The question has come up about the different really micro R/C system out there and what makes one better than another. Here are some general pros and cons of the ones that I have played with.
The RFFS was the first sub-2 gram, 3-channel, proportional, plug-n-play micro R/C system. It has a built-in ESC and the directional controls drive magnetic actuators. The actuators are magnet and coil and weigh up to 2 grams and as litlle as a 1/10 gram. A single LiPoly cell powers it. It is wide band and can suffer interference in a crowded environment. I have quite few of them and I love them. If you are so inclined, you can remove the plug-n-play option and remove the pins and hard wire the system. In this dieted form with a light-weight antenna, the radio weighs 1.5 grams, and a couple of stock 1-gram actuators gives a total weight of 3 1/2 grams. Some very small airplanes (like less than 6" WS) are being flown with this gear. In stock form and with the largest actuators, the weight is still only 6 grams. The battery is connected directly and no switch is required. The RFFS with the 'big' BSD actuators is shown in the last photo.
The Micro Joule from Cirrus is a narrow band servo based system with remarkably light weight - some where in the neighborhood of 1/4 ounce. It is also plug-n-play. It had serious problem to begin with, but Cirrus corrected all the deficiencies and enhanced the strong points with even better performance. You can get ESCs for either a single LiPoly or one form up to 3 cells.
The external ESC produces a 3.3 volt output the servos which provides plenty of torque without chatter or over-shoot. You really should add a switch to turn these one; plugging produces chatter which can confused various processors. The ESCs are rated at more than adequate amperage for moderately sized planes. Down side is the larger connectors supplied, which are suitable for plugging into IPS or LPS systems, are a major part of its weight.
The MJ servos are 1/4" square sticks and are easy to mount. Heres one that is being fitted in a 2 ounce stick and tissue Albatross. This worked out well; the servo is strong, smooth, and centers well without jittering. Very acceptable. Down side - cost is rather high, and the output arms are fixed in place; mounting must accomodate this or you need to detact and reattach the arms with glue (older ones) or solder.
The second photo shows Falcon servos. These weigh less (1.7 grams per servo). These use the same pager motor as the MJs and have comparable torque, speed and resolution. The are shorter but wider. The interesting thing about these (beyond being extremely light) is the utterly simple mechanical system, and removal of the mechanical pot virtually every other servos use. A 'Hall sensor and a tiny magnet mounted on the output arm make sensing postion a solid state affair and not subject to vibration or wear. There are only 3 moving parts to the servos. Down side - same price as the MJs, you have to swap the red and black leads if you use them with the MJ RX as shown, and they have no real case so care in handling them is prudent. Updates to the design from a responsive manufaturer has added mounting hole and a third output arm for easier geometry in some cases.
I don't have pix of the next two RXs handy, so follow the links...
The JMP RXs are narrow band, and come in either actuator or servo versions. They weigh slightly less then the MJ, but not enough to matter any. They can be had with or without the mini-jst connetors if you are shaving grams. The JMP has a built in ESC and is designed to run on a single LiPoly. An add-on board allows running on two cells for more motor power. They are about 2/3 the length of the RFFS. These RXs, as well as the Falcon servos, are sold in the U.S. by Bob Selman (
http://www.bsdmicrorc.com/). If you happen to fly channel 33, or have a spectra module, JMP also offer sub-gram RXs... The servo versions plug right into the Falcon servos, but the MJ's leads would have to be reversed here. This system claims to and indeed, appears self tuning a shortened antenna.
The Penta is a 5-channel, narrow band RX designed by Stefan Gasparin or CO2 fame (
http://gasparin.cz/?show=main&lng=en follow the links to products and then micro systems). These are about 2 grams and are smaller than a postage stamp, flat and easy to find a spot for inside a small peanut sized model. They need an ESC, and a number are suitable near a gram. If your want full house with flaps for ~10 grams, this is the way to go. The down side to these is that you are expected to hardwire them for minimum weight or add plugs for the mini-jst's. This sytem is available in the U.S. from Dave Lewis (
http://www.homefly.com/). Dave is also a supplier for execellent light weight coverings and extremely light weight CF tubes. One of my Pentas is going into a full-house, stick and tissue, twin-motor Tigercat scale model with either flaps or LG (can't decide). These are very reasonably priced pieces of jewelry, but the down side is the external ESC required, although this lets size the ESC to the model's need.