3. Materials, Tools, and Skills

Bootstrap is designed to take a maker from using pre-made or snap together projects to building one from scratch (or at least from the most basic commonly available components). As a result, it does not require many prerequisite skills and only a limited access to tools.

The assembly instructions assume no familiarity with soldering. However there are only limited opportunities for making mistakes so it would be a good idea to have completed a few basic soldering tasks as practice before starting on Bootstrap. You will need access to basic soldering equipment. Fabrication is a matter of 3D printing or cutting/drilling by hand or with machinery. You will need access to the tools to use one of those options. It is easy to start over if you make a mistake building the fabricated parts. Programming the Bootstrap follows standard Arduino practice and some starter programs are provided. You will need a computer with the Arduino software installed, the correct drivers for your Arduino Nano installed, and a mini USB cable to connect the two. Making sure your set up can program your Arduino is a good place to start on this project.

In addition to the soldering and programming gear, the tools and supplies you should have available include:

  • a small phillips screw driver
  • needle nose pliers
  • flush cutters for trimming soldered leads
  • wire strippers (the self adjusting automatic type are highly recommended)
  • a multimeter with an audible continuity test feature
  • masking or other paper tape
  • a small piece of thick double sided tape (hot melt glue is an alternative)
  • a 2mm drill bit (or something very close) and drill to ream out screw holes on the chassis
  • batteries for Bootstrap. The basic option is 3 AA batteries, either alkaline or rechargeable. Other variations are possible but battery input to the voltage converter should range from 3v to 5v.

 

Materials

Below are all the materials required to build Bootstrap. In the two cases where there is only once source for an item it is identified. In most cases there are many suppliers and ebay is the cheapest source, although not always the fastest or best quality, as discussed in this post.

Cost figures given are for the part only and are often the per item cost when ordering more than one. They do not include shipping costs (which are generally low when not free). Thus they should be used as a guide to getting  good deal and not as a promise of a precise cost.

 3D printed version


If you have access to a 3D printer, print the chassis, bumper, motor mounts, caster mount, and ultrasonic sensor mount.

3D parts

If you do not have access to a 3D printer, see the bottom of this list for additional materials to fabricate or obtain these parts.


An Arduino Nano. About $4.50 if you buy the cheapest type. The cheap ones will often use a CH340 serial chip, which works fine under Linux and Windows (with additional drivers), but requires additional fiddling under OS X Yosemite (search online for instructions). The fully authorized, most expensive versions use a FTDI serial chip that works fine on all platforms. Avoid a cheap version that claims to have a FTDI chip, these are usually counterfeit and may lock up on use. Some ebay sites list Arduino Pro Minis, which do not have an onboard USB connector and serial chip, as Nanos. You need the USB connector.

arduino


A DRV8835 dual motor driver in Pololu’s carrier package. Available from Pololu.com as item 2135 for $4.50.

motor controller


A 5V voltage boost module. You will find these on ebay listed as “DC-DC Converter Step Up Boost Module 2-5V to 5V 1200mA (NO USB)” for about $2 when buying one. Note that the one you need does not have a USB connector mounted.

voltage booster


A Protostack small prototyping board. This only available from protostack,com as item PB-GE-S1. The board is $2.90 in quantity of one. Protostack charges a $9 flat shipping rate, which is a budget buster if you are just buying one item (but great if you buy a bunch of stuff from them). When possible I am giving these boards to Bootstrap builders to help them get started (email me at bill@robot50.org).

protostack


A 3A 250v/6A 125v Mini Toggle Switch. A SPST (single pole single throw) switch is all you need, but they are often mislabeled as SPDT (single pole dual throw), which is fine.  On ebay as cheap as $0.50.

toggle


51 straight male header pins. You can buy these in a single row configuration (they come in strips of 40) or double or triple rows–it doesn’t really matter as long as you end up with 51 total pins. The triple row is easiest to mount to the prototyping board but a little tape will hold any of them in place for soldering. About $0.50 on ebay.

header pins


A battery holder for 3 AA batteries (open, with no cover). About $0.50 on ebay.

battery holder


A 5v piezo buzzer. It’s necessary to get one that has a diameter of no more than 12mm. As cheap as $0.25 on ebay,

buzzer


A 1N5820 Schottky diode. About $0.25 on ebay.

diode


A 20k ohm resistor. 1/4 watt, 5% tolerance is fine. About $0.04 on ebay.

