60-40 vs 63-37 Solder.

Today I learned a cool thing about soldering.

Solder is usually 60% Tin, 40% Lead, and this is referred to as 60-40.

When the solder joint cools, the different metals will solidify at different times, and there is a short time when one metal is solid while the other is liquid, called the "plastic phase". Unless the solder joint is kept absolutely still you risk creating artifacts in the joint such as voids and cracks that will decrease the quality of the joint considerably.

The solution is to switch up the numbers. You can find solder with the perfect balance of 63% Tin to 37% Lead which completely removes this problem.

So now you know what solder to get next time!

Wheeled rig update

Just a quick update on the wheeled rig. Electronics are starting to come together.

Power bar created.

• Main power bar was created and connected to battery.
• Relay board high end connected to power bar.
• Ribbon cable to carry signal between controller and relay boards was prepared with apropriate connectors.
• RC Servo pins soldered to stand alone PCB that allows for combining power with signal from different sources.
• RC Servo, ESC and power connected to RC servo board.
• ESC connected to power bar.
• Audio amplifier connected to power bar.
• Buzzer and warning light was connected to the power bar and relay board.
• Most circuits tested.

 Now only software remains!

Test circuit for RC servos.

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Wheeled rig update

So I put in some time on the wheeled rig:

OctoMY™ Wheeled rig with speakers, buzzer, warning light and electronics mounted.

Side closeup showing the battery mounting bracket and port holes where wires will be fed into the electronics box.

Front closeup showing the stereo speakers and alarm buzzer.

New features include:

• Created and mounted two separate stainless steel speaker housings made from the caps of  awesome waterwell™ bottles.
• Mounted a piezo deterrent/attention grabbing buzzer.
• Created a mounting bracket from stainless steel wire to hold the lead acid battery.
• Found the perfectly sized and shaped weather proof electrical box for mounting all the electronics for the robot.
• Created a mounting plate for the electrical box from an old plastic plate I had laying around my shop.
• Mounted a LED warning/attention grabbing flash-light on top of the electrical box.

Still on the TODO list:

• Mount all the electronics in a smart way inside the electronics box
• Connect all the electronics together and test it
• Protect the wires from wear/damage/water
• Protect the whole rig from water
• Paint job? Not sure about this

4-Wheeled rig build

I currently have 3 "rigs" I want to integrate OctoMY™ with. The hexy hexapod robot from arcbotics has been featured a few times before on this blog, but the other two have yet to be exposed. This post is about a 4-wheeled rig based on an old Traxxas TMaxx nitro engine RC truck.

This is how the tuck looked initially (with cover off).

At this stage I have stripped everytihng except the steering servo (which will be used).

Just a random "shop" image. This room is now painted gray and tidied up to look like a TV studio.

This is how it looks now with 12V Lead acid battery, RC ECU and mobile holder.

Closeup of RC-ECU and separate power for it.

Underside shows the geared electric motor (notice it is now only 2wd).

Closeup of mobile holder in front.

Right now it works as an RC car, but I will soon integrate it with OctoMY™. The current blockage is that the final step in discovery needs to be implemented (handoff, storage and use of recent connection parameters from discovery through to pairing). This part in turn needs some more UI work to allow sensible multiplexing between devices in remote.

Water cooled servo

I came over this really innovative solution to a common problem in robotics, namely the lack of power.

The hopelessly American solution as employed by robotics specialist Boston Dynamics as can seen in footage of their legendary big dog robot among others is simply to put a big noisy petroleum engine into the robot capable of driving the hydraulics system with the power they need to make it jump around like a gazelle on steroids.

Now another approach has surfaced that has more intelligence and lateral thinking to it. SCHAFT is a relatively small Japanese robotics company recently purchased by Google. They compete in the DARPA robot challenge, and have won at least one competition.

According to them the reason for their win is simply that they have managed to create "much stronger muscles" in their robots (higher power to weight ratio in servo motors). Their idea boils down to a brilliantly simple concept: Pump too much current into the motors but keep the motor from burning up by applying enough cooling.



