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View Full Version : Cam Rotation: Over/under rotated



mudpig
02-28-2011, 12:18 PM
My question to all of you is this: What difference on speed, accuracy, draw lenght, draw weight, let-off, etc. does either over or under rotation of the cams make?....AND....how do you correct cam rotation? Cam sync is not an issue. The cams are timed equally in this senario.

Spiker
02-28-2011, 12:40 PM
Twist the cables/untwist the string will advance the cams.
Untwist the cables/twist the string will under-rotate the cams.
(think I got the advance/under-rotate right)

bfisher
02-28-2011, 03:42 PM
Twist the cables/untwist the string will advance the cams.
Untwist the cables/twist the string will under-rotate the cams.
(think I got the advance/under-rotate right)

I don''t know if I get it right or not either. I understand the terms over or under rotate better.

mudpig, there's a good sticky thread on AT about optimizing the rotation of Cat cams for better performance. This could be used for almost any dual or binary cam system.

I'm not sure about it myself. Essentially over rotating a cam will be increasing the draw length. It gives more speed, more letoff, and usually a harsher draw. This done by twisting up the cables and/or untwisting the string.

The opposite is true for under rotating the cams. It's explained better on AT.

copterdoc
03-01-2011, 05:30 AM
I think "over-rotated" and "under-rotated", are examples of horrible usage of the English language!

They don't mean anything, because they mean opposite things to different people. And they use too many letters (and words) to say what needs to be said.

When you draw a bow, you start at brace, and go to full draw. If you shorten the string, and/or lengthen the cables, you move the cams closer to their "full draw" position.

You advance them.

If you lengthen the string and/or shorten the cables, you back the cams up, away from their full draw position.

You retard them.

It's just like setting the ignition timing with an old distributer ignition system in a car. Same terminology, same results.

Advancing the cams, reduces draw weight and draw length.

Retarding the cams, increases the draw weight and draw length.

Always, every time, every bow, every cam system.

Spiker
03-01-2011, 06:15 AM
I only use them terms because the word 'retarded' gets banned. :confused:

scepterman30x
03-01-2011, 06:15 AM
I think "over-rotated" and "under-rotated", are examples of horrible usage of the English language!

They don't mean anything, because they mean opposite things to different people. And they use too many letters (and words) to say what needs to be said.

When you draw a bow, you start at brace, and go to full draw. If you shorten the string, and/or lengthen the cables, you move the cams closer to their "full draw" position.

You advance them.

If you lengthen the string and/or shorten the cables, you back the cams up, away from their full draw position.

You retard them.

It's just like setting the ignition timing with an old distributer ignition system in a car. Same terminology, same results.

Advancing the cams, reduces draw weight and draw length.

Retarding the cams, increases the draw weight and draw length.

Always, every time, every bow, every cam system.

I cannot disagree Copperdoc, however most people don't understand mechanical terms when it comes to advancing and retarding of ignition timing and such but when you rotate something it is easier for the masses to understand...proper english aside.

mudpig
03-01-2011, 06:16 AM
First: Thank you for all the answers. They help this newb understand things a little better.

Second: With this new info.... is it advantagious (for maximized performance) to retard the cam timing, or is it best to be at TDC 0 Degrees??

Third: Are there any downsides to retarding/advancing the cam timing??

and...I think that I've found that Sticky at AT, so thanks for that. Haven't had a chance to read and reread it yet to full understanding.

scepterman30x
03-01-2011, 06:31 AM
First: Thank you for all the answers. They help this newb understand things a little better.

Second: With this new info.... is it advantagious (for maximized performance) to retard the cam timing, or is it best to be at TDC 0 Degrees??

Third: Are there any downsides to retarding/advancing the cam timing??

and...I think that I've found that Sticky at AT, so thanks for that. Haven't had a chance to read and reread it yet to full understanding.

