New Quad Project... INPUT VERY WELCOME!

km6vv · July 17, 2011, 2:36am

Yeah, that came out a little funny.

Which way do the treads face? I assume they have to stay parallel? Can you rotate the legs enough to get 90 degrees? Maybe you just walk on toe tips?

Alan KM6VV

marcham · July 19, 2011, 12:00am

I think I see what you’re asking. The legs, while walking, will default at 90 degrees from each adjacent leg. While in rolling mode the legs on either side will be parallel to each other. If you look at the pictures in my first post that might illustrate it a little better.

Is this what you’re asking? I seem to be a little thick lately.

km6vv · July 19, 2011, 1:00am

Yeah, I think that’s it. I could see it after I looked again. Long day!

Alan KM6VV

marcham · July 19, 2011, 3:35am

I hear that.

andrewrobotics · July 20, 2011, 2:40pm

Hi Marcham,
this idea is brilliant … I’m curious to see the robot complete!
Good job and good luck!

dialfonzo · July 20, 2011, 3:10pm

Hi Marcham,

I see in you CAD drawing that you include a solid Tibia between the two tracks.
Did you dumb that ?
I do think it’s good idea to have it.

Eric

marcham · July 20, 2011, 7:31pm

Thanks Andrew!

Eric, that spreader will be there. The holes are in the leg for it but I just haven’t machined it yet.

cdraptor · August 3, 2011, 2:38am

Just checking to see if Marcham had any updates on progress of his new Quad

marcham · August 3, 2011, 2:29pm

Hey,

It’s been a while. I’ve been working on programming lately. I’ve got the IK worked out for joint angles and I’m working on a gait engine at the moment.

I’m using the equation for an ellipse to determine foot trajectories: The major and minor diameters being the step length and height. Body shifting will be sinusoidal. The amount of body shift is determined by the coefficient of the sine term.

I’ve got a new spindle so I will probably do a lot of machining next week.

I need to make my controller!

I need to finish my vacuum fixture for my mill.

I need to get my brakes checked.

So much to do.

So many non sequiturs.

marcham · September 22, 2011, 4:54am

Hi guys,

I’ve been putting a lot of work into this lately, but not too much to literally show for it.

Through my machining endeavors I’ve ran into quite a few problems. The CAM software I had been using, meshCAM, while simple to use is not very powerful. I am basically left to be satisfied with whatever tool path it automatically creates. Sometimes it doesn’t complete the part fully, it doesn’t handle gradients well, it skews some proportions of parts while doing other correct leaving me with parts that are half correct but still not acceptable. So, I’ve invested quite a bit of time teaching myself mastercam. We have a license at work which I can use over VPN. The short of it is: I LOVE IT!

I’ve also revised quite a bit of my quad design. I’ve finalized the turret assembly, and changed the body. I’m also still working on revising the tars/track assembly. The first version is too complicated. I’m working on reducing the number of parts and making it more solid and clean.

Anyways, thats what I’ve been up to. I’ll leave you guys with a pic

dialfonzo · September 22, 2011, 11:31am

Nice…

Good to have some info on it.
Still like it a lot.

Keep your good work.

roboted · September 22, 2011, 4:31pm

Marcham,

I really like the redesign. You have retained the beveled edges which give the whole thing a very polished, finished look. The “housings” for the coxa servos, much like molded shield surfaces on a fighing machine, really improve the overall appearance.

I notice you flipped the femurs vertically. Does that improve clearance, maneuverability, or both? Do you have a picture of it in “tank position” similar to “Roll.jpg” in your first post? Also the blue rods where the feet used to be; are you replacing the feet with rods, or are they simply place-holders in your drawings to be replaced with revised feet later?

You can probably tell I remain very interested in this project. It is complicated but intriguing.

marcham · September 22, 2011, 5:40pm

Thanks guys!

Yes, I flipped the femurs to reduce the chance of interference. It seems like it will be more helpful in the tank position, I’ll post a pic when I get home from work.

I do plan on replacing the feet with 3mm hardened steel rods then probably try to find a rubber tip to place on the ends. The length of the feet would be too long for the epoxy resin material I would have used: too much deflection.

I hope to have the foot assembly revised soon. I’ve got the idea in my head I just need to put it into solidworks and confirm its feasibility.

dialfonzo · September 22, 2011, 5:52pm

(Need my CNC … LOL)

marcham · September 23, 2011, 4:26am

Took a while but, as promised, here’s the pic of the tank configuration.

