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Old Aug 16, 2004, 04:02 PM
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A Primer on Micro R/C Models

Here is a write-up I started some time ago. It was supposed to have pictures to go with the text but because of a recent promotion I lack the time to finish it. Hopefully the text will speak for itself. Please remeber that what I express here is purely my own opinion. Hope someone finds it useful. Here we go:

A Primer on Micro R/C Models

What is a Micro R/C Model? Hard to tell; if you are used to scale gas models you might consider something like a GWS Pico Stick micro. In my book a model is "Micro" if it weighs around 1oz and uses only one Lithium Polymer cell. I will be base this primer on that definition. Why? Because experience has taught me that a 1oz model is a practical size and can be built and flown succesfully with off the shelf componenets. Components are available for even smaller/lighter models but for each gram you shed the price goes up and so does the need for skill required to make it work well. The 1 cell limitation is chosen because most receivers and motor/gear combos are optimised for this.

How to get started in Micro R/C Planes? Easy: Spend some money. You either buy everything you need or make it yourself. Making it yourself takes time. Assuming time=money it's going to cost you either way. If you are completely new to the hobby the initial investment can seem daunting but there are not too many corners that can be cut and saving a buck or two in the beginning might actually be a bad idea. More about that later. Below I have tried to compile a list of the components you need to get started. If you are a seasoned modeller you might already have a lot of equipment you can use and scratch these components from the list. In the list there might be components that you are not familiar with but don't despair all shall be revealed.

Transmitter
Receiver (JMP, RFFS)
Actuators
Motor
Gearbox
Propeller
Cell(s)
Charger
Model
Misc
Tools


Transmitter

A basic 4-channel FM transmitter (TX) can be bought for as little as $28.00. Strictly speaking it is all you need to succesfully fly a model. However I often tell people to buy a slightly better transmitter with more features, preferably a computer TX. If you get bitten by the bug and stay with the hobby chances are you will end up buying one later on anyway. If not, the better TX is often easier to sell because extra features are in higher demand. If you are on a tight budget, looking for a used TX is not a bad idea but be warned that you might have to buy new cells for the TX. The price you pay should reflect this.

Receivers

Get what is known as a combo receiver; this type has a built in ESC (Electronic Speed Control) and outputs for 2 or 3 actuators. A receiver intended for servos can NOT be used directly with actuators. The choice is limited to and RFFS from Dynamics Unlimited or the Combo from JMP. The JMP is narrowband and works if there are pilots on the adjacent channels. The RFFS needs a couple of channel on each side to be free. I am the happy owner of three JMP receivers and recommendend them. I have never tried a RFFS but I know there are many satisfied users.

Actuators

Most people know what a servo is since it is used in both R/C aircraft, cars and boats. A servo consists of a motor, a geartrain and drive electronics with some sort of motional feedback. An actuator is a very different beast. Basically it consists of a magnet in a coil. When current is applied to the coil the magnet moves. I wont go into lenghty details about actuators here because it is well covered here:

http://rcgroups.com/links/index.php?id=4051

For starters I recommend buying some of the commercially available actuators they work well for others and will work well for you too. If you want to make your own it is well documented how to do so but better to get something flying first.

Motor

My motor of choice for a micro in the 1oz category has to be the M-20 LV motor. It is also known as the KP-00 (KP-00 is actaully the name for a complete unit with both M-20 motor and gearbox but the name is commonly used for just the motor). It is light, robust and combined with a gearbox it packs a lot of punch on just one cell. The motor is inexpensive but there is an even cheaper alternative. This is the N-20 LV motor that can be bought from surplus mail order companies for as little as 49 cents. It is a little bit heavier than the M-20 motor but it can be used direct drive so you save the weight (and cost) of a gearbox. In a light, sleek model the N-20 works really well. However my fist choice would still be a geared M-20. It has the extra power needed if your model is a gram or two overweight. A geared motor can swing a bigger prop and this tends to be a more efficient setup.

Gearbox

Assuming you decide to use an M-20 motor you are going to need a gearbox. There are several choices available as listed above. For an alround model I prefer a 3:1-4:1 ratio. Propped correctly this gives good thrust and duration. Higher ratios and big props are for large, slow models. If the gearbox has brass or bronze bushes, make sure to lube them with a very light oil gun oil seems to work well. Any binding in the gearbox robs power.

