# Compound Bow Design



## Octabird (Feb 20, 2009)

Well first off it looks like a knock-off Hoyt, with the hand guard piece in front of the grip, which does not always accomodate all hand sizes, so you may or may not want to get rid of that. Also, on the top and bottom of your riser the limb pocket angle looks a bit too steep to me, but I have never made a bow myself. Keep in mind the limbs have to come back off the pocket and allow for compression and expansion to work properly. Most are not past parallel towards the grip, usually they are parallel or slightly above parallel, away from the grip. I believe the brace height factors into the limb angle and limb length, which allows for the bow to be more forgiving if you flench during your shot. Brace height between 6" and 8" is usually the norm.

Rest of it looks pretty cool, but kinda run-of-the-mill IMO. Maybe change up the slotted sections with a different design? Just my two cents, but cool none-the-less!

If I was incorrect in any of my assertions, I am sure the others will correct me, but this is what I have learned in shooting a bow over the last 3 years. Hope it helps...


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## Rick! (Aug 10, 2008)

Not a bad start. A couple of suggestions:
the applied forces for the analysis need the proper direction - the string is pulling the pulleys/cams mostly downward (and some in the draw direction) which means that the limbs are compressing into the limb pockets, or surfaces on your model.
two, use principal stress instead of von Mises - stuff breaks due to tension for the most part. Use 40ksi as the yield stress of a 6061T6 Al riser.
Make it lighter! it'll do two things; it will make its first modal frequency higher which is good, and it'll be easier to haul up and down a mountian. look at the Mathews Heli(m) for light ideas for stiffness.

Good work so far, keep us updated.


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## isaacdahl (Feb 27, 2010)

Looks like a good start.

One thing I can add is that 3/4" thickness is almost standard for most bows out there...looks like you have quite a bit on that.


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## cncjerry (Jun 28, 2011)

there was another person on here that was a cad student in highschool working with Catia. search for that person's posts since there was a lot of good stuff in there.

I've been selling or managing the sales of Catia for almost 30yrs and never saw it in a highschool until the other person posted.

Jerry


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## spazzcdnm (Nov 4, 2010)

Rick! said:


> Not a bad start. A couple of suggestions:
> the applied forces for the analysis need the proper direction - the string is pulling the pulleys/cams mostly downward (and some in the draw direction) which means that the limbs are compressing into the limb pockets, or surfaces on your model.
> two, use principal stress instead of von Mises - stuff breaks due to tension for the most part. Use 40ksi as the yield stress of a 6061T6 Al riser.
> Make it lighter! it'll do two things; it will make its first modal frequency higher which is good, and it'll be easier to haul up and down a mountian. look at the Mathews Heli(m) for light ideas for stiffness.
> ...


I agree with the application of forces needing to be changed, but its important to realize that depending on the design of the limb pockets. Usually the are compressive forces on the inside of the riser, (an easy example is the pivot of a center pivot designed bow) and there are tensile forces acting on the other foreward part of the riser (where the limb pocket is RETAINING the limbs. ex: The Anchoring extention of a center pivot riser) So you would have forces being applied almost normal to the riser at the limb pockets in tension and compression.


Also, take sight mounting and stabilization into consideration. The riser needs to be tapped for it, and I dont see anything there. Otherwise it looks like a great start. Keep with it, CAD is an excellent skill to have!


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## thscad (Feb 2, 2012)

ya me and thscadstudent are in the same class. haha its awesome that we are offered catia in high school!


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## Bowtastic (May 8, 2012)

Truthfully, I feel that the overall build of the bow is very low-quality.


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## Mig (Nov 26, 2008)

Bowtastic said:


> Truthfully, I feel that the overall build of the bow is very low-quality.


Not to sound like an jerk but these guys most likely never shot a bow before or may have a little experience but I think it looks great. Especially if he only went off pictures. Yes, it does look similar to a hoyt, but sometimes the best things for a student to do in order to learn how to use any CAD software is to reverse engineer something. That's how I learned. I took apart things and modeled them. My teacher was a moron and was asking students how to do certain things in inventor. I never got to do any of this in highschool. I did everything in college.