22k


Two 10k ohm resistors. 1/4 watt, 5% tolerance is fine. About $0.02 each on ebay.

10ks


Two N20 micro gear motors. There are a lot of these out there with different gearing and voltages. You want 6 volt rated motors. Motors with a no load rpm of 300 at 6 volts will be the best compromise of speed vs torque. 400 or even 500 rpm motors could be used but the torque will be low and they will struggle on rough surfaces or with additional weight on the robot.  Be careful not to buy very low rpm motors (often 65 rpm) being advertised for robots unless you want something really slow. 200 rpm motors are the slowest I would recommend. The 300 rpm motors run about $4.50 each at the cheapest (ebay or many other suppliers).

motors


Two 42mm x 19mm wheels with 3mm D shafts. The Pololu wheels, part number 1090, are recommended at $7 a pair (copies can sometimes be found elsewhere for around $4). A set of 3D printed substitutes are being made available, however the Pololu wheels have much better traction and allow the use of encoders that Pololu has designed for them.

pololu wheels


Two subminiature lever arm snap switches. These need to have a lever of about 25mm (1″) to fit. Temco model CN0133 is the most commonly available. About $0.70 each on ebay.

switches


An HC-SR04 (or HC-SR05) ultrasonic sensor. Widely available on ebay and elsewhere for as little as $2.

sr04


A minimum of four female to female jumper wires with Dupont connectors. These can be 150mm to 200mm in length. Usually sold in strips of 40 on ebay for as little as $1. Additional wires will be needed if you add options, so a full strip is handy to have.

jumpers


About 2 meters of hook up wire. Almost anything that can handle over an amp of current at 5 volts will work with the electronics (24 awg solid core is used in the instructions). However some types of wire will work better than others: Solid core wire is much easier to work with than stranded wire. The total diameter of the wire, including insulation, should be between 1mm and 2mm to fit in confined spaces. Having at least two colors of wire will be very useful in keeping things straight.

This is a good place to scavenge a part instead of buying one.

wire


25 each of m2 x 12mm philips head screws and nuts. About $5 for both on ebay,

screws


Nylon hex standoffs m2 x 12mm. Nylon is recommended because most of the metal ones do not have a full length thread and cannot be used as a result. You will need four of these for a 3D printed version of Bootstrap and six for the non-3D printed version. Most often sold in packages of 10 on ebay for about $2.

standoffs


A 1/2″ steel ball for bearings (used in the caster mount for Bootstrap). About $1 on ebay.

bearing


 

Additional Materials for Non-3D Printed Version

If you are not using a 3D printer to make Bootstrap you do not need the steel ball listed above. You will need 6 standoffs instead of 4. You will need to fabricate a chassis from a 6mm x 150mm (1/4″ x 6″) piece of plywood, Sintra or other stiff sheet material using the template available on this site.  You will also need to purchase 3 additional items and fabricate a bumper.


A 1/2″ Pololu metal ball caster. This kit is available from Pololu.com as part number 953 for $2.

pololu caster


A pair of micro metal gearmotor extended brackets from Pololu. These are available from pololu.com as part number 1089 for $5 a pair.

pololu brackets


A mount with a wide base for the HC-SR04. A typical mount of this type, made from acrylic, is pictured. The narrow base tall mounts sold for the HC-SR04 are not a good match for Bootstrap. About $3 on ebay.

ultrasonic mount


Finally, you will need to fabricate a front bumper. The best material for this is a scrap of aluminum flashing (used in roofing and available at hardware stores). The finished piece should be 11mm (.43″) tall and 160mm (6.3″) long. Flashing works best because it is extremely thin and light, can be cut with strong scissors, keeps it shape when bent, yet remains flexible. However other materials with similar properties can be used. Keep it as light as possible to avoid ruining the levers on the switches with too much weight. A trimmed piece of flashing is shown. The bumper can be mounted with strong double sided tape or appropriate glue.

flashing

 

bill@robot50.net