Let's Make Robots!

Building a multi servo robot

The parts arrived in the mail! Here they are:

I got 10 Turnigy TGY-S3101S servos, a Turnigy 15A max. UBEC, one 2S 1300mAh Turnigy LiPo and one 3S 1300mAh Turnigy Lipo (that I will use for my MiniEric robot).

Of course, I need to make servo brackets now and decide what I will build, a humanoid or an insectoid? Perhaps I'll start with a quad or hexapod and after I'll make brackets I'll take it apart and build a biped.

Oh, I am still waiting on the µServotino board to arrive. As soon as it gets here, I'll make a presentation page for it. 

I'll update with more pictures as the build goes on...

 

Update Dec. 26th 2010:

After a lot of research on the net to find something that little or no one has done before, I have decided to try my luck building a 12 DOF quad. I have found a model that will look interesting and started CAD-ing the parts to make the chassis and cover. The robot will have a completed finish, although I don't know yet if I'll use acrylic to make it or some light plywood (balsa?) and paint it afterwards. I remember somewhere that acrylic can be painted, since I have no idea where to find tinted acrylic sheet locally. Perhaps a nice metal paint job will make it look more "natural". I can have the parts cut out on a laser CNC at a local makershop, but I want to try to make them on my CNC first. Wish me good luck!

 

Update Feb. 21st 2011:

Finaly I got off and started to build a prototype. After a whole day of work in my closet (yeah, that's where I build stuff) I have something to play with until I'll get the proper acrylic parts cut. It took a lot of time to cut parts, drill, dremel, file and put them all together, take them apart to swap things around, make more wholes, try different stand-offs, solder battery connectors (I did not order mating terminals for the batteries). I thought it will never end. But there it was, all wires and wood sticks, ready to be programmed with the basics: center the servos, so I can put the horn screws in. But the green light did not shine. Ok, charge the battery. To my surprise, the charger said broken connection! I verify with the multimeter and the 7.4V battery was showing 3.9V... Uh-oh.... I measure the 3 pin balancing connector and on the red wire I got 3. something and on the blue wire I got 0.7V... I thought I should get a similar voltage to the red wire, as there are 2 cells in series... That means one of the cells is likely dead. Since I cut off the original connector, I can't return the battery, I'll have to order another one, this time with the proper connectors. Mean while, I removed the uBEC and the battery and replaced them with a regular 4 AA holder, but this just lets the servos jump a little at start and then it's all dead. Not enough current it seems... I'll try with different batteries tomorrow. And I'll take some pics, now it's late and I already connected half of the servos wrong...

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Hi Gonzik, thanks for the response. I could not see your link, it gives me an error. I was thinking to use balsa because it is light weight and I can easily cut it. The design has a lot of zig-zag lines that are just engraved in the material for the looks but also the edges of the parts are zig-zag-ed. The original design used large legs but I reduced the lengths so I don't stress too much the servos, I hope it'll be all right. I have to make some tests first and perhaps redesign. So the robot has a simple chassis then a cover shell that makes it look like a real thing. I'll cut out the chassis and legs first and do some tests then redesign the legs until they work properly, but I am taking into consideration your suggestion about keeping the middle link vertical (tibia?) although the original has it at an angle, but I suppose it is too stressful for the servos. I'm trying to figure out how to support the back of the servo rotation point, I see there are some rotation joints you can attach to the back of the servo, I need them for the hip rotation servo mostly. Do you happen to have code for moving the legs in Arduino? That would save a lot of testing time. The original model I'm following doesn't have a panning head, so I guess I'll just install a Sharp IR sensor in the front or just hide it behind the "face" panel. I don't have much space there at the moment, but I can figure out something after I'll have the first prototyping parts done. The leg design looks like the one on the Phoenix hexapod, but the femur servo is oriented with the rotation point upwards and the tibia is rounded the other way (slightly). Also, the tibia servo is mounted flat at the end of the hip servo, so the tibia comes out from farther from the hip joint.

 

Hard to describe the thing without revealing the real model or pictures. I just want it to be a nice surprise.

I am currently working on one. It's hidden from the robot pages but you can still find it at http://letsmakerobots.com/node/22460 . I used cheap servos...but what can you do. No money no Hitec =( My two points of advice would be to use LiPos (as I can see you are, I tried NiMH and they weren't good enough). Also make the legs similar to a spiders, in my design you can see the legs resemble a mammal more than an insect (this is because of the wheels) but if you are building purely a quad you want the joint angles to be as small as possible to put less pressure on the servos. Also make sure your legs line up perfectly center with respect to the "hip" servos (The ones that rotate the servo about an axis perpendicular to the ground). I would recommend acrylic over balsa. If I can offer any more advice feel free to ask!

For inspiration check out http://www.trossenrobotics.com/robot-kits.aspx and http://www.lynxmotion.com/