Introduction: Weekly Project: Follow Me--the Mobile Beverage Cooler
Invariably, when you want it...it's over there--the cooler, that is, holding your favorite beverage chilled to perfection. Whether you're at the beach, on a picnic, or sitting at home watching a DVD, when you get thirsty it's time to get up and make a round trip to the ice bucket, cooler, or fridge. Rather than making the effort, why not have the drink come to you?
Just Follow Me.
This Mobile Beverage Cooler is built from several odd-fellow discarded surplus components that are reincarnated in a robust remote-controlled platform capable of delivering a chilled drink container to you with just the wave of your hand. Now don't misconstrue Follow Me as a faithful servant awaiting your beckoning call, rather this mobile cooler is a proof of concept platform that can be the basis for a bigger and grander project.
Serving as the foundation for Follow Me is a discounted plastic model tank kit. This 1/25th scale Jagdpanther kit by Academy was selected solely based on price. There is neither actual nor implied endorsement of this German tank destroyer. If you can find another large scale armored fighting vehicle kit, use it.
It's been mentioned in various books and magazines that tank kits from Academy represent one of the best bargains in mobile platform hacking. Two motors complete with gearboxes are mounted in a neat, self-contained chassis. Even if you don't intend to build a tracked beverage cooler, this motor/gearbox combination can be used in a variety of other projects.
Controlling the movements of the plastic model tank are two Passive Infrared (PIR) sensors. Rather than sound an alarm, these motion detectors are modified to trigger a relay that, in turn, activates one of the tank's electric motors. Furthermore, a PIR sensor is independently tied to each motor. Therefore, crude turns and forward movements can be controlled by signals from a combination of both sensors. All is not bliss with Follow Me, however.
There are two significant and limiting parameters that govern the operation of the PIR sensor. First, there is a 15-second delay period following each sensor trigger. Therefore, sudden changes in direction might not be picked up by Follow Me.
A second limitation can be even more stubborn to overcome. Following a trigger by the PIR sensor, the relay is held closed for approximately two seconds. This duration translates into roughly 1-2-feet of travel. If a longer time of operation is desired delay circuits can be added to the relay's output. Instructions for this type of modification are supplied with each surplus PIR sensor.
During testing of Follow Me a range of 10-15 feet was needed for obtaining optimal sensor readings. Furthermore, the sensor is more sensitive slightly off center.
The operational Follow Me Mobile Beverage Cooler is easily capable of transporting a previously chilled drink to you (provided you are patient; remember the speed is roughly 1 inch per second as you wave your hands) or you can opt for adding your own drink chilling system with a Peltier Junction. This optional add-on chiller will require a separate 6.5-12V power source (plus thermal protection and heat dissipation).
Either way, arming your next party with a battalion of Follow Me Mobile Beverage Coolers could give a new definition to getting blitzed.
Step 1: How to Build Follow Me
Difficulty: Hard; requires delicate soldering and complex circuit building
- (1) 1/25th scale Academy Jagdpanther plastic model tank kit ($43.42; Squadron.com #MH1342 ) NOTE: If this kit is sold out; try substituting this Academy Panther-G tank kit; $57.09; Hobbylinc.com #acy1341 or this Tamiya tank kit: Tiger I; $83.85; Squadron.com #TM48202. Beware there is a non-motorized version of this Jagdpanther kit #13019.
- (2) PIR sensor ($5.95; Electronic Goldmine #G4567)
- (2) Coto SPST 5VDC reed relay ($1.00; All Electronics #RLY-475)
- (2) 100mf electrolytic capacitor ($.16; DigiKey #P12919-ND)
- (2) 1N914 diode ($.30 for 10 pieces; DigiKey #1N914-TPCT-ND)
- (1) Beverage "cozy" or "snuggy," holder ($1; various discount stores)
- Scrap perforated circuit board
- Mounting hardware
- (3) "C" batteries
- (2) 9V batteries
- Cable ties
- Peltier Junction cooling device ($7.95; Electronic Goldmine #G2201)
Step 2: Tanks for the Memory
The first step is the easiest--build the model tank kit. Be forewarned, however, you don't need to add all of the armaments and accessories to the model. Only add the amount of detail that you need for a strong, stable mobile platform.
Install the two motors and gearbox inside the tank's lower hull.
Step 3: Looking for PIRfection
Each PIR sensor needs to be modified for driving a relay switch. Instructions for this modification are supplied with each surplus sensor. Use wire leads approximately 12 inches long for this modification.
The control wires for each sensor are routed out the screw hole in the case back. These wires will be added to the relay circuit that you will be building in the next step.
It's a good idea to test the operation of the sensor at this time (see NOTE below). Temporarily connect the two control wires to an LED with a current-limiting resistor. Install a 9V battery and wave your in front of the sensor. The LED should light for approximately two seconds.
If the operation tests OK, the modified sensors are mounted upside down on the top of the tank. This orientation will ensure that the optimal angle of coverage for each sensor is deflected upwards from the tank. Also, the sensors' coverage should have a slight overlap along the centerline of the tank's cross section.
NOTE: These PIR Sensors are surplus equipment. As such, they are sold "as is" and there is a chance that a sensor might not work in this modified capacity.
Step 4: Run a Relay Race
An independent SPST reed relay is tied to each PIR sensor. An electrolytic capacitor and diode help to smooth the on/off operation of each relay by reducing "chatter" on the PIR sensor control lines.
Each relay is also tied to one of the electric motors inside the tank.
The tank kit's remote control box is used for housing the completed relay circuit board along with the motors' battery pack.
Step 5: Motor's Crossed
Using the wire from the tank kit's remote control, wire the motors and battery box to the relay circuit board.
When all of the wiring has been finished, bolt the remote control box to the top of the tank behind the forward-facing PIR sensors.
Step 6: Don't Drink the Water
In the Jagdpanther kit, there is a step or shelf behind the non-movable turret that will hold one 12-ounce beverage can. Either attach an insulated cup holder with your drink or create a can chiller from a Peltier Junction.
There are a couple of safety points to consider when using the Peltier Junction circuit. First and foremost; watch out for excessive heat buildup. This heat can come from both the circuit's heat sink, as well as from current drawn through the battery power source. Make sure that both of these heat sources are insulated from the plastic parts of the tank kit and PIR sensors.
Another point to remember with this chilling circuit is to ensure that there is direct contact between the can and the cool side of the Peltier Junction. There's nothing worse than having a drink caddy follow you around all day with a drink that is too warm to drink.