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Foot Cramps

24 posts in this topic

Posted

Hi Everyone.  Lets discuss brakes.  I have the latest matco brake cylinders installed with double puck brakes.  Why do I need to practically stand on the brakes to get a solid stop and in the process cramping up my foot every time.  I have the cylinders very close to the pedal at top connection.  The brakes just don't seem to be performing like they could.  Am I missing something other than stronger feet?  What can I expect from double puck brakes since I have not other plane with same setup to compare to.

Thanks

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Posted

Your pedal geometry is probably wrong.  If the cylinder attaches to the top of the pedal, you actually lose mechanical advantage as you apply the brakes.  You start out with about a 1 to 1 mechanical, and it drops to .7 to 1 as you push on them.  Matco recommends a 2.5 to 1 mechanical advantage.  I redesigned my pedals to get this, and I went from not being able to hold the plane at 3000rpm (a little tough to do a runup), to no problems at 5500rpm.  Attached is a picture of what they look like after redesign.  I had to switch from the Matco cylinders with the internal reservoirs (5C?) to the shortest ones they make (4G or 4H) with an external reservoir to make them work.

brakepedals_small.jpg

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Posted

I'd agree that it is probably geometry. I've seen this so many times with experimentals, especially with Matco brakes for some reason (likely because they are cheaper and more builders use them). 

Do you have a picture or two you can put up so we can see what's going on? Never know, it might help! 

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Posted

I can post a picture tomorrow.  Thanks

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Posted

I can post a picture tomorrow.  Thanks

Photos always help solve problems.  One other thing is that the Matco MCs went from 1/2" bore to 5/8" bore - they make a sleeve for the MC-4 to make it 1/2" bore like the early ones.  I am not sure that this is part of your problem, but it has helped others.  The other thing is the geometry and getting that 2.5:1 ratio, and also the "give" to the open top of the pedals as originally designed.  C5Engineer has posted pictures of the mods to the pedals.   EDMO

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Posted

I tried the 'intensifier kit' you are talking about Ed.  It probably made some difference, but it wasn't significant.  Not worth the time or $$.  Fix the pedals so the geometry is right, or at least close.

Mark

 

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Posted

Pedal geometry is hugely important.  I too have dual calipers per wheel, but went through 3 pedals before i got it right.  First I didnt have enough brake, then I went to the other extreme and was able to lock them up while landing only using my mind.  the third iteration was around 2.8 to 1 and is perfect.

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Posted

There are 3 brake pedal threads going on right now all discussing the same thing. I posted pics of both my modified set ups in the general area.

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Posted

Pedal geometry is hugely important.  I too have dual calipers per wheel, but went through 3 pedals before i got it right.  First I didnt have enough brake, then I went to the other extreme and was able to lock them up while landing only using my mind.  the third iteration was around 2.8 to 1 and is perfect.

how did you get them to the point you could lock them up.

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Posted

4:1 mech advantage on the pedals and 2 calipers on each wheel

 

 

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Posted

4:1 mech advantage on the pedals and 2 calipers on each wheel

 

 

:o

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Posted (edited)

How did you get 4:1. I don't understand the mechanics of that and what it looks like.  I already have double pucks and remote resivour. 

Edited by lv2plyguitar

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Posted

Here is the before and after pictures of my pedals with some crudely drawn notes, it might make it more clear.

 

brakes_original_with_notes.jpg

brakepedals_small_with_ratio.jpg

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Posted

Okay I see my issue now.  My brake pedal is identical to first picture.  Now I just need to find new pedals.  I don't have a welder.

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Posted

I have a welder, but I didn't trust my weak welding skills for anything very stressed.  I designed the new pedals so all the force not directed through any welds.  The left pedal is more dependent on the welds, since I had to put the attach point in the middle of the pedal, the weld has to keep that attach point from folding over.

I cut them out of flat 4130 plate, then bent them into shape and welded the two straps at the front so my foot didn't get stuck.  It took me three designs before I had one that was simple, light, and not dependent on a weld carrying the load in tension.

Mark

 

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Posted

I can already tell my cylinders are to long.  Will need to spend another 250 on shorter cylinders.

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Posted (edited)

Before you spend $$$ on cylinders, check with Mikesk, who I think now is "Saskavid" or Joey "C5Engineer" about the new pedals that Mike makes and they might work with the longer cylinders.  They say they work good.  

Mark,  I like your setup too - Looks good.   I am planning on using Cessna 150 pedals when I can get that far.  EDMO

Edited by EDMO

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Posted

I can already tell my cylinders are to long.  Will need to spend another 250 on shorter cylinders.

If I trusted my welding skills, I could have made a linkage to attached to the existing MC5 cylinders.  I think the pedals Ed mentioned have a linkage that does just that, so I'd probably spend the money on the pedals rather than on new cylinders (and have to bleed those blankety blankety blankety things again!)

Mark

 

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Posted

How do I contact Joey.  Tried to click on his name but only get an error.  Can you direct him to this discussion?

Thanks

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Posted

I'll shoot him a text. If he's available and not flying he should post up again shortly. My guess is that he's on a trip right now though. 

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Posted

Someone else told me the same thing recently I'll look into it. What's up? Did you find the other 2 brake threads that are near the top of the general area? Title is Modified Brake pedal pics.

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Posted

Joey - FYI... heres the error when clicking your name. Some, but not all, clicked names give the same error.

Fatal error: Undefined constant 'IPS\MONTH_DAY_FORMAT' in /home/content/41/11975741/html/system/DateTime/DateTime.php on line 175

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Posted

I don't clik on C5Engineer name on his post - just put pointer on his handle and the message board comes up.  EDMO

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Posted

Joey - FYI... heres the error when clicking your name. Some, but not all, clicked names give the same error.

Fatal error: Undefined constant 'IPS\MONTH_DAY_FORMAT' in /home/content/41/11975741/html/system/DateTime/DateTime.php on line 175

Doug, I get the same error clicking on your name as well. Ed's works for some reason though.

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