In an ideal world you would want TDC 0 degrees. Some times you have to retard or advance them to get the propper draw length and such. It could also depend on the cam. From my experience on a bow that is a single cam I have found that if you cannot do TDC as you call it, it is better to have it advanced. The same goes for cams such as the NOS cams, CAT 1.5's or any cam with a lobe on it. Cams such as the CAT 2.0 or any cam that is lobeless I would say it would be of lesser importance. Also note I am basing my experrience on tunability and accuracy and not for maximum speed and such.
Others may have had different experiences so I can only base this on my experiences along with others who have validated my findings.

gstudt
03-01-2011, 07:02 AM
http://www.archerytalk.com/vb/showthread.php?t=626601

Here is the URL to the thread on AT.

I wonder who wrote it????

I'm just ready for "YKW" to post on this thread and tell you it doesn't matter just shoot your bow.

scepterman30x
03-01-2011, 07:04 AM
http://www.archerytalk.com/vb/showthread.php?t=626601

Here is the URL to the thread on AT.

I wonder who wrote it????
I'm just ready for "YKW" to post on this thread and tell you it doesn't matter just shoot your bow.

Duhhhh!:D:D

mudpig
03-01-2011, 10:12 AM
Just got done reading the AT sticky and all the other attached threads within. When I get home tonight, I'll take a look at my static cam position and see how wrapped up the cam is and make some adjustments and see what happens. I also want to play around with the draw stop to reduce the let-off and see what happens there. From the factory, let off was set at 80%. Draw length was set at 29 with the mod, but on the draw board it measures 29.5. To get back to a 29 DL, part of that can be done with the draw stop, AM I RIGHT? Should I twist the string, or does that counter act the cable twisting to wrap up the cams????

bfisher
03-01-2011, 11:30 AM
Yes, twisting the string will undo what you are doing with the cables. The net result, if you do both, is that you'll put more prebend on the limbs and increase the draw weight a bit.

Here's another one for thought. You can follow the path to optimizing the cam rotation, which will increase the draw length. If you wrap them both up 1/4" this should increase the draw by 1/2". Then your bow will be at 30". Put in the next smaller module and you're back down to 29". Give it a try.

Only problem I see with this is that wrapping the cams up tight is to produce more speed, but then dropping the module down you lose speed. It sounds almost like a wash to me, but then I've never done it so how would I know for sure.

Besides, my chrono bit the dust a couple years ago and I haven't replaced it. I got the sh!t's of chasing speed with a 27" draw. I get what I get. Shooting 3D I've had bows that shot 250fps, and I had one that shot 300fps and never missed a target because of lack of speed. Penetration on animals? I've blwn through with arrows hitting 280 fps and arrows shooting 180fps.

Brem
03-01-2011, 11:42 AM
barry,
When I did it on my Firecat I gained a few fps but mainly it reduced the noticable hump at the end of the draw cycle making it a little more pleasant to shoot.

mudpig
03-01-2011, 11:51 AM
Thanks fellas for all the help. Tonight after work I'll get my cams wrapped up and play with the draw stop/let off and report back.

Any other ideas out there??

copterdoc
03-01-2011, 12:43 PM
Advancing or retarding the cams, is something a bunch of people believe wholeheartedly, will allow them to find a "sweet spot", that allows them to achieve greater efficiency from their bow.

For the most part, it's a myth.

Changing cam timing, does a few things to effect speed. Sometimes, we fail to measure the "important stuff" that changes when we play with cam timing.

Things like brace height, draw length, and draw weight.

With Binary cams, like the CAT, Hybrix, and Nitro, it can even change the DFC, and holding weight.

However, while that "important stuff" effects speed, it doesn't do it by changing the bow's efficiency.

It changes how much energy you invest during the draw. If you put more in, you get more out.

A compound bow, is a machine. It's a simple machine.

copterdoc
03-01-2011, 12:47 PM
I only use them terms because the word 'retarded' gets banned. :confused:
Actually, that was my fault!:eek::D:eek:

bfisher
03-01-2011, 04:39 PM
Doc, what's DFC?

Also you're going to have a PM in a minute.

SonnyThomas
03-01-2011, 07:05 PM
Advancing or retarding the cams, is something a bunch of people believe wholeheartedly, will allow them to find a "sweet spot", that allows them to achieve greater efficiency from their bow.

