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This month: a kit review by Dave Kennedy* Students, teachers and grown up kids of all ages have been hanging out for a kit such as this for years: a piece of great design and good engineering, together with a low cost can do the unthinkable… bring FUN back into the classroom! ESCAPE ROBOT KIT 26  Silicon Chip siliconchip.com.au I t’s called an Escape Robot and it does exactly that: manoeuvres around obstacles, weaves its way through mazes and ultimately escapes from entrapment. It can also move, in a seemingly clever way, around and across perimeters, closely exhibiting insect intelligence. Overall, we were very impressed with the package. The completed robot with his seethrough dome cover and battery packs removed so you can see the “works”. We added the extra cell so we could use NiCads or NiMH batteries. How it works The Robot transmits infrared pulses from three points in its front field of view. Reflected pulses are received by a receiver module and the data is processed onboard. Evasive action is then directed to the drive motors with a clever gearbox configuration delivering output to three axles on either side of the robot. It also communicates its intentions with audible beeps. The robot has interchangeable cup wheels or individual leg attachments, enabling a variety of movement styles. The body is encapsulated in a clear bubble and the whole package looks incredibly realistic, in a robotic sense. The robot measures a very credible (for a robot!) 150 x 150 x 120mm. The power supply is 6V via four AAA cells (comments later). Kit quality All of the electronic, mechanical and structural part counts were correct. The electronic parts are of a good quality and the PC board is robust, stencilled and part placements are roomy. The tracks were tested to 370°C without lifting (kids love to cook PC boards). The addition of an IC socket and LED mounting brackets is thoughtful. The structural sections are of the press-out, pre-moulded type and their tolerances in construction are excellent. The motors, gears and axles mount well and include brass bushes. The main base plate has small support ridges on it, which make it easy to orient and stabilise the support panels, and mounts, while you screw them into place. Compared to some of the “educational” kits we’ve often been forced to use, this really is a quality kit. At this stage the spare parts situation is unclear but (apart from the PIC) you should be able to obtain most of the electronic parts from the usual sources, including the kit supplier. Tools required Constructors will need access to a fine tipped temperature controlled soldering iron set to 320°C (something that’s not always readily available in schools) and flux core solder under 1mm. For close-up soldering, safety goggles are required. Miniature diagonal nippers and long-nosed pliers are also “a must”. A Philips #2 driver is needed and it is helpful if it is magnetised. A multimeter is handy for troubleshooting, of course. Kit instructions. He’s turned turtle! Here’s what the underside of the complted robot looks like with the “wheels” option. siliconchip.com.au There are two sets of instructions, one for the electronics module and one for the mechanical construction. Both are of the pictorial kind, using very few written prompts. This is an increasing trend in international kit production and emphasises the increased role of the decreasingly paid technology teachers in our schools. (Stop whinging Dave, Ed.) The pictorials are actually quite good, if you look at them closely, and teachers constructing the kit will be able to make mental notes of the fine implied instructions before the kits are given to students. Some of the mechanical instructions need strong scrutiny, especially August 2004  27 angles to the body of the kit and they produce a surprising grip as a result. The robot moves in a seemingly sliding way on a variety of surfaces. Student skills This kit is not suitable for novices, nor is it a suitable project for underequipped classroom use. Students completing this kit must be already well trained in fine-detail soldering, part identification, construction skills and basic electronics theory. As a guide, my students have completed a basic electronics course at the year eight level for 30 hours. In year nine they undergo a further 30 hours of mainly practical work, before I’ll give them a go at this kit. It also depends on your class size and the ability level of the kids. The bad news The bad news is that the robot draws 300mA at idle conditions and 600mA and more under physical load. This means that AAA dry cells are almost literally eaten by this kit. Don’t give up though, there are solutions to this problem. A simple solution The completed project, disassembled enough so that you can identify the major