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GTaholic
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Discussion Starter · #1 ·
I sat home and looked at various V brake configs and made my own in Solidworks and did some FEM with 500N force (double than normal) and ended up with a 32 gr arm (22 gr in carbon fiber) and I will fiddle with good tension springs and so on.

I will make some sets if there´s a interest, they will be in 6061-T651 aluminum and later in carbon fiber if I can make good looking examples.

Creative critics are always welcome.

http://forums.mtbr.com/attachment.php?attachmentid=255979&stc=1&d=1177587968
 

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Go faster!
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Interesting. How are you going to build it? CNC?
The fixing hole looks to fragile, too much at the edge. Are you planing in using just a bolt to fix the arms?
 

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GTaholic
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Discussion Starter · #3 ·
Hi, that´s a pic on only the brake arm, bushing is drawn and will be glued in and is from JM3 bronze.

But that´s my second attempt 32 gr is not bad when it will hold up more than 500N of force at the wire stop hole.
 

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Go faster!
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Mattias_Hellöre said:
Hi, that´s a pic on only the brake arm, bushing is drawn and will be glued in and is from JM3 bronze.

But that´s my second attempt 32 gr is not bad when it will hold up more than 500N of force at the wire stop hole.
Yep looks very simple and light. 500N is alot of force!
If you know how to use all that technology build us some light and strong brakes.
 

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SUBLIM8er
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2,203 Posts
I love it.:thumbsup: You have cheered up an otherwise crappy day for me. The design reminds me of Marinovative kinda. I hope you will make them a reality and make lots of money....someone other then Sergio should. Will the pivot have bearings or pivot on brass cylinders? If it's a bearingless design PLEASE include some kind of seal. I hate tearing down my Mrazeks to repack due to the lack of a seal on the pivots. Anyway, nice artwork.
 

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the catalan connection
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can I play ?

:rolleyes:

well, just a suggestion,
do you think it would hold as well?
 

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GTaholic
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Discussion Starter · #7 ·
Axis II: Some weather sealing is necessary but it must be lightweight and easy to make.
Maybe a small o-ring between the spring and pivot bolt, but it can make some drag, it´s a give and take situation.
Bearings is not interested because of weight, a 9.5mm bronze tube is lighter and stiffer.

What&son, that´s a good design, but a bit timeconsuming for me to machine in a manual 3 axis mill, I will keep it simple and cool for a while :)

Sergio_pt: 500 N is a lot of force but I have no exact force so I think it´s a rough estimate but..

I will order a 3 axis manual mill and 2 axis manual lathe in some weeks and make something creative and it will be these brakes and then a long testing period to see if they works as they should.
 

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i don't give a shift
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863 Posts
Mattias, I gave you some input on WW. For the fun of it, I sketched up some brakes. I had made some different ones way back in 91, when Shimano was still flooding the market with cantilevers. My old set is retired and boxed up as I'm moving abroad in a few months. If I'd ever make a set again, it'd look something like the design below. This was just a quick sketch that would still need some refinement. Sorry for the image quality - no fancy CAD installed on my home PC. This was done in eMachineShop.

Font Number Symbol Graphics
 

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GTaholic
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Discussion Starter · #14 ·
collideus: that was you? I can´t remember which username is which in different forums.

These brake arms looks good!, there´s a need to simulate in FEM and see where the weak spots are, I have access to a CNC 3 axis mill, various lathes but I always wanted to buy something own and in this case manual mill and lathe so I can start in small scale and at my free time in evenings so the arms have to be simple, unfornutately less eyepleasing but no heavier.

Ceramic bearings are a good idea but it requires some special ordering = $$$$
Better in a bronze bushings in tolerance like +- 0.1 so it can fit most brake posts.

I will start in a simple form but light in the spirit of WW.
 

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SUBLIM8er
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Ceramic bearings are a good idea but it requires some special ordering = $$$$
Better in a bronze bushings in tolerance like +- 0.1 so it can fit most brake posts.