For the most part, it's a myth.

A compound bow, is a machine. It's a simple machine.

I thought done in bold was better. Excellent reply, copterdoc.

As bf asked; DFC?

copterdoc
03-02-2011, 03:40 AM
Draw force curve.

Since each Binary cam actually has TWO cable tracks, they interact with each other, and effect DFC.

You only move or replace, one cable track (the module) on each cam, to change DL, however moving the draw stop changes where the cam stops at full draw.

Since the cam stops at a different point, the second cable track is able to effect the DFC. that's why you start to get a "hump" in the back end of the draw cycle on the CAT cam, if you set it at the top end of the module range.

By retarding the cams, and moving the modules to a shorter DL setting, you can still achieve the same DL as before, but you lose the "hump".

ElkSlayer
03-02-2011, 07:10 AM
excellent information from the Doc...again:cool: you should write a book on nos cam's my man

elkslayer4x5
03-02-2011, 09:10 AM
excellent information from the Doc...again:cool: you should write a book on nos cam's my man

I'll take a copy. :D

bfisher
03-02-2011, 06:27 PM
I have to admit that I missed reading Copterdoc's post explaining cam advancement or retardation. Sorry about that, but now I do have a better understanding of those terms. Thanks for that.

Scott, nice to see you around.

mudpig
03-03-2011, 06:13 PM
Okay, I did some adjusting over the last few evenings and got the cams wrapped up so that there is about 1/8th of an inch between my cable and the cable loop on both top and bottom cams. I ended up adding a twist and half to each cable and let out 3 twists on the string. My draw weight is dialed in perfect at 63# peak and adjusted my draw stop so that my total draw length was back down to just over 29". The hold weight came in at 20.5# which makes it 68% let off. This combination feels good to shoot and what did it do for speed?? It took my 380gr arrows from 285-288fps up to 300-303fps and my 390gr arrows are posting 295-298fps!!!

THANKS FOR ALL THE HELP FELLAS!!! Very happy with my SILENCER!!!:)

Brem
03-03-2011, 06:26 PM
mudpig,
that is exactly where I thought you should have been. Thats more like it, an IBO weight arrow in that bow will be doing 325 or better. Could you run one through the crono and let us know what it says?

mudpig
03-03-2011, 06:35 PM
I'll have to see if I can make something up that light. IBO weight would be 315gr, I believe. I'll let you know.

mudpig
03-03-2011, 07:08 PM
Brem, I just made up an arrow close to IBO. Lightest I could make up was 319.4gr. First arrow over the chrony was 330! But....shots after that were closer to 325fps :D

Brem
03-04-2011, 02:57 AM
"I feel the need, the need for speed". Fantastic

Nemesis03
04-09-2011, 12:25 PM
Not that I am not willing to give this a try but here are my concerns. Firstly, I used to own an '09 AX now a 2010 Nemesis and all info on these bows and cam systems were that anything less than equal cam sync at full draw will provide alot of shot noise and vibration so was/is this fact or falicy? Second, I have a Silencer on the way with seemingly the same cam system as the Ryteras, correct? So what gives? Is the Silencer loud and hard on the shot when tuned like the CATS? And does this work on the Ryteras with the same success?

SonnyThomas
04-09-2011, 03:09 PM
Not that I am not willing to give this a try but here are my concerns. Firstly, I used to own an '09 AX now a 2010 Nemesis and all info on these bows and cam systems were that anything less than equal cam sync at full draw will provide alot of shot noise and vibration so was/is this fact or falicy? Second, I have a Silencer on the way with seemingly the same cam system as the Ryteras, correct? So what gives? Is the Silencer loud and hard on the shot when tuned like the CATS? And does this work on the Ryteras with the same success?

To me " loud and hard" comes from a bow not tuned properly. Right now the noisiest thing on my Shadowcat is the draw cord for the Limb Driver - when it snaps tight to lower the rest after shot.

Nemesis03
04-11-2011, 03:19 PM
I'm catching on here but my only question is which is more important twisting the cables or untwisting the string or a combination? When do we know to employ one vs. the other or the combo.?

