# Making tricopter airframe became lightweight

Tricopter airframe of my design result that i posted here is too heavy if setup  using 3 motors. I will use it for Y6 copter because has the robustness . Now, i decided to create a new so lighter weight with a total weight not more than 1kg. This time I should be more careful to calculate the weight and the use of materials. Weight can be reduced is the airframe, while the electronic components and supporting not possibly be reduced. Components that have the assurance of weight is:

1. 3 motor, DT750, @78gram, total: 232 gram
2. Nano-Tech, Lipo, 3S, 2200mAH, 45C Constant / 90C Burst, total: 201 gram
3. Receiver frsky: 9 gram
4. Controller: 9 gram
5. Tower Pro mag 18 ESC x 3 (reflash), @19.5, total: 58.5 gram
6. Silicone cable, connector etc,  approximately: 30 gram

Fix weight will be : 232 + 201 + 9 + 9 + 58.5 + 30 = 529.5 gram

For example, if the planned total weight is 850gr then the rest of the airframe that the maximum weight allowed is 850gr – 529.5gr = 320.5gr.

## Stub

The three arms of airframe materials used alumium piece of 1cm x 2cm box. I plan to make the long arm of the distance between the motor axel and CG is 50cm. Also, Front left and right arm can be folded into the back of the arm parallel to the rear, for easy transportation to the field.

To estimate the weight of the arm by using aluminum box, need to be weighed to obtain density values. Picture on the left, aluminum is 42cm long with a weight 63.8gr. Thus the value of the density of this aluminum is 63.8gr/42cm = 1.52gr/cm if no reduction of weight. Assumed if the extent of reduction of 1/3 the total weight will be (2/3) * 63.8gr = 42.53gr. So the density becomes 42.53gr/42cm = 1.01gr/cm.

Weight reduction should be considered by not reducing the strength of the material. To reduce the aluminum material, i use a milling machine 10mm and 0.5mm.

If the individual requires long sleeves 50cm + 2cm = 52cm, then the total weight before do to weight reduction  wil be 1.52gr/cm * 52cm = 79.04gr. However, if the weight reduction is 1/3 of total weight, the weight will be 52.69gr. So the total weight for the 3 arms will be 158.08gr.

If one arm require long about 50cm + 2cm = 52cm, then the total weight before weight reduction will be 1.52gr/cm * 52cm = 79.04gr. However, if the reduction in weight 1/3 of total weight, the weight will be 52.69gr. So the total weight for the 3 arms will be 158.08gr.

## Reducing the weight of the arm

I can reduce the weight of the arm by making a hole with size 4cmx2cm on one side by using a milling machine.

Arm length is 42cm, the weight to be 35.9gr, still has the strength and robustness. The density will be 35.9 gr/42cm or 0.855 gr/cm, very lightweight. Now the weight down to (0.855/1.52)*100%=56.23%.

For comparison the wooden arm of the weight is 58.4gr 1cmx2cmx60cm size. Then the density is 58.4gr/60cm = 0.913gr/cm. But has the disadvantage can not be reduced weight and easy to absorb water.

So the choice is aluminum as tricopter arm.

## Center plate

Center plate is very important to tie the three pieces of arms in order not changed because no force and pressure and keep the robustness. Of course if you can have a light weight.

Here I use a fiberglass-acrylic with a thickness of 5 mm. The rear arm tied with two 4mm bolts. Two fornt arms  fastened with a bolt that can be folded backward. But I need to add a bolt lock to stop two arms so do not move when flown.

For a while, I did not reduce the weight of the center plate and I would do at the end if necessary. Center plate has a weight of 124.4 grams. However I doubt the strength to hold the arm, if the surface of the center plate is reduced.

## Motor mount

To put the motor to the arm, I make my own mount for the DT750 to be stronger than the original. Of course they are made of aluminum then becomes a bit heavier than the original. However, very strong because it uses the M3 bolts. The two bolts used to hold DT750, one bolt is used for hooking into the arm.  I use this  mount for all three motors.

## Tilt Mechanical of rear motor

On this mechanic, I use a direct connection to the servo shaft with two bearings. In this way, tilt will be a smooth movement. Two bearings mounted in a nylon tube in the two sides.  I use an iron with 5mm diameter, then inserted in the bearing hole. By using aluminum tubes, rear motors can be connected  by using bolts.

## First flight testing

Previously I had never flown a multi rotor, so I do not believe in myself if I could fly this tricopter. I decided just to test if the lift could be stabilized.

## Second flight testing

I tried a second time to be confident.

## Third flight testing

Now I believe myself to fly a homemade tricopter.

Tricopter of my design has a total weight of approximately 1100 grams by using a 2200mAh Lipo. When it began to hover absorbing power about 120Watts or 10Ampere at 12V Lipo voltage.

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## About Bambang Siswoyo

I am a college lecturer since 1988 at UB (University of Brawijaya) in the electronics department. My experience: Applications of Microprocessor system, Applications of Control System, Applications of Field Programmable Gate Array, Computer Programming in computer instrumentations. My hobby: Music especially playing the saxophone, hiking and exploring the countryside.
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