Saturday, May 26, 2012

Dogbot: Openscad vs. Solidworks

This is a tough post for me to write because I am still processing a decision I need to make. Hopefully this post will help me, as well as you.

First, a little background. I started work on a dog robot a few years ago. One key aspect of the design was the solid bits that I printed on my 3d printer, which connected the servos together and gave the robot a shape. I chose to use a tool called Openscad  to design these parts. Because I kept the parts simple I was able to design them with Openscad fairly easily. I was even able to animate them to verify that I got the math right. All of this work is on my youtube channel.

Now here is where the story gets interesting. As I start to add in sensors and finalize the design I am desiring a much more complex design. I am wanting a design that can be considered to be art as much as good engineering. As I design artistic and life resembling parts I am starting to feel like I have reached the limits of Openscad. I don't give up without a fight, however. Here is an animation of my last stand:



This leg took me at least 10 hours to design and I was mentally fried multiple times by trying to visualize while I coded. In fact, I frequently picked up a pencil and paper as a faster medium to work out the kinks in my design before changing code. This is not how I want to design. I want my tools to be inspiring and suggestive, not tiring. Maybe I am doing something wrong. To give you a better idea of how I designed the lower portion of the leg, here is the code:

module leg_lower(){
difference(){
union(){
difference(){
translate([leg_upper_length/2,0,-servo_h+3])
scale([2,1,1])scale([1.3,1.3,2])
cylinder(r=leg_upper_length/2,h=servo_h/2, $fn=1000);
translate([leg_upper_length/2,0,-servo_h+3-1])
scale([2,1,1])scale([1.2,1.2,2.1])
cylinder(r=leg_upper_length/2,h=servo_h/2, $fn=1000);
rotate([0,15,0])translate([-500,-500,-servo_h+3+servo_h-0.1])
cube([1000,1000,100]);
translate([-500,0,-50])
cube([1000,1000,100]);
rotate([0,0,-45])translate([-500,45,-50])
cube([1000,1000,100]);
translate([leg_lower_length+5,-35,-servo_h+3+servo_h/4])
rotate([0,0,35])rotate([90,0,0])cylinder(r=screw_r,h=100,center=true,$fn=100);
}
translate([leg_lower_length-18,-26,-servo_h+5+servo_h/4])
cylinder(r=5,h=servo_h/2+4,center=true,$fn=100);
}
translate([leg_lower_length-18,-26,-servo_h+5+servo_h/4])
cylinder(r=2,h=servo_h/2+4+1,center=true,$fn=100);
translate([leg_lower_length-18+5,-26,-servo_h+5+servo_h/4+0])
rotate([0,0,25])cube([1,5,20]);
translate([leg_lower_length-18+5,-26,-servo_h+5+servo_h/4-20-3])
rotate([0,0,25])cube([1,5,20]);
translate([leg_lower_length-18+5,-26,-servo_h+5+servo_h/4+0])
rotate([0,0,25+180])translate([-1,-5-5,0])cube([20,15,5]);
translate([leg_lower_length-18+5,-26,-servo_h+5+servo_h/4-5-3])
rotate([0,0,25+180])translate([-1,-5-5,0])cube([20,15,5]);
}
}


Does it make sense to you? What line of code makes the screw hole that holds the rubber ball to the leg? Even after writing it I couldn't tell you right away.

After this experience I started looking for a new tool. I am not a mechanical engineer. I didn't know what to use. So I started looking around the internet for something that looked like the best CAD tool out there. I found a few, but Solidworks stood out as a FUN tool. I want to have fun!

So I decided to conduct an experiment. Below is a picture of a servo that I use in my dogbot. What would the experience be like modeling this servo in Openscad? What would be the experience modeling it in Solidworks?


