Mechanical disc brakes

#1
I've been studying brake calipers, and have come to the conclusion that there is a lot of friction lost between the actuation and the real friction it take to stop. A percentage mechanical advantage (leverage) is lost by the friction of all of the resistance in the cams and the levers binding. One thing I noticed is that on a floating caliper, once the lever is pulled, the whole caliper wants to shift slightly askew. This can be attributed to the anchor point of the cable is typically on the frame and not part of the caliper. Another point of binding and friction is the plungers are cylindrical with a domed head and with some wear in the caliper body it causes them to twist and lean when the rotary cam engages, putting things into a bind before linear motion starts. This is only compounded by the fact that the actuator arm is pulling from one side, making the pressure point off center.

One of the set ups that I haven't studied yet, is the POSI-STOP brake. Has any of you guys had one apart, and how does it work?

Anyway, I've come up with a few ideas to reduce friction involving ball bearings, and I think I will pursue this, just looking for some more input.
 
#2
I was curious about those too. I am going to try hydraulic brakes on my trike. I bought some used ones off a POLARIS 500 on Ebay and they have a bracket that can be flipped from the bottom to the top for easier mounting in my application.
 
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#3
I have never gotten a mechanicle disk to work good, maybe for kids its fine but adults they dont work with the acception of the mechanicle disk on my rupp c500 with pedal activated disk, although it works good pad life sucks and the rotor gets chewed up quick. Doodlebug brakes work good but the calipers crack. Upgrading to hydrolic pitbike brakes has worked for me.
 
#4
I have used Avid Mountain Bike Disc brake calipers with good success. Mechanical and hydraulic. They both lockup with plenty of stopping power. I used a mechanical caliper on my Gilson build. The below is a DoodleBug disc and wheel.


 
#5
Interesting set up, although from the pics I can't really see exactly how it works.
I've been giving this a lot of thought, and one of the ideas I want to try is mounting the caliper on a bracket that is centered on the axle with one anti-rotational anchor, much like an Azusa drum brake. I would also use the bracket for the cable anchor so whole assembly floats together.
This would keep the caliper from being distorted under pressure.
 
#6
Sorry for no explanation. Below is a picture of how it works, its mechanical so a cable is required. Pull the brake lever on the handle bars, thus pulling the cable, and compressing the disc pads. I didn't have my cable hooked up in the above picture.
 
#7
Ahh, I see. Those vertical bolts that mount the caliper to the bracket......are those some kind of cushions on both sides?
 
#8
Ahh, I see. Those vertical bolts that mount the caliper to the bracket......are those some kind of cushions on both sides?
No they are not cushions, they are metal washers, however they allow you to adjust the caliper left/right as they are cupped, helping with minor misalignments. This setup works great on my most recent build. My disc brake is a doodlebug disc, and the caliper grabs and will lock the wheel up anytime you need it to. There are many brands of hydraulic mountain bike brake levers/calipers. I would say they work better being hydraulic, but by better I mean, they grab quicker versus the cable.
 
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#9
Interesting to hear this. I've got an Avid BB7-SL Road caliper with a 140mm disc for my next bike. Very nice setup. Gonna be using a Tektro brake lever. I'm using UMI polished aluminum billet Goped wheels. Had to use Skopod adapters to get the brake disc and sprocket attached. Also had to have a little machining done on the Skopods for proper spacing, but it looks like it's going to work nicely. BTW, one thing about the Tektro levers is they provide for two cable attachment positions. I guess it's to be able to select travel and/or pressure as necessary. We'll see. I suppose you could say this bike is going to be some kind of hybrid; a mini bike with a little bicycle and Goped blood mixed-in. (ha) I've got to believe one thing........if this brake will stop a full sized bicycle screaming down a mountain road, it should have no problem bringing this little mini to a halt. Here' hoping.
 
#10
Interesting to hear this. I've got an Avid BB7-SL Road caliper with a 140mm disc for my next bike. Very nice setup. Gonna be using a Tektro brake lever. I'm using UMI polished aluminum billet Goped wheels. Had to use Skopod adapters to get the brake disc and sprocket attached. Also had to have a little machining done on the Skopods for proper spacing, but it looks like it's going to work nicely. BTW, one thing about the Tektro levers is they provide for two cable attachment positions. I guess it's to be able to select travel and/or pressure as necessary. We'll see. I suppose you could say this bike is going to be some kind of hybrid; a mini bike with a little bicycle and Goped blood mixed-in. (ha) I've got to believe one thing........if this brake will stop a full sized bicycle screaming down a mountain road, it should have no problem bringing this little mini to a halt. Here' hoping.
Sounds like a good setup. The Avid calipers, as long as there is some disc to grab onto then they will get you slowed down. Mine locks up anytime I ask it to. I know as long as you have yours setup correctly you will be happy with it. Agreed on the mountain bike, hauling down hill and it stops them, so we are asking less of them you would think by stopping a mini bike. Post up some pics of your setup when you can.
 
#11
From what I can tell by looking at pictures on the web the typical foot brake lever used on small hydraulic brakes has a mechanical leverage of about 4.5 to 1. I wonder if anyone here can add to this.
 
#12
That sounds about right considering the length of the foot lever. A lot of riders complain that rear drum brakes aren't all that good, operated with a hand lever, but when you operated them via a foot lever the leverage increases and they work lots better.
 
#13
I tried finding info on the MCP disc brake caliper like I have on my oval kart, but couldn't find anything as far as the ideal ratio. I would say your setup is going to work very well, once you get your foot lever at the exact angle you want it.
 
#14
Thanks for your thoughts, guys. I am going to bend some 3/16x3/4" flat stock into a pedal and have decided to install the foot pegs first in order to be sure the angles are as good as I can get them.
 
#15
You might want to go a little heavier than 3/16", because of the twisting factor. Once you have that kinda leverage, it's easy to bend the lever just by foot pressure. Most trail bikes and motorcycles have a forged brake lever just for the stiffness.
 
#16
You might want to go a little heavier than 3/16", because of the twisting factor. Once you have that kinda leverage, it's easy to bend the lever just by foot pressure. Most trail bikes and motorcycles have a forged brake lever just for the stiffness.
Thanks Pap, now that you mention it, that seems it could be a problem. I'm going to re-think this.
 
#18
I'm going to try some 3/4" x 3/4" square tubing for mine. It should be quite stiff for the weight.
Having re-thought this, I have decided to use 1/2" square steel bar for the brake pedal arm. I just found out that I will need more heat then a little propane torch puts out in order to bend the bar. I'll bet your 3/4" sq. tubing will work well.

I've also gone for 1/2" dia. rod for the brake actuator shaft instead of the overkill of 5/8" dia.
 
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