So how do they provide more power? They solved this simply by raising the voltage of the power source beyond what a normal motor would endure and putting a capacitor bank between the power source_(battery) and the motors capable of delivering enough current even for the "spikes".

And how is cooling solved? They have constructed sealed motors that allows them to circulate non-conductive liquid coolant through the motors. The heated liquid pass through a passive heat exchanger that effectively dissipates the excess heat to the air around the robot.

I will definite look at ways of using this concept once I get the chance!

Choice of interconnect

I have been looking at different ways of connecting the different tiers of the robot that facilitates the following characteristics:

• Real-time
• Fault tolerant
• Embedded
• Low-power
• Broadcast friendly
• Master-less (survives
• Adaptive (survives topology changes)
• Bus architecture (many nodes)
• "Fast"

So far the most likely candidate seems to be CANbus.



I will investigate further.

Hybrid BLDC ESC & GX25 ECU

I have advanced my thinking about the power train. More specifically the details for the board that will handle generator stage has converged somewhat. This is the current idea:

• Use Brushless DC (BLDC) motor as both starter and generator connected to Honda GX25 motor.
• Build a simple DIY ESC circuit that when powered will rotate the BLDC shaft to start the GX25 (working as a starter motor).
• Build a rectifier circuit that when engaged to BLDC will make it generate power for charging batteries and giving the robot an extra power boost in the hour of need.
• Build an ECU circuit with inputs for tachometer, voltmeter, ammeter and outputs for throttle servo and mechanical relays that allows engaging/disengaging the ignition, ESC and rectifier circuits on demand.

GX25 BLDC generator

The basic API for the circuit should look something like this:

• Low-level
• Start engine
• Stop engine
• Set throttle
• Set charging
• High-level
• Start generator only when battery is low and/or power drain is high
• Adjust throttle to accommodate load
• Detect, alert and manage overheating
• Detect, alert and manage low-fuel
• Manage motor warm-up under different ambient temperatures.

How this circuit will communicate with central command and what will happen when communication breaks down is still to be decided.

Solar energy for cheaps

The robot will need all the power it can get, and solar panels has been a part of the plan from the start.

However, two problems with solar power has been evident that I have not been able to figure out:

• They are prohibitively expensive!
• They are fragile

Actually the last point may be a solution to both problems in a wired way, because I just discovered that solar cell manufacturers actually sell left over broken cells cheaply by weight or watt. Since they are already broken they will be less likely to break (smaller pieces) and fitting them into a lattice or grid will provide a flexible layout with the redundancy necessary to sustain power after loosing a single cell.


The plan is thus to buy some broken panels, cut them roughly to size and stitch them together in a grid with redundant connections.

Unboxing (unbagging)? of IOIO OTG

This is my second IOIO OTG. The first one was DOA.

UPDATE: DO NOT ORDER THESE, they were all DOA. Recommended supplier of IOIO is sparkfunn and seeedstudio.

STAY AWAY FROM GEEETECH IOIO OTG

This time I ordered x2 to make sure I didn't get a bad one again (returns takes ridiculously long time sometimes).


It is designed by this guy, manufactured by geeetech and was delivered by dx.com.

It promises to give you access to hardware comfortably from your Java IDE, Normally an idea I don't like but in the name of efficiency I decided to go this route instead of working my way through all the low level C/C++/AVR stuff to get some motors and servos moving.

The idea is to use it for prototyping and when it gets serious I will port my efforts to more robust platforms.

IOIO OTG with bluetooth adpater in the bag

IOIO OTG with bluetooth adapter unbagged

EMCO F1P Step motor specs

After my last post I have learned alot about step motors. I have also manged to figure out the specs of the step motors found in the EMCO F1P, and as always the quality of this machine turns out to be stellar.

My sources are:

Article on oriental motor. Explains the inner workings of stepper motors beautifully.

Article on stepper motors courtesy Douglas Jones of the University of Iowa.