components/assemblies. Top of the picture is the modified power supply (see next page); centre is the gearbox/wheel assembly and at the bottom is the main PC board with all the electronics. A clear dome covers the finished robot. the motor housing and gear assembly tasks. The best teaching strategy is to remove the instructions from the kits. That’s right, don’t give the instructions to the kids! If you do, some of the idiots (woops, delightful students) will run blindly ahead and completely mess up their kits. Instead copy only the part identification pictorials and give them these sections. You can then go through the parts check list and identification skills prior to construction. One great aspect of this kit is the fact that the electronic part number is displayed on the PC board but the part value is not. This means that you can run the part selection and insertion process in class, literally part for part. Here’s a tip (from experience!): enlarge the electronic and mechanical construction instructions onto 28  Silicon Chip overhead transparencies or A4 paper sheets, using a new overhead or sheet for each step. In this way you will keep the whole class at the same construction sequence and you can control each step of the process. If you have gifted kids who work quicker than the pack, let them act your special helpers or “apprentices” and get them to help the other kids to catch up. Leg and wheel configurations When you construct the robot, the last step is to attach the legs and / or wheels. While the legs produce a very bug-like movement, fitting them permanently is not a good idea. They end up going out of synchronisation under load and the gearboxes may get tooth-stripped. In addition, much more current is consumed. The cup wheels are the better option. The axles are offset at different Get the kids to buy Nicad or even 800mA NiMH (Nickel-Metal- Hydride) AAA batteries. As these rechargeables are rated at 1.2V, it is necessary to add one more battery to the pack in the robot to provide the required 6V. A single battery is easily added beside the 4-pack within the bubble housing. The extra battery must be connected into the negative side of the wiring before it enters the connecting plug on the PC board. Simply cut the black supply lead and splice in the extra battery. (See Fig.1) A better solution Buy a cheap car battery and a cheap trickle charger for the classroom/lab. (You can use these as a power supply for other kits as well.) Also buy a 12v to 7.2V fast charger (around $40; eg Powertech 12V-7.2V <at> 1.5A). Just be careful with battery acid – it can be pretty nasty stuff. A further Nicad is needed in series with the charging circuit to bring it up to the required 7.2V loading for the fast charger. This “dummy” battery is connected siliconchip.com.au WHERE FROM, HOW MUCH? The Escape Robot kit is available from Altronics stores (Perth, Sydney and Mail Order) for $39.95 rrp (Cat K1103) They also have AAA NiMh cells for $9.95 pk 2, (Cat S4742B); single AAA cell holders for 55c each (Cat S5051). Compare this photo to the diagram below when modifying the power supply to use NiCads or NiMH cells. If you don’t do this, the kids will always be buying batteries because the robot really chews through them . . . outside the robot. Charging leads can then be taken out of the bubble at the rear of the robot and fashioned into a “tail.” Fig.1 shows the complete wiring harness. Tech talk The power supply is tapped at 4.5v for the motors. The logic runs at 3.6v via a zener on the 6V rail. This ensures that the logic will not fail as the motors run the batteries down. The heart of Fig.1: here’s how we modified the power supply pack to accommodate the extra rechargeable cell, making the battery pack back up to 6V. The “dummy” cell drops the excess voltage from the 7.2V quick charger. siliconchip.com.au the circuit is a 78P156ID PIC which is crystal clocked at 4MHz. The IR LEDs and the buzzer are switched by NPN signal transistors that are driven by PIC outputs. A single IR receiver unit sends data pulses directly to the PIC. The motors are driven by NPN and PNP signal transistors configured in the standard H pattern on either polarities of the drive motors. They are triggered by PIC outputs. There is no listing for the PIC’s software, so this can’t readily be The Powertech 7.2V/1.5A Quick Charger is from Jaycar; selling for $39.95 (Cat MB-3515). used for any programming teaching. Costings If you haven’t done so already, register your school as a wholesale customer at all of the major suppliers that you deal with. Your costs will be cut by up to 30%! Good luck in construction and have heaps of fun with maze competitions and drag races! Oh, sorry, I meant help the students have heaps of fun . . . SC * Dave Kennedy teaches electronics (among other things!) at Mater Maria Catholic College, Sydney. August 2004  29