Propeller

Now it starts to become difficult. My best advice here is: Ask the vendor what prop he recommends for the motor/gearbox you chose. He will know what works best. If you decide to try different prop sizes I strongly suggest that you get an ammeter so you can measure current draw. You want to stay below 1 amp any more will harm both motor and cell.

Cells

Cells ranging from the 145mah to the 250mah Lithium Polymers are great for micros. They can handle fairly high discharge rates for their size and are quite inexpensive. Get a minimum of three cells than you can fly while the other cells recharge. Buy the cells only when you have a model that is completed. Why? Because the cell can account for 20-25% of the finished weight of your model and can be moved around to acheive the right Centre of Gravity. If you built a short nosed model and find that it needs an extra bit of weight in the nose to balance you might as well make this useful weight in the form of a larger cell. In this case get a 250mah cell instead of a 145mah cell. After a change of receiver in one of my models I actually found that I had to use the larger cell to acheive balance. Since there was no net increase in weight (I switched to a lighter RX) I now have longer duration. Don't worry about duration with the small 145mah cells. If your model is not excessively heavy you should be able to fly on -2/3 throttle and get close to 15 minutes duration. Pretty impressive for a cell weighing under 4 grams!

Charger

Since you only need to charge single cells there is no need for a zillion bucks computer charger. Get one (or several) that will charge one cell at the correct rate. You need a 12volt battery or a 12volt power supply for the charger. Since small cells charge at low currents a 12 volt plug-in transformer will do. Make sure it has a stabilised output and can handle at least 1 amp output in case you decide to use two chargers.

Model

Build or buy? Plans, kit or ARF. There is a growing selection of plans and kits available in this size and even an ARF on offer. Whatever you decide, get something that is tried and tested. Don't make it hard on yourself. That 1/72 scale model can wait until you have a bit more experience. Several vendors offer entry level kits.
A simple sheet or "stick" model is easy to build and prepare for flight. It is also easy to repair. Small models don't break often though the low weight makes most crashes a non-event. If you are on a budget and already have some building skill there are free plans available. I would shamelessly suggest that you take a look at one of my designs; the BUMP. It can be built from a range of materials and is very simple to put together. It is easy to fly too. Look here:

http://www.rcgroups.com/links/index.php?id=4392

Misc

Unless you bought an ARF model there are still a lot of components to consider: Wheels, pushrods, clevises, control horns, hinges, plugs etc. This goes for all R/C models our components are just smaller and lighter. Good kits should includes instructions about these parts they might even be included. If not, make them yourself. Control horns can simply be cut from paper double it up and harden it with CA glue. Holes can be made with a pin. Pushrods are best made from thin carbon rod and should have wire Z-bends at both ends. Hold these in place with small dia heat shrink tubing. Z-bends used in the actuator output arm need to be made from a non-magnetic material like brass, copper or bronze wire otherwise it will disturb the controls. Hinges can be sewn, made from narrow strips of thin plastic or made from beverage can alu and music wire. Micro plugs are available but you can also make you own from connector strips or even from pins and sockets liberated from old computer cables.

Tools

Some essential tools are:
Soldering iron (25Watt is suitable) and solder
Hobby knife
Steel ruler (if you cut your own parts)
Tweezers
Small fine grade sanding block
Masking tape (great for holding parts together)

Conclusion

So far so good. Some might think that the initial investment is high for such a small model but believe me; there is nothing "small" about the amount of fun you will have. In the long run it is probably cheaper to fly micro models compared to larger models. You don't need fancy charging equipment and monster battery packs. Motors and gearboxes are relatively cheap. Models can be built for pennies if you build from plans. Downside is that micros can't be flown outside if there is any wind. I don't have easy access to an indoor site but during summer I take advantage of the long evenings and fly outside when the wind dies down. Micros need little space to fly in and don't make much noise.

One you have been bitten by the bug there are many areas to explore. You might decide to make some of your own equipment or design your own models. You might decide to build something smaller and lighter. Everything is possible. Far too much to cover in this primer. Luckily there is a great source of information: The "Indoor and Micro Models" forum on rcgroups.com all us "lost souls" hang out there and are happy to give advice and exchange ideas.