And, Alan, your question before:

I think I finally understand what you meant. No, I can’t get the legs to be 90 degrees from each adjacent leg. So a zero point turn like that would not be possible. It is pretty close though. When I have it assembled I will have to see if is able to do a skid turn like that.

Edit: Ha, maybe I still don’t fully understand . If what you were asking is if it will be a full time skid steer system then the answer is no. I plan to use the rotation of the coxa to steer it in tank mode. The tracks won’t stay parallel but they will remain tangent to concentric turning circles focused at a common point.

roboted · September 24, 2011, 6:10pm

Marcham,

I really like your latest post with the tank.png picture. This thing is really looking good.

If I may, I would like to offer a few thoughts, not as criticism because I don’t know enough to be critical:

I notice that this configuration places a great deal of tread on the ground where it could create a lot of friction to overcome and possibly some tread wear.
If your “ankle” servos offer enough rotation, you may be able relieve most of the friction and stress most of the time by rotating the “toe” ends of the treads further upward so that ground contact is concentrated on the road wheels currently pointed to by the ends of the femurs. This would still allow you to use full tread contact in dusty, soft, or slippery surfaces.

I certainly am not suggesting any sort of redesign because I love what you’ve done. But since you are working with a tracked vehicle, I thought you might be interested in an exchange I had in March 2009 on the Lets Make Robots Forum with a former tank driver signed Cwignell. On that forum I was TechnoBuff until my brother envisioned me doing technology in the buff.

My very best wishes to you, RoboTed

//////////////////////////////////////////////////////////////////////////////////////////////////////////////

Everything that follows is from the LMR Forum. Snailkeeper correct me if I’m doing this wrong.

Track design for tracked robots
By TechnoBuff

March 11, 2009
I am brand new to the robot hobby with questions about track profiles.

The high sided triangular track profile of Wall-E or Johnny 5 looks really good, but seems to make inefficient use of track links. Other than good looks, is there a good design reason for this profile?

Of the other general profiles available (parallelogram - WWI tanks), (rounded rectangle - Christie type WWII tanks), (inverted trapezoid - short base down), what are the relative merits in terms of efficient use of links vs. object climbing ability?

Of these, which tend to cause the most stress on the links, and which cause the least?

Thank you for your assistance.

By cwignell
@ Wed, 2009-03-11 10:04
Hi TechnoBuf,

You will see the Wall-E arrangement on BullDozers, it has the advantage the it puts the final drives closer to the middle of the vehicle and having the drive sprocket higher means the track tend to self clear rocks and crap which you can pick up when turning; this reduces thrown tracks.

The rombod tanks from WW1 were designed around the minimum radius wheel which would cross the trenches then in use.

The convential approach with the drive at one end at a similar level to the idlers puts the powerplant and transmission at one end of the vehicle (usually the rear) and leaves a big crew space (well it’s not, it’s very snug because there is a lot of stuff in there with you.). This also serves to lower the profile, handy went people are shooting at you. Picking up rocks is less of an issue with the modern tank but if you look closely at some of them they have plow like arrangements to clear the tracks before the sprockets.

As for climbing, the convential approach is the best normally you can get up verticle steps a little bigger than the height from the ground to the front idler/sprocket. The max gradent depends on a lot of things, Hp, transmission, traction, surface and so on.

The Wall-E arrangement will have a poor step performance, and step performance is not a big issue for bulldozers.

Oh if your wondering, I drove tanks for a living once.

By TechnoBuff
@ Fri, 2009-03-13 23:43

Thanks, Cwignell,

Excellent answers concisely stated. Wall-E design now makes sense where CG considerations require driven sproket near center and climbing is minor design factor. Your comment on climbing is very encouraging. I had expected top sprocket would have to loom over step height rather than possibly being slightly below. A clarification question: When you described “conventional approach”, I envision a Christie-like design but with the front and rear end wheels raised somewhat above the level of the ground contact base wheels and idlers guiding the tread on the return direction. This would give a little more climbing ability than an absolutely flat arrangement like some cranes and road paving equipment. Did I understand you correctly?

Re you last sentence, since you answered my inquiry, I assume “living” was the operative word. Good!