To model this in Openscad you need to keep it simple. Here is the code to create a rough representation of the servo:



module servo(){
color([0.6,0.6,0.6])union(){
//drive shaft
translate([0,0,-servo_ds_h])
cylinder(r=servo_ds_r, h=servo_ds_h);
//body
translate([-servo_t/2,-servo_t/2,-servo_h-servo_ds_h])
cube([servo_w,servo_t,servo_h]);
//flange
translate([-servo_t/2-servo_flange_l,-servo_t/2,-servo_h+servo_flange_z-servo_ds_h])
cube([servo_flange_w,servo_t,servo_flange_h]);
//wire
translate([-servo_t/2-servo_wire_l,-servo_wire_t/2,-servo_h-servo_ds_h])
cube([servo_wire_l,servo_wire_t,servo_wire_h]);
}
}


It only took me about 30 minutes to get the code just right and to take all the measurements. Here is a render of the result:



So next I tried to design this servo in Solidworks. This was one of the first times I have used Solidworks after watching a few youtube tutorials. At first I just went with a simple representation like I did with Openscad, but that only took 10 minutes. So I decided to see how far a newbie could take it. I buckled in and took it all the way to what I consider to be an identical representation. In less than 2 hours I finished the design! In another 30 minutes I had the material tools and rendering tools figured out. Here is the result!


If you put the original servo next to this render you can barely tell them apart, and that's just because I am new to Solidworks. So now I have a dilemma. Openscad is open source and I believe in open source. It is code based and because of this you can create parametric designs that can change by changing one variable, like bolt size. Solidworks is hundreds of dollars and is almost completely mouse driven. But Solidworks is fun and almost without limitless with a new version is coming out every year.

What to do? Which do I use? Is there something even better?

11 comments:

  1. If I could afford to get it I would like to try something like Solidworks. One of the problems I have with openSCAD is the same as you said, it is hard to visualise the design with code. I also don't like that it decides how many facets to put on curved objects, they tend to show once I have printed out. As a hobby I would say go with what gives you the greatest pleasure while meeting the design needs you have. It is a hobby and meant to be enjoyable, at the point it isn't; open/closed source becomes mute as you wouldn't carry on with it.

    ReplyDelete
    Replies
    1. Somewhat OT. Do you know about $fn, $fs, and $fa? I usually use $fn=90 to make decent looking circles/cylinders on screen. I am sure I could go further, if I thought it would make better printed parts.

      Delete
  2. Hmmmm... tempted you are. The first step to the Dark Side temptation is. ;)

    Kidding aside:
    I was very thrilled by your skills with Openscad but your Servo made with Solidworks looks just stunning. Is it already that you don't enjoy Openscad like you did before? Like smartroad said: It has to be fun so that it could go on.

    Very difficult choice!

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  3. My vote is to go with a solid modeling program. Being able to run renders and check part interferences in large complicated designs is amazing. Plus the parametric nature of most solid modeling programs lets you make quick iterations and see how the effect the overall assembly. I have nothing against OpenSCAD and started off that way as well but my designing work (both personal and commercial) has become far far more efficient since I moved to a full 3D solid modeling program.

    Sadly the good options are usually costly and closed source, thats my only negative I can put towards them.

    ReplyDelete
  4. Somewhat more on topic. WRT mystery code, there is nothing that says you have to code just cubes and cylinders inside your difference/union/translate functions. You could break them into smaller modules, especially if they get reused, or, if they are a difference to break out a part from a cube/cylinder. I was going to point to my 4" impeller on Thingiverse, but, it would seem that is much earlier work, and, looks a lot like your "where is it" code above. :)
    http://www.thingiverse.com/thing:15370 in case you care.

    ReplyDelete
  5. Thanks for all the feedback and advice. After thinking it over and considering these comments I've decided to go with Solidworks. Openscad is an amazing tool and it has a justified place in the opensource community. I am going with Solidworks because I have limited time for my hobbies and when I have the time to work on them I want to have the most fun that I can and accomplish as much as I can. Thanks again for all the feedback!