For a listing of vendors look here:

http://www.rcgroups.com/forums/showt...threadid=55653

Happy landings

Michael Henriksen
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Old Aug 17, 2004, 02:54 PM
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Rogerdoger's Avatar
United States, CA, Clovis
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A Primer on Micro R/C Models

Michael,

Thanks for the Primer!

The information is great and well thought out. I am interested in the smaller micro planes and this has been good to read. I saved the file, too.

Thanks Again,

Roger
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Old Aug 17, 2004, 04:20 PM
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Thanks Roger, glad at least one person likes it

It is all too easy to get engulfed in the race to make smaller, lighter models all the time. The type of model I describe is really becoming the parkflyer of micro flight but it is a recipie I have used often and it works well. There are many others who got their wings in micro flight with similar setups.

Michael
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Old Aug 17, 2004, 04:23 PM
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I like it too Michael!!
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Old Aug 17, 2004, 04:26 PM
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You don't count Graham. You know I know where you live now, remember! Too scared to say anything else

Michael
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Old Aug 17, 2004, 05:36 PM
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and about me???...I like it too...you said you had this article (why you did not published before ), thanks for share it, new airmodelers can understand with a simple explanation wath micro model means , because the magazines only publish some thinks, not all in indoor and micromodels

Thanks,

Alfredo Rubio
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Old Aug 17, 2004, 06:55 PM
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Thank you Michael. Being new at this I like to hear opinions from the experienced guys.
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Old Aug 17, 2004, 08:25 PM
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Fairfax Station, VA
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Michael,
Very informative post! Very good for explaining what makes these micros tick. Maybe it will inspire some to get involved in the hobby, and help some to achieve the success that I struggled for. Your article likely would have saved me the better part of 3 months of trial and error. That is how long it took me to get the first successful bit flight. What a feeling of accomplishment! Probably most are not as patient and persistent as us "lost souls".

I now have 2 JMP Combos which are my preferred rx's as well. I make my own actuators and all my aircraft are built using plans and ideas mostly from ezone, trimmed, modified, and repaired as necessary.

Thanks again for sharing this,
Al
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Old Aug 18, 2004, 02:18 AM
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Cannes Mandelieu, France
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coural combo

michael,
i am the happy owner of a coural combo (and a rffs 100 too!)
the new model is narrow band and very large range.it's also the lightest combo(except the nick one which is incredibly small and light,but expensive!)
patrick
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Old Aug 18, 2004, 05:40 AM
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Deer Park, Tx, USA
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I'm curious whether micro R/C = indoor, since 1oz seems little light for outdoors even with little breeze. I've been trying to identify model appropriate for taking on business trips, but useflu outdoors. Most recent issue of RC Microflight has plans for 0.75 oz 16" span that would seem attractive. I'm gathering that something like a diddle bug ( ~ 3oz ) using conventional servos would not be considered a micro RC plane
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Old Aug 18, 2004, 05:58 AM
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Michael,
Nice work, should be a sticky and stay at the top of the forum .
Stewart
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Old Aug 18, 2004, 08:04 AM
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Michael,
Great article.
This is just what is needed to direct 'new' people to, to get them started in micro models.


The other Graham
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Old Aug 18, 2004, 04:58 PM
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Russel2, take a look at the Micro Mite thread. This little model can actually fly outdoors in a little wind. I used to fly outdoors a lot when I had a garden but only in the evenings when the wind had died down.

Michael
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Old Aug 19, 2004, 09:38 AM
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Joined Jul 2004
2 Posts
Thank you for this and all the other advice you have given. It encourages us technophobes to give micro RC a go.
I'm building Michael's design" BUMP", not difficult even for a newbe like me. If anyone out there needs actuators, Michael produces miniature works of art.
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Old Aug 19, 2004, 01:44 PM
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Leicester England
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I though it was terrible
It was just about toy planes? Where are the jokes, fashion tips, gossip, speling misytries, .... nice pictures ??

Come on, be critical and make the world a better place next time around

In Aeronutz land we never agree about anything (and I am allways proven right in the end) but thats not a personal critism its just a differnet way of looking at things

Lateral thinkign makes for quicker design progress

Mark
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