TechnoBuff

By cwignell
@ Sat, 2009-03-14 02:20
Hello TechnoBulff

Yes when if refer to to convertional approach I mean where the leading wheel is raised and the the rear wheel is raised and all of the Roadwheels sit on the ground, note, the leading and read wheel can be either the driven (sprocket) or an Idler. The trend with moden tanks is the rears are the drives as it allows all of the engine and transmission to be incapsulated at the rear, but there are some front drive tanks around. Speed and mobility on the modern battle field are important, climbing ramparts (steps) and trenches is not so important any more.

To be strictly accurate Christie like design refers to a convential approach as above, but uses large diameter roadwheels on a swing arm suspension, the Russion T-34 and the English Crusaider were early examples of this. The robot I am building at the moment is basically a Christie design. Christies were optimised for speed and some of them could be driven with out tracks. Track wear is still an expensive issue with tracked machines.

Regarding getting up steps, the actual height you can climb depends on the geometry of the step, the type of surface before, available traction, torque available and if the driver is willing to break the vechicle! One upper limit to step type obsticles is the Height of the Center of gravity vs wheelbase vs step height. Tracked vehicles can assum alarming attitudes.

marcham · September 24, 2011, 10:59pm

Hey, Roboted. Thanks for the thoughts and info.

You’re right. The amount of tread on the ground and their distances from the center of the bot would make skid steering very difficult. Honestly, with the motors that I’ve chosen to do this with it probably wouldn’t even be possible. The way I’ve planned to steer should eliminate most of the lateral forces on the treads. This picture shows a top view of the robot mid turn.

So, as you can see, the treads actually turn, making considerations very different from the typical tracked setup.

I’ve thought about rotating the tracks a bit in some cases to reduce the amount of ground contact. However, in the case of skid steering I think it would make matters worse. Regardless of the amount of ground contact the friction force would remain the same. Friction force depends only on weight and the coefficient of friction, surface area isn’t a factor. So in this case, it seems that rotating the tracks towards the driving wheel would localize the friction forces farther from the robot center making the moment from friction larger.

As for wearing, reducing the amount of contact might make that worse, too. Putting greater strains on a smaller section of track could eat them away faster.

I really do appreciate the input. I knew starting this out that there would probably be things that I would overlook. So, I’m happy that you pointed this out, it’s good to actually make me think and justify the decisions I made.

km6vv · September 25, 2011, 5:56pm

It will be interesting to see the video when you get it working!

I like the tracks.

Alan KM6VV

keyboard · January 19, 2012, 5:19pm

Awesome project when it is done could you be so kind as to let us normal roboters see the technical designs and coding to be able to make one our selfs

Thaks

marcham · September 7, 2012, 12:07am

I’m Back!

I can’t believe my last post was almost a year ago. I may have been gone, but I’ve been busy.

I realized a while ago that part making process I was using wasn’t going to give me the robot I wanted. I revised my design to try and use G10 but that wasn’t really cutting it. Then I stumbled on this guide on resin casting: lcamtuf.coredump.cx/gcnc. From then I figured resin casting was the way to go.

I’ve spent the last 4 or 5 months slowly stocking my closet machine shop with the materials and tools I needed. I learned some new CAM software and did quite a bit of trial and error machining runs to hone my programs. I finally got to a point where I could hold a tolerance within about 0.01mm. I’ve completely redesigned my quad to be produced with casting and have recently been making the molds to cast my parts. Today, I finished my first leg prototype. Here’s a couple washed out photos of the leg and another of one of the mold positives and its resulting negative.

I think it turned out decent. The parts fit well with only a few modifications and different screws needed. I haven’t quite perfected the actual casting process so some of the parts came out a little rough around the edges. The pinkish parts were really supposed to be a darker red color but I apparently bought the wrong pigment. I’ve got a few others ordered to play around with. Also, these aren’t just pure polyurethane, they’re filled with glass fiber and glass microspheres to increase rigidity and decrease weight. I treated the fillers with a silane coupler to promote adhesion with the resin and further enhance it’s mechanical properties. I still need to play around with the proportions to strike a good balance of weight, rigidity and impact strength.

In the coming weeks I’m planning on making the necessary modifications to my molds and refining my casting process. Hopefully I’ll have this all worked out soon, then I’ll start machining molds for the body.