MicroSizers

Of late my kids (5 years old) and I have been messing around with Hobbico MicroSizers, which you can get at various places like Tower Hobbies. They're two-inch-long radio control cars that use pager-vibrator motors, and are customizable with new tires, bodies, suspension components, gears, and motors. They're remarkably fun, which, I suppose, is why they took Japan by storm, and I suspect will do the same here.

Here are some customizations you might like.

Anodized-look Wheels

One of my cars is a red Mitsubishi Lancer Evo VII, so I thought I'd try to give it wheels with a red anodized look. This customization will work equally well with other cars (such as Radio Shack ZipZaps) that have chrome wheels.

To achieve the anodized look I used two coats of Tamiya Color X-27 Clear Red acrylic model paint. This paint sticks to the chrome wheels remarkably well. For the yellow wheels on the Honda S2000 I used X-24 Clear Yellow.

Step 1 - Preparation

Remove the body and tires from your MicroSizer. It's easiest to paint the wheels in-place, still mounted on the car.

Clean the wheels of oil. Make sure they're clean and dry before you begin.

Step 2 - Rear wheels

Paint the rear wheels first. They're easiest. Use a small hobby brush, preferably one with a pointed tip, rather than a flat tip. Use the paint sparingly, or it will clog up the spaces between the spokes in the wheels. If you do clog up between spokes, dry your brush and poke it in there to soak up some of the paint.

For better color continuity, paint the part of the wheel that is normally covered by the tires, too.

When painting the wheel with the drive gear be very careful not to paint the gear itself. The gear is precision-molded to mate with the other gears, and getting paint on it will slow the car down. If you get paint on it, use some acrylic paint thinner to clean the gear off. Do this even if it forces you to repaint the wheel.

Don't worry about painting the backs of the wheels. In practice no one will ever see them.

Step 3 - Front wheels

You'll find it much easier to paint the front wheels if they're not allowed to roll. The easiest way to prevent them from moving is to jam something in from behind, like a pair of hobby tweezers or a toothpick. This also serves to keep paint off the axle, which is important.

Paint the top of the axle pin, too.

Step 4 - Second coat

You'll find the wheels really do need a second coat to look their best. Wait an hour before applying the second coat.

Step 5 - Reassemble and re-lubricate

Give the paint another hour to dry. Relubricate the rear gear and front axels and make sure they both turn freely. Then carefully replace the tires and body and enjoy your new customized MicroSizer!

Blacked-Out Wheels

The black Celica shown at the top of this page was colored using a different technique. Since I don't have any transparent black paint (and I suspect no such thing exists), I needed something that would let the chrome sheen through but still make the wheels look black. After some testing I settled on a Sharpie and it turned out great. You'll have to jam the tip of the Sharpie in between the spokes pretty hard, but it works pretty well. Also, you can use a fine-point Sharpie to get any spots you can't reach with the fat Sharpie.

By the way, the yellow Honda S2000 looks great with the black wheels since it has a black top.<\p>

NiMH Battery Swap

I just put a new NiMH (nickel metal hydride) battery in my Mitsubishi Lancer Evo VII. You can buy them from TinyRC for $4.49. The capacity of these batteries is reportedly 150 maH (milliamp hours), which is roughly three times the charge you'd expect from a 1/3 AAA NiCd battery. The batteries come with no instructions and are completely unmarked. Here's how to install one of these (or replace a stock battery).

(Disclaimer: You perform this task at your own risk. If you're not comfortable soldering, which is what you'll have to do if you break one of the tiny wires beneath the receiver board, then find someone qualified to perform this procedure for you. P.S. Yes, I did break a solder joint when I did this, but I know how to solder! ).

Step 1 - Preparation

Remove the body of your MicroSizer. I also suggest removing the rear axle and idler gear to make it easier to remove the cover over the receiver circuit board.

Now push gently up on the two clips that hold the clear cover over the receiver board at the back of the car. Be careful, because they're not especially burly. Once unclipped, unhook the clear cover and lift it away.

Step 2 - Receiver Board Removal

Carefully lift the receiver board away from the chassis, moving it to the side of the car opposite the idler gear. There are a scad of wires soldered to the bottom of this board, including two ultra-thin wires that come right off the steering coil. (They're so thin the barely show up in the full size picture below). They're very fragile, so be extra careful.

Step 3 - Battery Removal

Step 4 - Battery Replacement

The NiMH battery is actually a little smaller than 1/3 AAA both in diameter and in length. You'll have to bend the two battery clips (see the red arrows in the picture) in about 2mm towards the center of the car so the battery will fit snugly.

The battery I got was completely unmarked and black. There is an ident in the casing on one end of the battery, and that denotes the positive side of the battery. Place the new battery between the contacts with the positive side away from the idler gear.