The step motors in the EMCO F1P have 10 wires coming out of them. The wires are connected in consecutive pairs, one pair per two oppositely facing windings inside the motor (10 windings). The motor has almost no resistance when turning the shaft in un-powered state. The stator inside the motor has 50 teeth.

From this, I have gathered that this is a bi-polar, uni-filar, 5-phase motor design with 50 * 10 = 500 steps and 360 / 500 = 0.72° rotation per step.

This kind of motor is less common, and requires a more complex/expensive driving circuit. It offers higher precision, less vibration and noise and more torque at mid to high speeds than the more traditional 2-phase designs. Also there are more ways in which the driving circuit can drive it.

This has made me determined to keep the motors and find a new controller for them during my retrofit-project.

Anatomy of a step motor

I decided in the beginning of 2015 to stop spending time on my EMCO F1P CNC machines instead of the main goal of the proejct. Ironically that made me spend more time on the CNC,because I need to get them out of the way quickly.

Long story short, I want to convert one to use a new control board but without sacrificing the step motors. So I have now carefully removed one step motor (Z-axiz) and opened it up to see what's inside it.

Based on what I have gathered from searching around and posting a question on stack exchangel, this motor is most likely a bipolar motor with 10 windings.

Some pictures:

10 coils

Coil wiring

5 Screws

Removed connector housing.

10 wires + ground.

Motor removed from belt

Belt drive with tacho generator

Heat-sink with thermal paste.

Power and electronics schematic

I made a first sketch for the power and electronics diagram for DEVOL.

DEVOL power and electronics schematic

In essence the robot will rely on a 12V lead battery as the main source of power. A small gasoline powered generator will serve as a means to keeping this battery charged when in the field.

Power will be distributed from the battery via two separate regulators, a delicate and stable regulator for controllers and logic and a more robust and protecting  regulator for the power-hungry actuator motors.

The system is kept modular so that the different components such as visual input, strategic planning and real-time control may be handled by a separate computer (I suspect that especially the vision part will require a rather powerful computer).

The actuators are connected to a serial bus that distributes commands for each actuator from the real-time controller. Power is distributed along a separate power rail.

Visual input is provided by a calibrated stereo pair (two Logitech 9000 Pro) and another "long range" camera (Logitech 9000 Pro with mounted tele-lens). The whole camera rig is supposed to be put on a pan-tilt rig, guarded from the elements by a glass/plastic dome.

For audio, a hand-held zoom H1 stereo recorder, which provides high quality, low latency sound card and high quality microphones requiring very little power. It also has a third input where I intend to plug in a "long range" so called "shotgun microphone".

This is the first draft, expect drastic changes!

Unboxing electronic components batch #1

My first electronic components arrived today, and I am thrilled! This is however probably not the last time I will be unboxing electronic components on this blog. In fact, I allready need to order replacements after I accidentally ordered all my diodes in SMT instead of through hole form factor, which I needwhen working with a breadboard. On to the unboxing:

Unopened box

Lots of antistatic wrapping and padding

All content before unbagging

511-TIP102 Transistors

844-IRFZ48RPBF Transistors

863-MBRS140T3G Schottky diodes (FAIL: i got SMT instead of though hole).

863-MMBZ5240BLT1G Zener diodes (FAIL: i got SMT instead of though hole).

604-WP154A-RGB RGB Full color LEDs

625-1N4933-E3 Diodes

10w 4.7 ohm resistors for simulating loads

551-PS2501-4-A 4 channel optocouplers

511-TIP107 Transistors

652-4308R-102-ZLF-1K 4 channel 1 KOhm resistor arrays

652-4308R-102-ZLF-10K 4 channel 10 KOhm resistor arrays

652-4308R-102-ZLF-560K 4 channel 560 KOhm resistor arrays

All sorted in boxes, with the mouser Serial number labels intact for reference (not all the components have specs written on them).

Unboxing gloves and UV developing fluid

Just a short post today. I have received the UV photo resist developing chemicals and protective gloves that i forgot to order when I ordered all the other PCB etching stuff.