    ReplyDelete
  6. Maybe consider FreeCAD? It seems to have a lot of potential.
    I also like Kyle Kerr's point, by breaking it up into multiple module's with names that make sense you can make your code/model more readable. Just like it makes sense to use proper function/class names when you program.
    .

    ReplyDelete
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  8. These are really good and better to contribute more on the robotics part. Well made with Openscad. The robot work Looks stunning indeed. Check this out Generic Viagra

    ReplyDelete
  9. Well, here is one hour in OpenSCAD got me: http://imgur.com/a/ExDjs

    Here's the code that got me there (again, that's one hour).
    Not the best code by far, but at least it's clear how to change the dimensions of sub-parts.

    //coded in <1hr in response to http://www.onshoulders.org/2012/05/dogbot-openscad-vs-solidworks.html
    //romwell@gmail.com

    L=50; //length
    W=22; //width
    H=45; //height
    A=15; //main slope
    r=3; //hole radius
    t=3; //thicknes of holders
    w=8; //width of holders
    k=0.68; //hole position ratio
    d=3; //distance of holders to slope end

    br1=0.8*W/2; //button base big R
    br2=0.75*W/2; //smaller R
    bh1=2.5; //cone height

    bh3=0.2; //button base deco circle
    br3=0.9*br2;

    br4=4.5; //BUTTON RADIUS
    bh4=8; //BUTTON HEIGHT

    br5=br4/2; //button hole radius

    B=L/2.3; //small box length
    hh=1; //bevel amount
    sr=2; //decorative circle radius
    SC=0.9; //smaller box slope cut off
    AA=75; //smaller box slope angle

    module slopebox(w, l, h, d, a)
    {
    difference()
    {
    cube([w,l,h]); //main box
    translate([-1,d,h])
    rotate([-a,0,0])
    cube([w+2,l+h,l]); //slope
    }
    }

    module wire_holder()
    {
    difference()
    {
    cube([W,w,t]);
    for(x=[W*0.25, W*0.75])
    {
    translate([x, k*w, -t])
    cylinder(3*t, r, r, $fn=24);
    }
    }
    }

    module bbox()
    {
    k=0.9;
    kk=(1-k)/2;
    C=SC*B;

    k2=(k - k*k)/2;
    difference()
    {
    union()
    {
    translate([kk*W,0,0])
    {
    slopebox(k*W,B,S+hh,C,AA);
    translate([k*W/2,0,S])
    cylinder(hh,sr,sr,$fn=24);
    }
    }

    translate([k2*W+kk*W,kk*B,S])
    {
    cube([k*k*W,k*C,2*hh]);
    }

    }
    }

    module but()
    {
    difference()
    {
    union(){
    cylinder(bh1,br1,br2);
    translate([0,0,bh1])
    cylinder(bh3,br3,br3);
    }
    cylinder(100,br4*1.1,br4*1.1);
    }
    difference()
    {
    cylinder(bh4, br4, br4, $fn=60);
    translate([0,0,bh4/2])
    cylinder(bh4, br5, br5,$fn=24);
    }
    }

    module butbase()
    {
    k=0.95;
    bbw=k*W;
    t=(W-bbw)/2;
    translate([t, t, 0])
    difference()
    {
    cube([bbw, k*L/2, hh]);
    translate([bbw/2, L/2-t, 0])
    cylinder(2*hh, sr*1.3,sr*1.3, $fn=24);
    }
    }

    slopebox(W,L,H,L/2,A);
    S=L*sin(A)/2;
    translate([0,0,H-S])
    {
    translate([0,L/2,0])
    {
    bbox();
    }
    //wire holders
    translate([0,0,-d-t])
    {
    translate([0,L,0])
    {
    wire_holder();
    }
    mirror([0,1,0])
    wire_holder();
    }
    }
    translate([0,0,H])
    {
    butbase();
    translate([W/2, W/2, hh])
    {
    but();
    }
    }

    ReplyDelete