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Little Flash

Little Flash runs for twenty minutes, charges in ten seconds.

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Little Flash is a 3d printed robot powered by ultracapacitors. To prevent getting stuck, she uses a bump switch and random path adjustments.

Making a couple of changes to the design allows me to reduce the part cost by forty percent.  Here's Little Flash (left) and Little Flash 2 (right).

Daren Schwenke suggested a modification to the servo motors that allows me to remove the Arduino motor shield (a costly component). I do lose current detection, but that seems to be insignificant in the scheme of things. Changing the dc to dc converter to a "non metered basic unit" reduces costs further.

This year's competition is about moving toward a market solution for a given device--I thought I would at least try to move toward lower costs while maintaining functionality for Little Flash.

Little Flash is powered using three 350 farad capacitors (in series). Her drive motors are metal gear servos (with electronics and end stops removed). 

Currently, she runs for over 25 minutes on a single charge and the charge is supplied using a constant current supply (10 amps for 40 seconds). 

I expect to use three 3000 farad capacitors (in series) to quickly charge Little Flash--this could result in Big Flash; something we'll see in a few days.

ino - 2.41 kB - 05/31/2019 at 17:29

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Standard Tesselated Geometry - 526.74 kB - 05/15/2019 at 21:34

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Standard Tesselated Geometry - 342.66 kB - 05/15/2019 at 21:34

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Standard Tesselated Geometry - 133.87 kB - 05/15/2019 at 21:34

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  • Convert Servo Motor to Geared Drive Motor

    Mike Rigsby05/23/2019 at 17:17 4 comments

    For a metal gear drive motor, easy to attach to wheels via servo horn, I modified a "no stop" servo motor. 

    Start by removing the four screws in the bottom of the case.

    Next, cut the two wires from the circuit board that go to the motor.

    Cut the three wires from the circuit board to the potentiometer. Remove the circuit board.

    Take the two wires from the motor and solder extender leads.

    Push the solder connection joints into the cavity of the servo motor housing.

    Screw the bottom cover back into place.

  • Robot Construction

    Mike Rigsby05/22/2019 at 18:36 0 comments

    Take the 3d printed wheels and add vacuum cleaner belts for tires.

    Attach the Servo horn using 3mm screws.

    Solder the capacitors in series and place them in the 3d printed capacitor holder (along with the on/off switch). Solder the (female) charging cable.

    Attach the Arduino (with motor control shield) and dc-dc converter to the back of the blue capacitor holder. I used velcro for attachment.

    Attach the lever switch and bracket to the robot body.

    Add the "bump switch blade" to the lever switch bracket using 3mm screws. The blade should move very freely.

    Secure the motors to the robot body (3mm screws). Add the wheels to the motor shaft (using the servo horn screw). Attach the capacitor holder to the robot body using screws. Attach the caster ball holder to the robot body using screws.

    Insert the caster ball.

    Set the output voltage for the converter to about 8 volts. Program the Arduino, charge the capacitors and she's ready to run.

  • Fast Charge

    Mike Rigsby05/20/2019 at 19:52 2 comments

    Today is the big day--I prepared to (from a distance) connect 9000 charged farads (8.1 volts) to 1050 partially discharged farads (3.5 volts).

    Nothing spectacular to report--probably got enough charge (in ten seconds) to run for 20 minutes.

    Peak current during the transfer was around 45 amps and the hottest physical component (plug connector, #18 wire) reached 122 degrees F. The wiring and the connector represent about .1 ohm, so that resistance limits the transfer.

    To charge Little Flash in one second, I would need to transfer about 400 amps. The connector and wire size to accomplish that (for a one pound robot) seem impractical--so I'll be happy with a ten second charge for now.

  • Preparing for Fast Charge

    Mike Rigsby05/17/2019 at 20:40 5 comments

    Using available materials, I'm preparing for the first "pretty quick charge" test.

    Using painter's tape to secure the 3000 farad capacitors to scrap plywood, I wired in an automobile starter solenoid (rated for about 300 amps). 

    I plan to stand about 15 feet away (and operate the entire setup on concrete) when I connect "9000 charged farads to 1000 depleted farads." It should be interesting and will probably occur Monday, May 20.

  • Schematic

    Mike Rigsby05/16/2019 at 20:39 0 comments

    Little Flash just runs around and stays out of trouble, but it's somewhat relaxing to let everything else go and just watch the movement. As John Lennon observed, "Time spent doing nothing is rarely wasted."

    The schematic diagram for the robot is shown below:

    The Arduino sketch for operation is available in the files on this site.

