Powering poppy with OpenServo V4

Technology
1

This topic is about using the (currently) under development OpenServo V4 to power poppy.

The intention is to offer a much lower cost servo, so that not only does the cost reduce of making poppy, it simplifies poppy by only using a single type of servo.

This servo is USB controlled and uses 2.43mA (vs 100mA for MX-28 / 64) when not moving and has the possibility to drop down to 100nA when in standby to preserve the battery.

A later version may well use USB 3.1 which allows 12v at 5A down the USB cable so only one cable would then be required. But we have to wait for the standards board co confirm the new specification in July.

It is likely to be exactly 153% of the size of a MX-28 servo and initial indications are it will be between 40 & 50 Kg/cm of torque. (i.e. print poppy at 153% scale and just add these new servos, so poppy would now be 128.5 cm tall).

This means that if you print out a version of poppy with only MX28 servos at 153%, you are all ready to go (though the internals of the head will also expand); BUT, ideally the horn size would remain the same, but we may simply scale that up to, it depends on how difficult it is to scale poppy.

Further, this servo has a JTAG debug port and open source RTOS on it so people can expand it and add their own routines, as well as it has a 3D accelerometer, current sensor, temperature sensor, can detect if the motor power is lost and in ASCII mode can be controlled simply via any program (even a terminal emulator) and looks like a standard serial port over USB (i.e. a CDC device) and has been tested on OSX, Linux and Windows.

We are looking at a binary mode where a user can use LIBUSB and Python (as an example) to control the servos and react to various thresholds, for example if the servos detect a freefall or sudden knock, it can interrupt the host and interact in whatever manner is required.

We have built the initial prototypes, and are looking at build the new scaled up prototype that I have mentioned above.

Here is a link http://www.openservo.com/forums/viewtopic.php?t=925&postdays=0&postorder=asc&start=180&sid=61c923ed2426c4dfa844de43901b65035 this shows a prototype before we move to the new case design.

The price is going to be much cheaper than a MX-64 or 28 and runs at 11.1v (i.e. 3S LiPO battery)

I do not have the skills to modify poppy to meet these needs, and may well need to assistance in this area.

Cheers Douglas

1 Like
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Do you talk about only the protocol of USB2.0 or use the USB3.1 protocol which use more pin on connector to increase communication speed?

The problem is currently a lot of people don’t have USB3.0 on computer. And it will be an obstacle for the motor.

Currently we use 14 V to have the best torque in comparison to current used.
But the design choose for the power supply board is standard and you can, with a little compute, modify the value to have on out 11.1V

Yet, I think it would be difficult to use directly a 3S LiPO battery because the lack of regulation and the motor’s number will create a big inrush current and the voltage will fall down and reset the motor logic.
But with 4S and regulation, it will work good I think.

3

Really interesting project.

You could but you would not need to scale the whole robot at 153%. We just need to have the case dimensions and modify the horn fixation design.

Do you have mechanical drawing ?

4

Hi Team,

We are currently designing the case and will probably have an initial prototype ready in about a week.

If poppy does not need to grow, I am fine with that. If someone wants a taller poppy (pardon the pun), is that relatively easy to do using the parameter approach of SolidWorks?

Cheers
Douglas

5

We will offer initially a USB2.0 interface, we are unlikely to offer a USB 3.1 interface until the new connector is widely available which is at least 1 year away.

Interesting thoughts on voltage vs current vs torque. I would like to test this on a poppy to see how that goes, it may influence the choice of motor we use.

The main CPU is powered from the USB and so far I have had no problems with noise from the motor, even under heavy loading, only the motor driver chip is powered directly from the battery supply. Though I do note that I have not tested a servo on a LiPO battery (I am using a 0-20v, 40A power supply), nor yet used a voltage regulator to power all the electronics and motor from a common source.

6

If you’re in the case design phase, any chance of designing it to the same case dimensions as the Dynamixel servos? You’ll have a lot more interest in your product if that could be done (and not just from the Poppy community).

7

Our original intention was to duplicate the form factor, but to purchase motors of that size with the torque needed are very expensive, the larger motors are much much cheaper. So it is the tradeoff, 50% bigger and much cheaper with room for many more features, or a similar price and same size.

8

When can we get the finished product, I mean MX 64 clone. May be bigger in size but cheeper :smile:
Please keep the horn same as MX 64 that will help eliminating new frame designs.
What will be aprox price you have in mind ?

NicoX

9

Hi,
I need to get a final hi-res 3D print made of the prototype case done in the next 2/3 weeks and the I am looking to crowd fund (I will post a link here so if people are interested, then they can help get this product to market) the injection mould and first production rum.

The software is virtually finished.

I am looking at the feasibility of have the same servo horn layout as the MX64, but the spline needs to match the output shaft I am using so I need to look into that.

I am planning to have these in the market before the end of the year.

Cheers
Douglas.

2 Likes
10

Was this project ever completed? If so, can I please get more details on it? I’m wanting to build a poppy but the dynamixels are still quite high priced. Thanks!

11

I put the project in hold as while the product is designed and ready to go into production, I was not sure about the market size and probably could use a kickstarter to get to market. I do not have Solidworks to adjust the model.

12

Hello, Solidworks is needed for the part I’ve seen in the link above or for the servo?