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## cncjerry (Jun 28, 2011)

Bowtastic, is this what the future bodes for you? Your first post is a criticism? 

Were you installing the most expensive and complicated CAD system known to man, that is used to design fighter jets and Ferrari F1 cars, and designing a bow in highschool? Doing VM stress analysis as well?


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## pacnate (Sep 23, 2009)

Bowtastic said:


> Truthfully, I feel that the overall build of the bow is very low-quality.



Nice first post there bud!

To the original poster....Looks like you have a good start. I don't know much about all this, but sounds like you have gotten some good advice prior to this. Listen to these guys. Most of them know what they're talking about....I guess...lol.

Have a blessed day!


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## cncjerry (Jun 28, 2011)

Ths, I don't think you have the force vectors on the riser ends correct. Draw a sketch of the limbs then a triangle representing the string with a draw length of 28". You will be able to see the correct angle better. I think the limb mount actually has opposing vectors based on the pivot but clearly a net down + back force vector. If I were your teacher I would suggest you split the surface around the grip so you can apply the force against a surface that models your grip contact.


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## onyx48166 (Feb 9, 2011)

I'm the lucky one that gets to have talented students in class. These guys "thscad" and "thscadstudent" are both my students in high school. I think they are doing great work for high school students. I'm loving every minute of being part of the future they will have in the design industry.

Thanks for ALL THE POSITIVE feedback guys.


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## Mig (Nov 26, 2008)

onyx48166 said:


> I'm the lucky one that gets to have talented students in class. These guys "thscad" and "thscadstudent" are both my students in high school. I think they are doing great work for high school students. I'm loving every minute of being part of the future they will have in the design industry.
> 
> Thanks for ALL THE POSITIVE feedback guys.


I wish I had someone like onyx as a teacher, and in highschool. We didn't have anything like this in my highschool but I wish I did. these students will be one step ahead if they take any CAD classes at a college level. Kids at my school could test out of the class and actually move ahead of everybody and take additional classes. Plus, I couldn't design any hunting equipment. I tried to a gun, but that was a no no. Not even a BOW. I did a quantum spincast fishing reel. Animation worked and everything.


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## nuts&bolts (Mar 25, 2005)

thscad said:


> ya me and thscadstudent are in the same class. haha its awesome that we are offered catia in high school!


Hello thscad:

Excellent first effort.

FOLKS need to remember that you are in HIGH SCHOOL.

The curved brace needs to allow room for a human wrist, and forearm in the grip area,
so you probably want to flare the brace sideways.


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## nuts&bolts (Mar 25, 2005)

onyx48166 said:


> I'm the lucky one that gets to have talented students in class. These guys "thscad" and "thscadstudent" are both my students in high school. I think they are doing great work for high school students. I'm loving every minute of being part of the future they will have in the design industry.
> 
> Thanks for ALL THE POSITIVE feedback guys.


Hello onyx48166:

You are doing a GREAT job with your students.


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## Bean Burrito (Apr 20, 2011)

Just a few things I can see...

-Grip would be better down the centreline of the bow
-You've modelled your forces incorrectly; have a look at some existing bows to figure out where your vectors would be. If you need help send me a PM and I'll do a drawing for you
-Weight; your cut outs and pattern are good, once you've done some more simulations I'd thin it up in a few areas
-Your berger holes (the two larger holes) need to be closer to your grip, and you need the two (or more) holes for sight mounting
-Bow could use more of an arrow shelf
-Cost: try design your bow so it can be machined from an extrusion, with a minimal number of tool changes, preferably only in 3 axis also

Otherwise, you're doing very well. I'll upload a photo in a minute of some changes that could be made


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## nuts&bolts (Mar 25, 2005)

Maitland Zeus.











Maitland Zeus raw riser undergoing CNC machining.










http://www.youtube.com/watch?v=YGOsGMz0aH4&feature=player_embedded#!

