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E: Engine Speet Brake installation query


Marcus Bowden

Well Known and Active Website User
VOC Member
Marcus asked Erik:
I would very much like some more of your knowledge on the modified Speet brake you have set up on your Comet after Vincent tried them and commented that they were better than his twin cable set up, but I like the thought of using the balance beam increasing the mechanical advantage and getting rid of those adjusters on the brake plate as it makes wheel removal much longer and a pain in the ass to readjust again .
 
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Gary Gittleson

Well Known and Active Website User
VOC Member
I have Speet brakes on my Rapide and don't have that much of a problem removing the wheel. I don't disconnect the cables.
On the other hand, I have a friend who wanted to use the balance beam for aesthetic reasons. He made his own levers for the brakes to make that possible. It took some trials and errors before he was happy with the leverage. That part is tricky. I'll try to get some pictures and post them. He has made some extra levers, thinking someone else might want a set. I'll talk to him about that too and let you know. I plan to take a ride on his bike and if I like them, I might put them on mine as well.
 

davidd

Well Known and Active Website User
VOC Member
I don't think anyone has ever figured out the mechanical advantage of the Vincent front brake. I have never seen it published in MPH and when I asked here I received no replies, just speculation. I suspect the speculation is correct, but the problem you run into is that it is difficult to mix and match because the formulae are not obvious. Thus, it is difficult to calculate the results beforehand.

I would suggest sticking with either system, but not interchanging parts unless you are willing to put the time into the experiment. If there is a mechanical advantage with the balance beam it is at the expense of losing lever travel. This may be fine, but it could also require a lot of fabrication (as Gary mentions) and trial and error. Also, if the brake shoes are stock it is likely that they are too flimsy to take advantage of any additional mechanical advantage.

You can use the balance beam as the adjusters if you make the beam stationary and run a cable to each end. Mike Hawthorne did this with his Flash racer.
2017 04.JPG

David
 

Marcus Bowden

Well Known and Active Website User
VOC Member
Look forward to seeing the photos and dimensions of the linkages would be handy too.
Thank you for putting this thread into an appropriate slot
Bananaman.
 
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vibrac

Well Known and Active Website User
VOC Member
I have never been convinced of the efficacy of the beam to increase pull. I believe Scott who were the only other advocates of the idea dropped it as well. The equilising of pull ( which is necessary) can be done at the lever this is how we did it on the Girdralic racer. looking at the Brampton bike we may have to leave it as standard for the moment

1567700285578.png
 

Gary Gittleson

Well Known and Active Website User
VOC Member
Well, here's my take.

Imagine that instead of a brake at the end of each cable, we have a spring with say 40 lbs/inch Hooke's constant. In that case, if we pull one cable (without the balance beam) 1/4", we experience a 10 lb force. If we use a Vincent Speet setup and pull both brakes together the same 1/4", we will have two springs applying 10 lbs resistance each for a total of 20 lbs.

It's easy to see that the balance beam will halve that force. The 1/4" movement at the "primary" end of the balance beam will be split in two, pulling that spring 1/8" and the other the same 1/8" via the 1/8" movement of the beam, thus causing a 5 lb resistance at each spring for a total of 10 lbs. So to get the same 20 lbs, we will have to move the cable 1/2".

That's a 2:1 mechanical advantage. But the levers of the actual Speet brakes were designed so as to apply proper braking with reasonable handle movement in a 1:1 setup. Using the balance beam with no other modifications would have us pulling the handle back to the bar before we have full braking. So one has to figure out how to hook up cables from the balance beam to the Speet brakes, which in standard form require a near-horizontal cable approach and to reduce the mechanical advantage. I just spoke to my friend (Tom Newman) and he reminded me that there's an article of his work on a fairly recent MPH. I'm going to try to find the issue. There's more to be said about this. I'm either going to get him signed up on the forum or act as liaison. More info to come.

Gary
 

Gary Gittleson

Well Known and Active Website User
VOC Member
That's the "other" VOC site. I still don't understand why there are two sites. I have asked. You first have to log into the other site and then go to the link posted here. The link shows somewhat blurry photos from the MPH article Tom Newman posted. I haven't had time yet to find the issue but it was sometime in the last six months or so.
Gary
 

bmetcalf

Well Known and Active Website User
VOC Member
I couldn't find it on the Forum Resources, Maybe Graham can post it.

The VOC website has a lot of info and on-line renewal that club members should make available to themselves.
 

davidd

Well Known and Active Website User
VOC Member
Gary,

Your figures seem incorrect to me, but I fully admit that I have had trouble with this approach before. If I summarize what I believe the argument has been it is that the twin cables split the force generated at the hand lever. Thus, 10 lbs. at the lever turns into 5 lbs. (per cable) at the end of each brake arm. The Vincent balance beam is different: 10 lbs. of force on the hand lever yields 10 lbs. of force on the inner cable (on the primary side) and 10 lbs. of force on the primary side of the balance beam from the sheath or outer cover. That force is in turn pulling up 10 lbs. on the timing side of the balance beam (and the attached brake arm), meaning the the 10 lbs. of pull is generating a total of 20 lbs. of pull at end of both brake arms...double the pull of the twin cable system (ignoring for the moment the different distances travelled.)