Just a simple bubblewrapped envelope this time.

UV photo resist developing chemicals. To be mixed with water.

Protective gloves for working with etching chemicals without burning your fingers off.

I need a H-Bridge part #4

Today I finally got my act together and ordered some electrical components for the H-Bridge. This is the first time I ever order electrical components, and i must say that mouser.com is really great. My day job is making websites, and although it looks a bit boring and old fashioned, they sure make up for that with some really great usability! Also, I like that they are close to 1/2 the price of my local dealer even after tax and shipping. Here is my rather juicy shopping list:

Mouser No: 863-MMBZ5240BLT1G
Mfr. #: MMBZ5240BLT1G
Desc.: Zener Diodes 10V 225mW
25 $0.09 $2.25 25 Pending Pending -

Mouser No: 863-MBRS140T3G
Mfr. #: MBRS140T3G
Desc.: Schottky (Diodes & Rectifiers) 1A 40V
25 $0.288 $7.20 25 Pending Pending -

Mouser No: 844-IRFZ48RPBF
Mfr. #: IRFZ48RPBF
Desc.: MOSFET Power N-Chan 60V 50 Amp
16 $3.02 $48.32 16 Pending Pending -

Mouser No: 604-WP154A4-RGB
Mfr. #: WP154A4SUREPBGVGAW
Desc.: Standard LED - Through Hole RGB Full Color
16 $1.86 $29.76 16 Pending Pending -

Mouser No: 588-30J4R7E
Mfr. #: 30J4R7E
Desc.: Wirewound Resistors - Through Hole 10watt 4.7ohm 5%
16 $1.81 $28.96 16 Pending Pending -

Mouser No: 625-1N4933-E3
Mfr. #: 1N4933-E3/54
Desc.: Diodes (General Purpose, Power, Switching) 1.0 Amp 50 Volt
16 $0.05 $0.80 16 Pending Pending -

Mouser No: 551-PS2501-4-A
Mfr. #: PS2501-4-A
Desc.: Transistor Output Optocouplers Hi-Iso Photo 4-Ch
10 $1.61 $16.10 10 Pending Pending -

Mouser No: 652-4308R-2LF-1K
Mfr. #: 4308R-102-102LF
Desc.: Resistor Networks & Arrays 1K 8Pin Isolated
25 $0.374 $9.35 25 Pending Pending -

Mouser No: 652-4308R-2LF-560K
Mfr. #: 4308R-102-564LF
Desc.: Resistor Networks & Arrays 560K 8Pin Isolated
25 $0.374 $9.35 25 Pending Pending -

Mouser No: 652-4308R-2LF-10K
Mfr. #: 4308R-102-103LF
Desc.: Resistor Networks & Arrays 10K 8Pin Isolated
25 $0.374 $9.35 25 Pending Pending -

Mouser No: 511-TIP107
Mfr. #: TIP107
Desc.: Darlington Transistors PNP Power Darlington
16 $0.619 $9.90 16 Pending Pending -

Mouser No: 511-TIP102
Mfr. #: TIP102
Desc.: Darlington Transistors NPN Power Darlington

Electronics terms part #1 - Transistors

Since I am all new to electronics, I thought I would summarize the terminology I pick up in this blog along the way.

Since I am designing and building a H-Bridge now, transistors and diodes have become very important components. I will therefore start with a little post about terminology related to transistors.


