the-less tried googling hydraulic conversions. I so far haven't felt illuminated.