Bing 3

[DerekZahn]

Merry Christmas everybody! While waiting for Santa I got in some quality Bing time. Here's the two ankle pods, wired up and with a batch of freshly-baked microcontroller code. They communicate successfully with my very rudimentary PC-based monitor program.



bigger: http://happyrobots.com/bing3s.jpg

Here's a few shots illustrating some of how the wiring gets routed. Some flanged plastic bushings get a groove cut in them for an eventual e-clip and then get put into bearings:



bigger: http://happyrobots.com/bing3t.jpg

Here's the bearings pressed into the mounting plates:



bigger: http://happyrobots.com/bing3u.jpg

And finally the whole thing bolted into place:



bigger: http://happyrobots.com/bing3v.jpg

[djmartins]

I must say, nice work.

Please keep posting even of you get few replies as I am sure many are left speechless!

regards!

[Dimitris]

Wow! Very detailed and professional work! I like! Please keep posting as it progresses! Best of luck!

[DerekZahn]

Thanks guys! I can tell from the numbers that some people are reading; I don't really expect a lot of comments... I just know how much pleasure I have gotten from reading reports from the Japanese Robo-One builders and hope that others can get a little fun from seeing what I'm up to.

Even though I try to find bargains where I can (you can get the HSR-5995TG servos for $90 - $95 on Ebay and also cheap bearings, plus I have a plastics shop nearby that sells scrap Delrin pretty inexpensively), Bing is not a low-budget project... probably three times the cost of a Robonova kit by the time it's all done. Also, not many people have CNC milling machines so probably a lot of the specifics of what I'm doing are not that "useful" for other builders on this forum. But hopefully it can be entertaining at least and maybe will inspire a thought or two in somebody at some point.

[DerekZahn]

While I work on little bits and doodads for Bing's feet, I thought it might be interesting to illustrate what I do to the servos -- I like to get position feedback which involves adding one wire to the servos. The processor inside the HSR-5995TG uses the voltage from the center terminal of the built-in potentiometer to determine the servo's position, so I want to expose that same voltage to my electronics.

I start by securely mounting the servo:



bigger: http://happyrobots.com/servo1.jpg

Removing the back of the servo reveals the electronics board, which has to be removed to get at the potentiometer. The motor is directly mounted to the electronics board in three places (two power leads and a case ground).




bigger: http://happyrobots.com/servo2.jpg

The solder has to be removed to get the board off. Do NOT try to just pry the board out. Either the motor leads will break or the back of the motor will come off, both bad! You could probably do this with solder braid but they make tools to do this sort of thing that aren't too expensive:



bigger: http://happyrobots.com/servo2a.jpg

Here's what it looks like with the solder removed:



bigger: http://happyrobots.com/servo3.jpg

Now the board comes off, revealing the insides of the servo. There are two spots that the new wire could be added -- either directly to the potentiometer or to the spot where the yellow wire attaches to the circuit board. I find it easier to attach it to the potentiometer.

There's a pretty sizable empty space above the potentiometer which leaves plenty of room for the new wire. If I recycle these servos someday for Bing 4, I might try putting the extra servo electronics into a little board that will mount directly onto the potentiometer, to provide a serial bus, position feedback, and maybe also current sensing. So it would be like the OpenServo project except I'd leave the motor control transistors and processing alone.



bigger: http://happyrobots.com/servo4.jpg

A lot of what I do is pretty delicate soldering, and it helps to have a decent soldering iron (though 50 watts is more than plenty). I also use the pointiest tips that I can find, and I keep them filed to a pretty sharp point. You're probably not supposed to take a file to the tips for some reason, but it works for me.



bigger: http://happyrobots.com/servo5.jpg

In almost all cases, it's a good idea to put a bit of solder on the end of a wire before attaching it to its destination. It makes the soldering go much more smoothly and makes sure that the wire strands don't go flying in all directions.



bigger: http://happyrobots.com/servo6.jpg

Here's the result after the modification. Besides adding the new wire, I also trim off part of the strain relief, because my designs tend to not like the big strain relief thing sticking out of the side of the servo.

I believe the servo warranty is no longer valid, ha ha!



bigger: http://happyrobots.com/servo7.jpg

Put the electronics back on and solder it back up. THe brown discoloration is just solder flux and is harmless.



bigger: http://happyrobots.com/servo8.jpg

And then put the back on again. I don't use the rear swivel so I use the alternate back.



bigger: http://happyrobots.com/servo9.jpg

[Joe]

If I recycle these servos someday for Bing 4, I might try putting the extra servo electronics into a little board that will mount directly onto the potentiometer, to provide a serial bus, position feedback, and maybe also current sensing. So it would be like the OpenServo project except I'd leave the motor control transistors and processing alone.