Fascinating to watch.


First thing I notice, in the Maitland riser,
is the symmetry.


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## Bean Burrito (Apr 20, 2011)

I missed the force vectors for the grip but I'm sure you know how to add them


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## nuts&bolts (Mar 25, 2005)

RED ARROW is the sight windoow.


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## nuts&bolts (Mar 25, 2005)

Bean Burrito said:


> I missed the force vectors for the grip but I'm sure you know how to add them


Sight mounting holes need to be vertical.


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## Bean Burrito (Apr 20, 2011)

If you look at the two small yellow circles with the arrows going to them, they are 

The other box and arrow shows where the berger holes need to be moved to


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## nuts&bolts (Mar 25, 2005)

Bean Burrito said:


> If you look at the two small yellow circles with the arrows going to them, they are
> 
> The other box and arrow shows where the berger holes need to be moved to


Ok.

Thought the two large holes looked like berger holes.


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## Bean Burrito (Apr 20, 2011)

nuts&bolts said:


> Ok.
> 
> Thought the two large holes looked like berger holes.


I think they're meant to be, maybe this riser is made for some revolutionary new arrow rest? :darkbeer:


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## thscadstudent (May 4, 2012)

Thanks for all the the feedback everyone! I'm trying to incorporate all your suggestions and I will post those pictures as soon as I am done.


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## TailChaser (Aug 13, 2005)

What nuts and bolts said. I'll add if you really want to do it well, it's overbuilt in many places and you could shed a lot of weight. There's more, but that would do pretty good for a HS student. If you made it your own design and more original, it would be more impressive to the teacher. Check out the alien bows for example, or APA bows for a few ideas.


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## shaffer88 (Dec 3, 2007)

I can't add any info tp what already has been stated, but I will say this if this becomes a target bow please paint it the same as your finite element analysis view would be cool looking

Sent from my DROIDX using Tapatalk 2


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## thscadstudent (May 4, 2012)

Is this the correct way to apply the forces?


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## isaacdahl (Feb 27, 2010)

In one of bean burrito's post he shows some pics of how the pressure is distributed. That should give you a good idea. Nuts&bolts or bean burrito can explain it better than I can, but some of the limb forces are opposite of what you have them.


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## Bean Burrito (Apr 20, 2011)

Hi Cadstudent

Here's how I'd explain the limb pocket forces

get a ruler, and place about 3" sitting on a desk. Use your finger to support the end. Now, place your thumb under the end of the ruler (about 3" away from the end) so your thumb sits between the ruler and desk, and your index finger sits over the ruler. Now, push the end hanging off the table (the opposite end) down a little. This represents the tension in the cables. You should now be able to feel where you should model forces very easily. (your index finger represents the limb bolt, and your thumb the back of the limb pocket. The hand you push down on the other end with the ruler is the tension in the cables from preload and drawing the bow).


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## thscadstudent (May 4, 2012)

I just did your ruler example and I completely understand your picture now. Thank you


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## thscadstudent (May 4, 2012)

Hi all,

My class is almost over for the summer so I posted my final pictures of the bow on a different thread. The other 2 bows are my 2 classmates so you can vote for your favorite on there because we are trying to see the overall favorite. Here is the link... http://www.archerytalk.com/vb/showthread.php?t=1769088. Thanks


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## Thansen (Sep 23, 2009)

Another good one to watch. Listen to these people on here and they will give you good advice. These people will teach you alot. I do all my own bow work but have never built one so I'm going to follow this and learn as well. Looks good so far would love to see finished bow so keep posting progress.


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## Big_country09 (Aug 11, 2011)

I love the idea you guys have about designing a bow! i just recently signed up for computer aided design at university here and that was my dream to design my own compound bow. Just the thought of taking a beautiful whitetail with something i designed and manufactured on my own is just extraordinary. Keep up the good work and dont stop doing this if its what you like. no matter what you do with this you'll always have at least one bad critic. i think it looks great just keep up good work


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