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STUDENT HELP

#1
Hi,
I am currently a student and seeking for some help from this forum. My club is asking me to build a heavy cargo lift airplane. For the competition, i only allow to use one kind of dc motor. We got alot of sucess trials last year by using a two stage gear box 4.43:1 ratio. But I want to be able to carry more weight, which we got 320 g last year (the plane has to fit a 24 in circle aka diagonal, length and width has to be 24, not the smartest rule). I want to use the planetary gear box because i found that it has the most torque among most gearbox. Should I use the planetary gear box and will it help me achieve my goal? If any have any other ideas please share. Plssss forgive me if I make any mistake or bad assumption...thank you.
 

buzzbomb

I know nothing!
#2
Honestly, I have no clue what you're talking about. We don't use gearboxes. Everything RC is DC. Exactly what it is that you want?
 

buzzbomb

I know nothing!
#4
hi,
Something like this
This isnt the best set up but it show where and alittle bit of how or why to use gearbox
You've got a prop saver with a very fancy mount on an old DC motor from a stock photo.
hi,
Something like this
This isnt the best set up but it show where and alittle bit of how or why to use gearbox
Ok. That's not a "gear box." it's not planetary. That's just a photo of a reducing gear. So if that is what you want, then just do it.
 

Hai-Lee

Old and Bold RC PILOT
#5
Hi,
I am currently a student and seeking for some help from this forum. My club is asking me to build a heavy cargo lift airplane. For the competition, i only allow to use one kind of dc motor. We got alot of sucess trials last year by using a two stage gear box 4.43:1 ratio. But I want to be able to carry more weight, which we got 320 g last year (the plane has to fit a 24 in circle aka diagonal, length and width has to be 24, not the smartest rule). I want to use the planetary gear box because i found that it has the most torque among most gearbox. Should I use the planetary gear box and will it help me achieve my goal? If any have any other ideas please share. Plssss forgive me if I make any mistake or bad assumption...thank you.
Just a little reminder that the wing area determines how much you can lift for a given airspeed. If you are restricted in wing span I ask if you are restricted to a single wing. Biplanes and Triplanes can give you a massive increase in wing area as well as lifting ability. If no biplanes then a tandem wing design similar to the "Flying Flea", HM14 might offer some lift advantages.

Without motor and propeller specifications and hence the available level of thrust or power it is hard to give any more detailed design direction! If you can supply further details we can provide a more tailored set of recommendations.

Have fun!
 
#8
I love the challenge idea... but a DC Brushed motor? 24 inch size? Get with the times. How about 36 inch circle, single and a twin brushless motor/ESC system with a limit on mah for the Lipo? Or cell number and mah limit. That way you could try out a Mini-Guinea Pig and scratch build a wild heavy micro lifter! Just a thought.
 

Chuppster

Well-known member
#9
Here is the require motor. I actually had test a tandem...It didnt go so well due to the suffer of the amount of drag but it could have been my fault for poorly built. There is no restriction on prop.
I'm not a brushed motor expert, but that doesn't look like a great option for RC airplanes. Regardless, a planetary gearbox should give you a high reduction, but the cost will be more weight and probably more friction. Another thing to consider is that if you reduce the rotation speed too much, you won't have enough propeller pitch to fly. Whenever you convert torque power is never generated, so you'll want to find a gearbox/prop combo that can make the most of your motor. I would suggest keeping with your current gearbox and trying a selection of propellers to see which one suites the airplane the best. If you can measure the current try and get as close to the max current of the motor you can without over-drawing it.
 

d8veh

Well-known member
#10
Those motors don't make much power. What you need to do is use higher volts than it would normally be rated for, which means that you get higher speed and more power with the same current. You then need a gearbox to slow the propeller down to a speed that will be ideal for it.

You need to do some tests to find out how much voltage the motor can take. It's the current that will burn the motor. When you load the motor, the speed goes down and the current goes up. You have to adjust the load to give the speed that gives the current high enough to give the optimum power, but low enough not to burn the motor.

The higher the voltage, the more current you get at the same RPM, but by letting the motor spin faster, you can reduce the current because current is inversely proportional to speed.

A single stage planetary gear system could be used for a reduction range of something like 3:1 to 15:1, but I don't think it would be as efficient as simple pinion gears. If you do decide that you want planetary gears, you need to look for high quality ones.
 
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JTarmstr

Well-known member
#12
Hi,
I am currently a student and seeking for some help from this forum. My club is asking me to build a heavy cargo lift airplane. For the competition, i only allow to use one kind of dc motor. We got alot of sucess trials last year by using a two stage gear box 4.43:1 ratio. But I want to be able to carry more weight, which we got 320 g last year (the plane has to fit a 24 in circle aka diagonal, length and width has to be 24, not the smartest rule). I want to use the planetary gear box because i found that it has the most torque among most gearbox. Should I use the planetary gear box and will it help me achieve my goal? If any have any other ideas please share. Plssss forgive me if I make any mistake or bad assumption...thank you.
Does it have to be any type of motor? 24 inches as stated above is far from ideal but there are a few work arounds. First you could make it possible to disasemble the wing so its larger. Second if you can use any DC motor you want, why not use a brushless 1806 motor? You will have plenty of power and can lift a ton.
 
#13
I love the challenge idea... but a DC Brushed motor? 24 inch size? Get with the times. How about 36 inch circle, single and a twin brushless motor/ESC system with a limit on mah for the Lipo? Or cell number and mah limit. That way you could try out a Mini-Guinea Pig and scratch build a wild heavy micro lifter! Just a thought.
Yeah I didnt write the rule so....
 
#14
I agree the of size of the plane and motor are far from ideal BUT that is the assignment. How much weight can a plane carry given the limitations.

320g sounds like a VERY IMPRESSIVE accomplishment. I would like to know more about how you did that.
We actually got 540 g but it way too inefficient.
 

DamoRC

Well-known member
Mentor
#16
I think we are probably still missing some info on the rules.

We know you are limited to a motor and a craft that fits into a 24 inch circle (i wonder if a flying wing would make the best use of this space).

Are you limited in battery? Is one specified in the rules?

Are there rules on how long it needs to fly carrying the cargo?

I think sticking to the simple pinion gear setup and optimizing the prop is the best option. More complex gears setups will likely be heavier and add friction to the drive system.
 

PsyBorg

Wake up! Time to fly!
#19
Hrmmmm... i would think more along the lines of the dormiers. Run a long solid shaft so you can prop the front and rear of the plane with one motor.

Find a happy reduction gear that can turn two props (most likely lower pitch or even smaller size)