Neat work, Derek! You're braver than I — I'd be afraid to go modding such expensive servos (and with good reason, as I'd probably flub it up).

But now I have to ask... wouldn't it be both easier and cheaper to just use Robotis AX-12 servos? These already have a serial bus, position feedback, current sensing, and more, plus they're 16 Kg cm (stronger than these Hitec servos, I think?) and only $45 (substantially cheaper). Plus you don't have to void your warranty. Since you're everything else from scratch anyway, I'd think you could design your parts to fit whatever servos you want. So — if you don't mind me asking — why'd you choose the Hitecs?

Thanks,
— Joe

[DerekZahn]

At 7.4v, these servos have 30 kg-cm of torque (39 kg-cm of holding torque) and a speed of 0.12 seconds for 60 degrees. I have not seen any other servo that can match those specs in the two ounce weight range. I started collecting them about 18 months ago so there might be something new out but I don't think so.

So these have over double the standing torque of the AX-12, are about 50 % faster, and weigh about the same. The price, serial bus, and 300 degree range of the AX-12 are nice though!

[DerekZahn]

The DX-117 in the same product line looks like an outstanding alternative, with torque specs that are very similar to the hitec ones. That model wasn't available when I started designing Bing 3 and began collecting servos, and they are kind of pricey ($190 I think).

[Joe]

At 7.4v, these servos have 30 kg-cm of torque (39 kg-cm of holding torque) and a speed of 0.12 seconds for 60 degrees.

Zow, never mind then! I hadn't realized these were so beefy. You're absolutely right, you'd have to go to the DX-117 to get something comparable from Robotis, and those aren't nearly as compelling a value.

30 kg cm! Bing 3 should be quite a monster. Can't wait to see it when it's done. (Please be sure to put some good grippers on him — I hope to see him actually lift his opponent up over his head, and toss it out of the ring!)

Best,
— Joe

[DerekZahn]

Efforts to make various parts have resulted in a milestone being reached!

I don't intend to use the "bent aluminum bracket" building method very often, but it seemed like the best technique for attaching the ankles to the feet. When last you saw the feet, they had no covers attached but now they do:



bigger: http://happyrobots.com/bing3w.jpg

To help meet my goal of mimimum exposed wiring, I had to make covers for the ankle pods, which turned out to be a somewhat intricate task, but they came out fine:



bigger: http://happyrobots.com/bing3x.jpg

And finally, the finished assembly! Next step: knees!



bigger: http://happyrobots.com/bing3y.jpg

[bauermech]

You're doing some amazing work my friend. I too can't wait to see Bling3 in action. RoboGames '07? The 5995's are tough cookies. I used one in the waist on my bot, and when he was powered up it was a near impossibility to twist it manually. ...And they're quite fast

I love the added feedback mod you've made to them, and the delrin enclosures are brilliant!

[Joe]

Feet and ankles are assembled... seems to me that it's video time! Let's see those ankles twist and flex!

Cheers,
— Joe

[DerekZahn]

Thanks for the kind words Matt. I am definitely going to RoboGames and I hope Bing will be doing something by then! The construction isn't a problem, but the software is another story! I look forward to meeting other builders at RG!

Ha ha Joe, I don't think it's quite ready for video yet, but hopefully it won't be too long!

[DerekZahn]

My week of vacation between Christmas and New Year's continues, as yet another monster snowstorm attacks Colorado.

Instead of moving on to Bing's knees right away, I decided to make part of the torso because it seemed like fun to makea more complicated part.



bigger: http://happyrobots.com/bing3z.jpg

This is the part where the legs attach to the torso. On the bottom surface, I want to try to minimize the wobbling of the legs so I'm using some thrust bearings on the joint where the legs attach



bigger: http://happyrobots.com/bing3a2.jpg

Here's a shot with the bearings installed:



bigger: http://happyrobots.com/bing3b2.jpg

Here most of the components are placed in position for a test-fit.



bigger: http://happyrobots.com/bing3c2.jpg

[DerekZahn]

Lots of parts to make, and it's quite time consuming, but progress is being made. Here I'm cutting out some of the bits:



bigger: http://happyrobots.com/bing3d2.jpg

And here's a batch of parts ready for assembly. The black plastic parts are covers to hide the wiring as it makes its way down the legs.



bigger: http://happyrobots.com/bing3e2.jpg

I was hoping to have the legs finished in 2006 but I'm not sure I'll make it.