Step 5 - Testing

Before you even put anything back together, turn on your charger and carefully affix your unassembled car to the charger. Make sure the red charge light comes on and goes off as it usually does. After the charge is complete, remove the car and make sure the motor and steering still work. At this point you can be pretty confident the battery and your installation of it is okay.

Step 6 - Reassembly

Carefully replace the receiver circuit board into its place over the battery. The antenna wire has a knot tied in it, and there's a notch at the front of the compartment under which that knot is supposed to fit. It acts as a strain relief to keep you from accidentally pulling the antenna off the receiver board. Make sure that knot is under the retainer slot before you lower the board into its final position. Replace the clear receiver cover and re-clip it so that it is locked down. I suggest another functional test at this point to make sure everthing is still a-ok under the receiver board.

Finally replace the idler gear, rear axle, and body. Enjoy the extended battery life of your new NiMH MicroSizer!

38,000 RPM Motor

I got a 38,000 RPM motor, which comes from Japan for the Bit Char-G, and have it installed. (The 38,000 RPM motor is the one in the picture with the pink end on it.) Also note that the motor is actually longer than the stock 26,000 RPM motor that comes with MicroSizers. It seems to have lots of top end and not very much torque (i.e. slow acceleration but killer top speed). My goal is to jump my MicroSizers, and I'm hoping that I can find a motor/gear combination that will let a MicroSizer maintain some speed up a hill.

I'll have a report later after I do some tests. (I got this motor from TinyRC for $11.00.)

Grrl Power MicroSizer

We've got a family friend who saw my MicroSizer and was totally into it. I told her mother I'd get her one for Christmas, but she was afraid a mini-RC car might compromise her daughter's femininity. And thus the Grrl Power MicroSizer was born.

I bought a Mazda RX-7 body set and hand-painted the clear body shell with Tamiya Color X-17 Pink acrylic model paint. I also used Tamiya Color X-27 Clear Red on the inside of the taillights, which shows through pretty well. It was hard (for me, at least) to do the detail painting, even with really small horsehair brushes, but eventually I got something that looked pretty good. I have a renewed respect for really talented model painters, of which I am not. Then again, I drink at least 80 oz of coffee a day, and that can't help.

For a final Grrl Power touch, I added some decals. These are actually finger/toenail decals. You can buy them at big drug stores like Rite Aid. They go on well and stick tight, but don't blow it on the placement because they don't come off; instead the just break into little pieces. To protect the decals and give a airbrush gloss to the whole body, I gave it a thin coat of gloss clearcoat. The scary part is that I (like an idiot) used enamel clearcoat, which acts as a thinner on acrylic paint! Fortunately it was a light coat so it didn't do any major damage.

All in all, I'd say this was a pretty effective mod. Only time will tell whether Analyn retains her femininity even in the face of such a masculine gift as a MicroSizer.

Re-crystalling MicroSizers

A current project is an attempt to re-crystal a US MicroSizer with some frequency other than 27 MHz or 49 MHz. Japanese Bit Char-G cars also come in 35 MHz and 57 MHz varieties. Either would be fine - I want to race with both of my kids! Recrystalling the transmitter is easy, but the car itself looks to be a bitch. I'm working on this now.

Recrystalling Update

An EE friend of mine and I have done some analysis and have determined, unfortunately, that the car doesn't use a crystal. There are some false rumors floating around the web that the biggish component at the corner of the reciever board (adjacent to the 'z' in MHz printed on the clear receiver cover) is a crystal, but it is in fact a capacitor. The car seems to use a tuned network (probably an LC network) instead of a crystal, and the variable inductor (the white plastic component on the bottom of the receiver board) is used to tune the circuit to just the right frequency, then the inductor is waxed into place so it won't move.

This is generally bad news, because it's a hell of a lot harder to reengineer an inductive-capacitive tuned network than it is to replace a crystal. I've not given up hope, however. I'm going to try to figure out part of the schematic by following traces on the board and see if we can figure out which components comprise the LC network. If we can do that, we have a chance of doing some microsurgery on the board to change the tuned network's frequency.

Defeat

I have unfortunately decided to shelve the recrystalling project for the near term. I was trying to eek out a partial schematic, but to little avail; the black plastic glob covering the die didn't help. Finally I just bought a Tomy Bit Char-G 57 Mhz car and put my red wheels and body, NiMH battery, and 3.8 motor in it. It's a happy combination. So if you know you're going to be racing with friends with US FCC-approved (27 MHz and 49 MHz) cars, you might consider getting a Bit Char-G at one of the other two frequencies available in Japan. They're identical to MicroSizers and all the parts are interchangeable. The instructions and box are in Japanese, of course, but you didn't need those anyway, did you? If I have time I'll revisit this, but for now my old 27 MHz chassis has been demoted to a parts car. Sigh.

Comments? Ideas? Email me!