I will start in a simple form but light in the spirit of WW.[/QUOTE]

Be carefull with the selection of the size of the brass bushing- too much slop in the pivot and you get horrible brake squeel, too tight and the brake arm won't fit on the canti boss. My front Mrazek has a tad too much slop and I get some terrible brake noise unless I do some fancy pad adjusting. Just a word of caution.
 

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GTaholic
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Discussion Starter · #16 ·
Axis II: there is a tough question about tolerances for brake bosses because every manufacturer have their own tolerances, I will make something that´s precise enough and will hold a smear of grease inside the bearings.

I can´t bear sloppy brakes so I will take the extra time to make it snug as possible, other consumers will take care of this, high precision product with a sloppy fit in bearings is not a good selling point.

It´s rarely I see tolerances bigger than +-0.1-0.2 in most products I did programs to the most CNC machines in my former job.

As you know, a one product cannot fit all possible brake bosses without wide tolerances, something to think about.
 

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Please post the FEA results. I'm a little skeptical as my gut feeling would be that those arms would fatigue and crack with cyclic loading.

(Solidworks/ProE/Ansys user here)
 

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Cool project. Since you asked for criticism, I will try to help.

I was in engineering school when the Marinovative brakes arrived. I could not afford them, so I looked at the simple aluminum arms and thought that I could easily make something similar from extruded aluminum channel. But, when I analyzed the weight of all the hardware, I found that the arms were only a small part of the problem.

Even if the arms are as light as possible, you could still end up with a mediocre weight if you're not careful with design. For example, some lightweight arms require long brake shoe studs with thick washers. The manufacturers always leave these parts out when they advertise weights.

Here are some ideas for lighter noodle replacement:
http://www.fairwheelbikes.com/forum/viewtopic.php?t=49

The Mrazek no-noodle design requires longer brake cable housing, but of course they ignore that in the advertised weight calculations.

So, if you really want to reduce weight, please look at the mass of the complete, working brake system. Light arms will sell more brakes, but may not reduce the weight of the bike.

Some other design considerations:
Tire clearance
Many people today are running 2.2-2.4in tires, so your brake should have clearance for those huge tires plus some mud.

Pivot bearings-
Bronze bushings can be soldered or epoxied directly to your aluminum arms for a light, neat solution. But when the bushings wear out, your brakes will be garbage. Maybe that is OK, maybe not.
Plastic bushings are cheap, easily-replaced, and they are available impregnated with lubricant. A tube with flange would work well, as the flange could be placed between the brake arm and frame:
http://www.pobcoplastics.com/pg_50.htm
They would wear faster than bronze bush or roller bearing, but anyone could replace them in 5 minutes.

Springs-
I like the ti spoke linear spring idea many have used. It is simple, light, and easy to service. If you shape the spoke to wrap around the boss and/or frame, you may eliminate the mounting block normally placed between the arm and frame. It will be difficult to center the brakes, but WW may not mind.
 

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FYI,

I checked your force assumptions and they look OK. According to this study:
http://www.lni.wa.gov/Safety/Research/files/hand_force.pdf

The average man can grip with 106 pounds force = 471N. Linear pull brake levers have about a 1:1 cable pull vs. lever travel ratio. So, your 500N number looks like a good starting point.

If you are worried that someone will use your brakes with cantilever or road bike levers, then you need to double force due to 2:1 ratio. So, now you must consider 1000N

Mountain bikers may have stronger hands than average American worker, so you may also want to consider that.

Large companies must consider all of these factors and design a brake that will not be damaged when a big guy tries to panic stop. Their V-brake arms are likely designed to withstand 1000N-2000N force without damage. Now, you see why Avid and Shimano brakes are so heavy!
 

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i don't give a shift
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Second iteration. Since I made it in eMachineShop I should submit it for quotation just for the fun of it. This design would use internal springs, adjustable in both levers. A pressed-in brass sleeve acts as the bushing riding on a SS (or Ti) sleeve with a tolerance in the h6 range. Canti bosses themselves are just too imprecise to be used as the lever's pivot axle. The whole bushing/spring design comes from the levers I made. It's tried and tested and has worked for 10 years without requiring any service other than a bit of grease once in a while. Well, it's been a fun little exercise, these brakes will probably never be made.

Tool
 
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