Micro Hex Walker input requested

Hi everybody

I’m working on a micro hex walker. I’m aiming for a body size on 20mm by 60mm and under 50g.

Attached in low res PCB and i’ll add the schematic in the next post

Included on the board(20mm x 60mm):
A 1A lipo charger, set up for 500mA charging.
A self learning lipo fuel gauge and cell protector.
A switching regulator to convert 3V-5V to the required 3V3.
14 picoblade molex connectors connected to pins on a USBizi100. These can be servo headers or any other sensor inputs(for other projects).
A I2C light sensor and I2C header for sensor expansion.
A bluetooth module for debugging or control.

One thing that I’m not sure of at this time. If the chip is powered down, ie no 3V3, and there is a pullup to 4V on a pin, will current flow into this pin via ESD protection diodes? The spec says that the I2C pins will not pull the bus down if the chip isn’t powered, but I can’t see anything for the rest of the pins. This question is related to the DQ pin of the fuel gauge that is being pulled to the battery voltage. According to the fuel gauge chip, if you pull this pin low via a switch then it will power up the rest of the circuit via it’s protection FETs.

Anything else that I should look at?


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As you can see, I based it on the Fez Mini circuit… :slight_smile:

:o you are copying the minis schematics!!! You can’t do that…

of course I am kidding :slight_smile: This is a super mini

Hahaha Gus, he probably got a heart attack reading the first line ;D
Looking good! I am thinking of designing a board with a USBIZI too.

Looks neat! Is there any way to increase number of connectors? 18 servo motors minimum.

Hi Errol… looking great… I dont know if you want to include pin “19” (VBAT) on the USBizi; FEZPanda 2 uses it for some shields; like the FEZConnect for the “Super CAP”… pin 19 has a shottky diode there… keep up the good work.

@ Gus: You teaser! :slight_smile:

@ Robert: Thanks. It’s kinda liberating to design a board with just the features you need… :slight_smile:

@ Architect: I’m still waiting for the servos. They either have a 1.25mm pitch JST or 1.25mm Molex. Once I have them then I can see the exact connector. Once i get the mating connector then I can see if I can squize more connectors on there. I would also like to make the legs 3DOF later, maybe still with a 2DOF head, which will be 20 servos… At this point though there isn’t ANY space… :frowning:

@ Alex: The VBAT is used for the battery backed ram and RTC. I would like those features, but don’t have space for the crystal or the supercap/battery.

I did realise that there is an issue with the fuel gauge wiring. The pull up on DQ goes to the switched power side. Thus when the power is off then there is no pull up on DQ and no way to toggle it to turn the power back on. It must be pulled directly to the battery +… Will try to fix that this weekend.

Ok, added a level shifter between the fuel gauge and the USBizi.
Also added 4 more servo headers for a total of 18 servos, just couldn’t fit 2 more for 20… :frowning:

Note that the servo connectors are for sub micro servos, molex picoblade, 1.25mm(0.05") pin spacing.

Sent the board files to DorkbotPDX yesterday. Now I wait… :slight_smile:

I am interested in buying one out of 3.

Maybe wait for Rev2… :slight_smile:

Already found that, in my hurry to make the DorkBotPDX deadline, I neglected to connect one of the servo headers… So it’s only 17 servos in this revision… :slight_smile:

Also would like to test the PSU side before committing boards to anyone… :slight_smile:

Also note:
Servo connectors are ultra small.
Servos will be powered directly from one lipo cell, and must thus be 1S servos. See bottom.
The charger is for charging one lipo cell.
The fuel gauge is for one lipo cell.
There is a PSU on board to boost the lipo voltage to 3.3V but there is no 5V available.
There is a footprint for an obscure ebay bluetooth module.

Designed for servo(1.7g):
Might also work, don’t know about connector, will test in phase two(2.2g):

Designed for this battery:
But any single cell lipo will work.

Alright, will wait for v2. ;D

Any chance you’d share what crystal you’re planning to use, and what footprint it occupies? Eagle’s library of SMT crystals seems… bare… to me.

I’m using “CRYSTAL5X3 (CRYSTAL)” from the SparkFun library.

And i’m using this part:

Part 648-0165 from RS Components.

But I have not done 100% “part to footprint matching”.

Still waiting for my boards, but did some 3D rendering with EagleUp.

dimensions are in meters due to a thing with EagleUp. It is actually in mm… :slight_smile:

And the other side

Looks awesome. Never heard of eagleup!

Yeah, neither have I before Saturday. It’s plug-ins for Eagle and Google SketchUp to export from Eagle into SketchUp… :slight_smile:

Works quite nicely. I just don’t know enough of SketchUp to draw half decent parts… :slight_smile:

Very nice! I am going to check out EagleUp as well.

Ok, my servos still has not shipped from HobbyKing and it’s been a month… :(.

So I made a 3D mock-up… :slight_smile:

Excluding the wires to the servos the robot is 72mm long, 48mm wide and 35mm high…

Will probably still work on the knees…

That looks awesome. I think it would make a great educational kit for schools.