View all 5 project logs

  • 1
    Little Flash 2 Construction

    We start with the pieces on the floor.

    Next, we examine the schematic.

    Solder the capacitors and on/off switch together. Place them in the capacitor holder.

    Add the dc to dc converter to the switch side of the capacitor holder.

    Solder leads to the lever switch.

    Place the lever switch in the bumper bracket using 3mm screws and nuts.

    Prepare the bumper to attach to the bracket--it will attach using 3mm screws that thread into the bracket.

    Gather the wheels, servo horns and vacuum belts. Attach the servo horn using 3mm screws.

    Place the "tire" (vacuum belt) on the wheel.

    Drill holes and attach the bumper assembly to the frame.

    Drill a hole and attach the caster bracket to the rear of the frame.

    Insert the caster ball into the bracket.

    Next, we modify the servo motors. Remove the screws from the backplate.

    Remove the small "silver" screw (below the circuit board) that holds the pot in place.

    Pull the pot straight out.

    Cut the three wires and remove the pot.

    Combine two 2k resistors. Solder the center wire to the connection of the two resistors.

    Solder one wire to the end of a resistor and the other wire to the free end of the other resistor.

    Tape the resistor assembly so that the resistor ends cannot make contact with anything else.

    Insert the circuit board and resistors into the motor cavity. Screw the back on.

    Using a file, remove the plastic nub on the servo mounting bracket.

    Install the motors in the frame using 3mm screws and nuts.

    Place the wheels on the servo shaft. Secure the wheels using the servo horn screw.

    Route the wires between the motors toward the back of the frame.

    Pull the wires through the hole in the capacitor holder and secure the capacitor holder using 3mm screws (holes will need to be drilled in the frame).

    Solder two 1 Mohm resistors together. Add a wire from the center connecting point and insulate the assembly.

    Solder one end of this assembly to "+ input" on the dc to dc converter. This device is used to monitor supply voltage and trigger the Arduino's onboard led when the supply voltage drops below about 4 volts.

    Install the sketch for the Arduino (found in the files), then plug in all the wires according to the schematic and tie wires up for appearance.

    Charge the capacitors, flip the switch and it will run just like Little Flash.

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Discussions

Daren Schwenke wrote 05/23/2019 at 16:39 point

1/4" soft (or rigid if you like) copper pipe makes pretty good 200A+ buss-bar at a fraction of the cost of real ones.  Squish the ends in a vise or with a hammer, drill through, and then you have termination points as well.  

Lighter weight could be had by using refrigeration tubing, although it's usually the same price, and for the transfer duration that would probably be fine.  On the other end of the spectrum, Type L water pipe can handle 800-1000A.

  Are you sure? yes | no

Giovanni Carrera wrote 05/23/2019 at 15:32 point

I used supercapacitors (0.1F @ 5V) about 30 years ago to maintein the data in the CMOS rams to replace the batteries and they worked fine. In your case I still find them very expensive for an energy value of only one Wh, I have to spend a lot and I have large dimensions and weights, especially when compared with Lipo batteries.

The Maxwell 350F supercaps have a very low internal resistance (2.2 mohm) and you should use short wires with a very large section for maximum energy transfer.

  Are you sure? yes | no

Davinder Chandhok wrote 05/23/2019 at 11:31 point

Did you consider using a delrin caster ball as opposed to a printed one? It seems like the printed one would cause unnecessary friction.

Also, are you running at 9 V on the bot? I'm wondering how long I could run a Raspberry off of the supercaps, as long as I have it bump into a charging station every so often.

  Are you sure? yes | no

Mike Rigsby wrote 05/23/2019 at 13:09 point

You are correct--the printed ball creates friction and (worse to me) is often noisy. Of course, the printed ball can be fabricated at any size or any color--so I appreciate the shallow value of "how it looks."

In this specific configuration, my dc-dc converter is set for an output of 7.7 volts.  The robot (Arduino, shield, motors, converter) draws roughly 250 mA. Starting at a charge of 8 volts and draining to 3.5 volts gives me 25 minutes of run time. So, my steady output energy equals 250 mA at 7.7 volts for 25 minutes. If I start at 8.1 volts and discharge to 2.8 volts (questionable bottom limit of dc converter), I would get a little more time. This dc converter includes a power hungry voltmeter (which is blue and looks cool--I'm somewhat into aesthetics), so that could be turned off for more usable output energy. I haven't compared converters, so you might find something more efficient.


