Progress Report (not really a progress)

[barbar]

got no movie cam, sorry

[Pev]

awesome - finally a robot with a proper use lol. Nice idea to change the hands for more grip

Pev

[barbar]

Huge problem: Beer Butler Bot needs at least rotating wrists (a further distance sensor would also do well). I can't find any other method to make him "find" and pick up the bottle from the table before he fills the glas. Because he his so tall, I always have to hold up the bottle to make him grab for it - and that simply can't be the final result since he has a whole lot of work to do before he pays off.

Who can help with two AX-12? Limor?

[roboLucy]

Wow! that's cool~ good sense barbar!!
it's amazing to have such as shining idea with Humanoid.
Humanoid which is made by AX-12 limit to 18 joints.
If more than 18,you may have some trouble because of torque shortage of actuator.

I'm really expecting your next work ..

Lucy.

[barbar]

shining idea

Thanks. Laziness makes inventive .

If more than 18,you may have some trouble because of torque shortage

Would you be so kind as to explain the decreasing torque effect a little bit more in detail. Are there any empirical values? (such as: 18 AX-12 = 100% torque, 19 AX-12 = 90%, 20 AX-12 = 80% ...)

Or exemplarily: If I was to connect 25 AX-12, how much would the torque reduce? And is there any possibility of compensating that effect? Increasing the voltage?.

Your answer would be important because I am planning to increase my AX-12 and AX-S1 collection.

Thanks in advance.

Cheers!
barbar

[stevo3d]

Barbar,

My guess is that she meant the weight of additional AX-12s would become an issue. For example, if you were to add more AX-12s to the upper body of the humanoid, the added weight would make it more difficult for the leg and waist servos to move and maintain position.

[coldguy]

And is there any possibility of compensating that effect? Increasing the voltage?.

Not voltage, current. Too many servos, moving under load at the same time, I suspect would require more current than a single battery could provide. Batteries have an internal resistance which is negligable at lower current draws. As the current draw increases (as with more loaded servos), the internal resistance of the battery becomes significant enough to cause a voltage drop across it, reducing the output voltage. This limits the amount of current a battery can deliver. (I learned this from trying to run an automotive starter motor from 9 AA batteries in series.) Its the same reason your lights dim when the fridge kicks in. The high current to start the compressor in the fridge causes a voltage drop across your breakers/wiring.

The solution is to get a bigger battery, or spread the load across more batteries by wiring them in parallel.

The 3 conductor cables that connect the dynamixel servos are similar enough to how a standard servo is connected. The 3 wires are Vdd(+power), Gnd(-common) and data(TTL for dynamixel AX-12, pulse width modulation for standard servos). The Vdd and Gnd on a standard servo are connected directly (or through a fuse) to the battery. If you look on Robotis' web site for information on the Cycloid robots, they have multiple battery packs in the knees and shins. The packs plug into the closest open Dynamixel serial port, and are therefore wired in parrallel, to boost available current.

You must also consider the mechanical load on the servo. RoboLucy may mean that the plastic gears may fail with too much weight, or the servos may just not be able to lift the extra weight, regardless of the availaple power. Remember, an electric motor has its most torque and its highest current draw at stall. When its trying to move something and just can't do it, that's when its consuming the most power and converting it into heat energy instead of mechanical energy. That's when things go up in smoke!
You may want to monitor the internal heat of the dynamixels if you build any HUGE robots.

[barbar]

Current of course, Thanks (now you know why I had to quit studying electrical engineering )

[limor]

barbar's pictures hit slashdot

[Gil]

How much force do those motors have and how much does that bottle weigh?

[abbtech]

Nice job This is what I call a valuable robot! Got a video of the pour?

[barbar]

@limor: You could have given me the chance to wipe the table before all of them see the mess ... 8O

@Gil: It was a full 0,5 litre beer bottle. But it also worked with a full 1 litre water bottle (robot has to lean more to the back though, when holding it in front of his chest). edited later: plastic bottles.

These are the techspecs of the servos called AX-12:

Weight (g) 55
Gear Reduction Ratio 1/254
Input Voltage (V) at 7V at 10V
Final Max Holding Torque(kgf.cm) 12 (at 7V) 16.5 (at 10V)
Sec/60degree 0.269 (at 7V) 0.196 (at 10V)
Resolution 0.35°
Operating Angle 300°, Endless Turn
Voltage 7V~10V (Recommended voltage: 9.6V)
Max. Current 900mA
Operate Temperature -5 ~ +85??
Command Signal Digital Packet
Protocol Type Half duplex Asynchronous Serial Communication (8bit,1stop,No Pa
Link (Physical) TTL Level Multi Drop (daisy chain type Connector)
ID 254 ID (0~253)
Communication Speed 7343bps ~ 1 Mbps
Feedback Position, Temperature, Load, Input Voltage, etc.
Material Engineering Plastic

@abbtech: no, sorry! (but I've got the video cam on my shopping list)

Cheers!
barbar

[Gil]

Guys...Check this out

[barbar]

Guys...Check this out

[roboLucy]

Would you be so kind as to explain the decreasing torque effect a little bit more in detail. Are there any empirical values? (such as: 18 AX-12 = 100% torque, 19 AX-12 = 90%, 20 AX-12 = 80% ...)

Or exemplarily: If I was to connect 25 AX-12, how much would the torque reduce? And is there any possibility of compensating that effect? Increasing the voltage?.

Hi BarBar,

To decide Torque that need to robot is possible by Simulation or simple calculation. However,you only can have exact result with real manufacturing
because there is various exception element. Our conclusion is that can be rich like attached video clips when we manufactured with 18 joints in present structure.
This assembly drawing and example program are going to be launched soon.

Joint that Torque is lacking is Roll in upper part of leg and knee. If upper body is heavier, can solve the problem by making leg short. 4 DOFs _ biped is the case of made step using minimum joint. please refer to attached video clip.

we are not recommand to increase voltage because it is very dangerous method.

Also, one more method is using Dynamixel, which is more high efficiency instead of AX-12.
More detailed specification of Dynamixel can search around in July after homepage reorganization .

Sorry for late reply actually i needed some time to discuss about this issue with our engineer people.
hope my writing will be little help for you. see the vidio clip please.

thanks.

Lucy.

http://211.238.207.44/~robotis/upgrade/HumanoidWalk(Ordinary).wmv

http://211.238.207.44/~robotis/upgrade/4DOF_biped.wmv