Nemesis03
04-11-2011, 03:26 PM
To me " loud and hard" comes from a bow not tuned properly. Right now the noisiest thing on my Shadowcat is the draw cord for the Limb Driver - when it snaps tight to lower the rest after shot.

I had my AX tuned w/cams in perfect sync. tiller equal and @ 28" if I remember correctly I was getting 312fps 61ish lbs. and I think a 315 grain arrow. The cams were not wrapped up or at least I did not concentrate on that while tuning. My current Nemesis is tuned the same way. I have not had a chance the chrono. it but both bows were/are WHISPER QUIET. I was just saying I was led to believe that unless the Hybrix cams were in perfect sync., your bow was not in tune so I find it interesting that some folks are saying that it does not really matter whether or not the space between the top and bottom cables and the mods. at full draw. I'm soakin' it up like a sponge.

Ehunter
04-11-2011, 04:38 PM
Is it possible to "over advance" the cams? I know you don't want the cables to touch the cable posts when wrapping up a cam, but can you get them too close? On my old '09 FC, I had them wrapped pretty close, and it shot like wildfire. Haven't tried wrapping my new FC400, but the Onza is wrapped tighter than the old FC. Cams are in time, but it seems a bit loud to me now. Just curious.

SonnyThomas
04-12-2011, 06:04 AM
This retarding and advancing the cams. Is there a sweet spot? I don't think so. Not unless you count fitting draw length. With the limb breakage Martin presently has we don't want more poundage, so forget twisting up the cables. When retarding or advancing the cams one should maintain ata.
Shorter draw; twist up bow string and let out the cables to maintain ata.
Longer draw; let out bow string and twist cables to maintain ata.

I just went through this with NOV RUT. The 2010 Shadowcat has a 41 1/2" ata. The too long a draw length measured 28 1/2". I twisted the string and cables as per NOV RUT and now have the deminsions of the 2011 Shadowcat, 41 1/4" ata (actual 41 5/16")and still have the too long of draw length of 28 1/2" and this with the mods set to 27". There is no more twisting up the bow string - It's over twisted now. How do you advance the cams? Let out the cables. To advance the cams to eliminate 1 1/2" of draw length makes the cams look incredibly wrong. And I'm still waiting for a reply from NOV RUT.
According to nuts&bolts this bow is correct for draw length. Incredibly advanced cams and incredibly wrong looking.

mudpig
04-12-2011, 10:02 AM
Those cams look rotated the wrong direction. Definately WRONG looking!!!

mudpig
04-12-2011, 10:09 AM
When I was wrapping my cams up....I was moving them the OTHER way. I was adding a couple of twists to the cables bring up to weight and untwisted the string to bring the cams around to where I wanted them. Then adjusted the draw stop to bring DL back into order. This dropped the let off, but for me was not an issue. Let off went from 80% to 68%. ATA is within a 3/32" and BH is within 1/8"

mudpig
04-12-2011, 10:52 AM
From reading threads here and at AT and working on my own two Silencers I have learned a bit about these. First, I believe it was Doc that said the magic number for cam pin to cable gap was about .070" Second, I think Archer said the first thing you should do is take cables and string off and make sure that they are at company spec lenghts (make them so). After that go slow, make an adustment and remeasure everything. After taking my string and cables to spec. I was under max draw weight with the limbs taken down tight. So, I added a twist to the cables and remeasured. Continued doing this until I hit max weight. I was still not close to the magic .070 so I let out the string a few twists to close the gap. I got my gap close (.09 top/.08 bottom). Then checked cam synch at full draw and draw length. The synch was spot on. If it hadn't been, I would take a 1/2 or full twist out of one cable or take up that much in the other cable to get the synch and not go over max weight. My draw length was way too long when I measured after wrapping up my cams. I shortened up my DL with the draw stop. Bringing it back down to where it needed to be while on the draw table. This REDUCED my let off to about 68% (down from 80%), and as a side note got rid of the really harsh bumb at the end of the draw. My ATA and BH are within 1/8" of spec. Both are on the long side of spec.