  Are you sure? yes | no

Daren Schwenke wrote 05/23/2019 at 13:28 point

For the current size a ping-pong ball might work well too, 

  Are you sure? yes | no

Mike Rigsby wrote 05/23/2019 at 13:32 point

Good thought--that would be smooth, light and readily available.

  Are you sure? yes | no

Davinder Chandhok wrote 05/23/2019 at 13:52 point

I recently built a Jetson Nano bot from a tutorial from NVIDIA and they use a 1" delrin caster ball like this one: https://www.exp-tech.de/zubehoer/sonstige/6715/pololu-ball-caster-with-1-plastic-ball-and-ball-bearings
It's smooth and has very low rolling resistance (inherent to the material). I think Sparkfun or Adafruit sell it in the US, and you can also find it on eBay. I found it works very well, even with a 3D-printed caster housing.

I see, I think for those power stats, I'd have to find bigger supercaps, as a Jetson/Raspberry board would draw around 1 A, and the motor driver would also draw at least 0.5 A. In any case, I find your build pretty cool, and I would love to find a way to power mine with supercaps and then recharge every so often with a 10-second bump into a charging station.

  Are you sure? yes | no

Giovanni Carrera wrote 05/23/2019 at 04:29 point

interesting project, I'd like to know the energy [Wh] actually supplied by the super capacitors, measuring current and voltage.

  Are you sure? yes | no

Mike Rigsby wrote 05/23/2019 at 13:02 point

In this specific configuration, my dc-dc converter is set for an output of 7.7 volts.  The robot (Arduino, shield, motors, converter) draws roughly 250 mA. Starting at a charge of 8 volts and draining to 3.5 volts gives me 25 minutes of run time. So, my steady output energy equals 250 mA at 7.7 volts for 25 minutes. If I start at 8.1 volts and discharge to 2.8 volts (questionable bottom limit of dc converter), I would get a little more time.

Here's some information I put together in the past that you might find interesting.

Ultracapacitor or Battery?
06/14/2016 at 17:26 • If you are a hacker, interested in doing things differently, here's some basic information regarding ultracapacitors.

For a fast "rule of thumb" comparison, 1000 farads at 2.7 volts amounts to about one watt hour of energy storage. This means the 3000 farad capacitor above stores about the same energy as the NiMh AA cell pictured above. Using a La Crosse BC-700 charger, I charged the AA cell above (rated at 2500 mAh) at 500 mA--discharged at 250 mA--and recorded a capacity of 2330 mAh. The capacity and number of charge/discharge cycles of batteries depends on battery chemistry and charge/discharge rates.
I took five 350 farad capacitors (in series) and charged them to 12.72 volts. After 24 hours (no load attached), the voltage had declined to 12.57 volts. After 48 hours, the reading was 12.50 volts. Capacitors will lose noticeable charge in a matter of days.
A 30 gram battery (NiMh) is comparable to a 500 gram capacitor. Clearly, batteries are the winners in this category.

Cost--here's an interesting area. First, a little history. In 2009 I purchased twelve 350 farad capacitors and they cost $23.00 each at the time. Today, the same capacitors from the same company (tecategroup.com) cost $10.75 each in quantities of ten or more. So, the cost is coming down. Using our comparison above, a $3.00 battery can be good for 2000 charge cycles--the $44.00 capacitor is good for 500,000 charge cycles. If you had a need to charge/discharge 500,000 times, you would need 250 batteries to accomplish the task ($750. versus $44.00). So, are there any consumer products utilizing ultracapacitors?

Yes--this screwdriver/flashlight charges in 60 seconds and is currently available on Amazon.com for about $21.00. This appears to be a product that was launched for $60. and didn't make it, so don't expect it to be around forever. Coleman made a capacitor powered screwdriver a few years ago (I owned one), but I can't speak to it's long term functionality as I tore it apart for all the good pieces it contained.

Unlike batteries, the voltage steadily declines on a capacitor; meaning that more circuitry is required to keep the output usable.

Ultracapacitor sales do not target hackers or consumers--they are intended for rail systems, trains, utility vehicles; that sort of device. Look at the "bolt" connectors in the top picture. The M12-1.75 bolt is about one half inch in diameter. We're not talking about 300 mA discharge and 10 amp charge rates. These things are designed to move serious amps in a hurry.
That being said, if (like Mato) your goal is to charge quickly and get back into service (hand tools, flash photography, robots, toy vehicles) capacitors deserve a look.

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Mike Szczys wrote 05/17/2019 at 17:45 point

This is really cool. I've been looking for a reason to build something with supercaps and this is it!

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