Transistors are switches with 3 pins that let current pass from the "collector" pin to the "emitter" pin only when there is sufficient current applied to the "base" pin.  We often talk about "open" and "closed" states, when talking about transistors either conducting or not conducting respectively. The following are important characteristics for transistors:

• Type. There are several different ways that transistors are made, each with its own set of pros and cons. Each type has a name that often gets identified with the characteristics typical for that transistor type. This is the complete list, and here is a summary for the most common ones:
• MOSFET (metal oxide semiconductor field-effect transistor). This is the predominant type of transistors today.
• Darlington. When two transistors are connected in such a way that the current amplified by the first transistor is amplified further by the second one create a single transistor with a significantly higher current gain. A "darligton transistor" refers to a single IC that incorporates a pair of transistors in this configuration.
• BJT (Bipolar Junction Transistor). This used to be the predominant type of transistors.
• Power MOSFET. This is a MOSFET designed to handle significant power levels. Its main advantage over IGBT is higher commutation speed.
• IGBT (Insulated-gate bipolar transistor). Made to tolerate significant power levels. Pros include high efficiency and fast switching.
• Package. How does the transistor look like, how big is it, and what power dissipation characteristics does it have? (more on dissipation below). Common packages include: TO-92, TO-220 and TO-3.
• Voltage drop. Transistors are not perfect conductors, and there are two voltage drops, one between the base and emitter pins (when in the open state), and one between the collector and emitter pins. These two voltage drops are called Vce(sat) and Vbe respectively in the transistor data sheets. Typical values for these voltage drops are 0.1-0.2V and 0.7V respectively.
• Commutation speed. This is how long the transistor spends going from a "open" to a "closed" state and vice versa. Usually specified in the time per commutation (milliseconds/nanoseconds) or in number of commutations per second (Hz).
• Forward breakdown voltage. The voltage required before the transistors "give in" and let current flow even though it is not in the open state.
• Max operating temperature. How hot the transistor can become before it stops working temporarily or permanently. 
• Power dissipation. How much power the transistor package is able to safely transform into heat during operation. Bridging the transistor to a surface that efficiently conducts away heat such as a heat sink can increase this power dissipation which in turn will allow for more current to pass through the transistor before it will overheat.
• Drive current. The amount of current that the transistor can pass in the open state.
• Current gain. The ratio between how much current is required to trigger the transistor and how much current can pass in the open state. Current gain is referred to as Hfe in transistor data sheets.

Since I am just learning this stuff myself, please feel free to correct me! And don't rely on this information without verifying it with another trusted source first!

I need a H-Bridge part #3

My two last posts about this subject were rather general. I have since then ordered some equipment, and spent a lot of time thinking about how to build my motor control board. This post will summarize what I have pondered thus far.

• I will first build a working circuit of the power part (H-Bridge) of the motor control board  using a breadboard. I will play around with it, and switch components and wiring until i can get it to work optimally. I will use my RB-100 controller to drive it.
• Once I am satisfied with the power part, I will continue with the control part. In this stage I will use the RB-100 to send commands to the control part over I2C or similar, and create software on the receiving end using a PIC controller on board the control board that in turn will drive the power board.
• Once the whole configuration has been thoroughly tested and works flawlessly under all sorts of extreme conditions such as motor stalls/ over-power/under-power/ forced reversal, extreme temperatures, and once I get optimal power efficiency, I will continue by making a compact set of PCB layouts, and continue with etching them and building the first version.

For the power part, I have gathered a set of information resources that I think is really good. Here is a list of links:

• General tricks for PCB layout.
• A comprehensive lot of in-depth quality information about building a performance H-Bridge (H-Bridge secrets). Part2 and part3.
• Beginner introduction to H-Bridge construction.
• A collection of implemented H-Bridge designs with notes.
• Step by step implementation of a H-Bridge design with component specs and prices. 

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Unboxing breadboard and bench top power supply

I just received a bench top power supply with adjustable voltage (0.0 - 32.0 VDC) and current limit (0 - 2 Ampere @ 32V), together with a breadboard kit and an anti static mat for my workbench. I will use this to build the controller cards for the motors in my limb prototype.

Box, unopened.

Pink inflated wadding.

My stuff!

Anti-ESD conducting rubber bench mat

Bread board.

Jump wire kit for bread board, bubblewrapped.

The power supply, boxed.

Opening the power supply box.

Out of the bag.

Front panel.

Back side heatsink.

Bread board unboxed.

Jump wire case closed.

Jump wire case open.