To simplify even further, I think the argument has been that the Vincent system has no stationary brake anchors where the hand lever force is lost to the frame. The Vincent has a moving brake anchor (the brake anchor is the primary side of the balance beam), that utilizes the force lost with the frame brake anchor by transferring it to the timing side brake arm. The balance beam acts as a moving brake anchor transferring the force lost by the frame brake anchors to the timing side brake arm.

I have not seen any simple explanation of the physics of the differences of these two systems and why they yield such different results. It is most likely my lack of schooling in this area, but I would be interested in know how the physics work.

I don't know in which MPH Tom's article appears, but I remember reading it. I posted the Higgins articles here.

David
 

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Nigel Spaxman

Well Known and Active Website User
VOC Member
You won't get extra braking force from the balance beam. Any lever type device if it increases force will loose movement in the exact proportion. Going back decades in MPH there are lots of people arguing that this device somehow magically increases the force on the brake shoes, it doesn't.

If for example the tension in the single brake cable caused by squeezing the lever with a force of 100 lbs and movement in the cable of 1/2" Then you will have 100 lbs of force on each end of the balance beam. If you pretend there is no stretch in the brake cables and all the flex is in the brake then you will have 1/4" of movement of each brake lever and 100 lbs force on both levers.

If you have twin cables you will end up with only 50lbs tension in each cable but you will have the full 1/2" of movement at both brake levers. (this is how the Speet system works) With the extra movement of the cables you can use much longer levers on the brake cams, twice as long in theory, maybe a bit more really. With twin cables and half as much force on each cable there must be less stretch. The stretch does seem like the waste in the system.

If you want to retain the balance beam as John McDougal did with his Speet brakes, then you will need levers on the brakes about half as long as the ones that come with the Speet brakes (they are made for twin cable that move twice as much) John modified his Speet brakes in that way.

I have the Speet brakes with the twin cable set up. With this set up you have to make sure that both cables have even tension in them when the brakes are applied. The balance beam does that automatically. You can fine tune the brakes a bit. When I first used these brakes I had levers with 1 1/8 distance between the pivot and the cable. That made the lever to hard, so I welded up the lever and reduced the distance to about .800" which works really well. The proper distance, between pivot and cable that the Speet and Vincent brakes are designed for is .875". By shortening this a bit I gained a bit of leverage. If you keep your brakes well adjusted you can set them up for a bit more leverage, and have better brakes.
 

Gary Gittleson

Well Known and Active Website User
VOC Member
Sorry, but I must disagree with some of this. When 10 lbs are applied to the primary side, that force will move two things at once, the brake cam lever on that side and the balance beam in the opposite direction which in turn applies a force to the other brake, thus distributing the 10 lbs into two halves. The brake cam lever will never see all of the 10 lbs. They are halved because the balance beam has its pivot in the center. Had it been off-centered, the splitting would have been proportional to the ratio between the lengths of the two sections, right and left.

Another way to look at is to imagine fastening a clamp to the cable on the primary side just below the balance beam and trying to squeeze the clamp and balance beam together. That's what the setup is really doing. That pulling together is obviously dividing the force evenly between the cable below and the beam above.

Still another way to think of it is this. Imagine two springs attached parallel to each other to a fixed object and a bar joining their other ends. Suppose we pull on the bar in the center with 10 lbs of force. Will each spring see 10 lbs? Whatever force they experience, they will apply in return. If so, wouldn't their forces add together and pull back with 20 lbs? If we can do that, we are well on our way to building a perpetual motion machine. If we pull with 10 but feel 20 then we are pulling with 20 so should feel 40..... It's obvious that the two springs will work together and return the same 10 lbs of pull: opposite and equal. Therefore, each spring will see and oppose 5 lbs assuming they are of the same strength.

In any case an important point is that if we are to use the balance beam to actuate brakes designed for direct pulls, we will introduce a doubling of the handlebar lever movement the system was designed for. That's why Nigel had to modify the lever. The standard lever has less leverage than what the Speet brake requires because in the standard setup, there's a mechanical advantage provided by the balance beam. And that's why if we use the balance beam with the Speet brakes, we need to shorten the levers at the brakes to reduce the leverage there to compensate for the extra leverage provided by the beam.

Another way to automatically evenly distribute the force is to use a whiffletree or whippletree https://en.wikipedia.org/wiki/Whippletree_(mechanism). I think I've seen such a setup on a bike somewhere, as well as disparaging comments regarding them. I don't remember where I saw that. Any thoughts about that?

Gary
 

Nigel Spaxman

Well Known and Active Website User
VOC Member
Gary, the first part is wrong. When you apply the brake there will be tension in the cable 10 lbs if you have very weak hands. That tension pulls up on the left hand brake lever, but it can only do that by pulling down on the balance beam (which then pulls up equally on the other side). If the force in the cable is 10 lbs at the handle bar then the force is going to be 10 lbs on both cables. You are not building a perpetual motion machine because the travel is halved.

The reason I had to modify my lever is instead of using the original type that has the 7/8 pivot distance. That is the type the Speet brakes are designed to use as well. I used a Dourhety lever because I like those. They have the 1 1/8 pivot distance.
 

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