FT Goblin - Lifting capabilities

[PlanlessPlaneMaker]

Hi! I want to make FT Goblin and I made this project for battery pack. It will be my first plane and I don't have any idea if it's overkill. Around 400g battery doesn't feel like it's a good idea, but have heard that goblin has a large amount of lifting power so, maybe it will be possible. I want to use it with flash hobby 2600KV motor

 

[JasonK]

you might have an issue using 18650 cells on the FT goblin.. they have a fairly low max current draw generally.

Can you link the exact motor your planning on using? I suspect at full run up, your going to be pulling to much current for most/all 18650 batteries.

 

[JasonK]

A quick look at the FT goblin store page and it looks like it is using an F-pack motor with a 20A ESC. So to be conserviative, you would want an 18650 cell that could handle 30A draw... many do not. When I went looking for cells for my endurance project, ones that could handle 30A+ ended up with lower capacity to weight ratios... and IIRC started coming in much closer to a standard LIPO pack for power density.

At the very least, you should do some current draw tests on the bench with a lipo to see what type of load your cells will need to be able to handle.

 

[Hondo76251]

I generally prefer to make my own flight packs with LiIon batteries.

These are 18350's (short ones) built as 2s they weigh 50grams. I can series them in the plane to be 4s at just over 100g. With an 1108 motor on a 24" chuck glider i can easily fly for almost an hour.

 

[Hondo76251]

One thing to consider with LiIon, you are generally not flying flat out when going for endurance. In my above setup i went 4s but limited my throttle to about 2/3 in my TX and ended up flying at under 1/2 throttle to maintain altitude.

 

[PlanlessPlaneMaker]

you might have an issue using 18650 cells on the FT goblin.. they have a fairly low max current draw generally.

Can you link the exact motor your planning on using? I suspect at full run up, your going to be pulling to much current for most/all 18650 batteries.

Motor: https://www.banggood.com/pl/Flashho...html?rmmds=myorder&cur_warehouse=CN&ID=511866

A quick look at the FT goblin store page and it looks like it is using an F-pack motor with a 20A ESC. So to be conserviative, you would want an 18650 cell that could handle 30A draw... many do not. When I went looking for cells for my endurance project, ones that could handle 30A+ ended up with lower capacity to weight ratios... and IIRC started coming in much closer to a standard LIPO pack for power density.

At the very least, you should do some current draw tests on the bench with a lipo to see what type of load your cells will need to be able to handle.

By accident I ordered 5A cells... Yeah after some reading i think it's better to go with lipo even despite the price, will have to return them :/

 

[PlanlessPlaneMaker]

One thing to consider with LiIon, you are generally not flying flat out when going for endurance. In my above setup i went 4s but limited my throttle to about 2/3 in my TX and ended up flying at under 1/2 throttle to maintain altitude.

I want to reuse old chinese transmitter so in my case it's not even possible, i will return my 18650 and look for the lipo, if i will find LiPo + charger in my 30 usd budget it will be miracle

 

[Ketchup]

Since this is your first plane I want to point out that the goblin isn’t a very good beginner plane. Something like the FT tiny trainer will be better for learning, it will grow with you and your skills, and it will most likely be cheaper too due to requiring smaller motors escs and batteries.

 

[PlanlessPlaneMaker]

Since this is your first plane I want to point out that the goblin isn’t a very good beginner plane. Something like the FT tiny trainer will be better for learning, it will grow with you and your skills, and it will most likely be cheaper too due to requiring smaller motors escs and batteries.

You're probably right, I already messed up making one goblin and wasted a lot of Foamboard (with next one I will try with laser cutting). I also already brought 2600KV motor and 30A ESC and am not sure if it's the right kind of hardware for tiny trainer

 

[Ketchup]

You're probably right, I already messed up making one goblin and wasted a lot of Foamboard (with next one I will try with laser cutting). I also already brought 2600KV motor and 30A ESC and am not sure if it's the right kind of hardware for tiny trainer

It might not be exactly the right stuff but it will be better than trying the goblin imo. Maybe somebody who has flown a tiny trainer can chime in and say if it can handle the power. I think that on that motor on a 3s it should be fine, but again I don’t know the tiny trainer too well so I can’t tell. Also you should know that telling us the kv of the motor really doesn’t give us much. The kv is only the speed of the motor (measured in rpm per volt, so a 2600 kv motor on 1 volt will be 2600 rpm, and on 2 volts it will be 5200 etc.), we still don’t know the size, voltage, or approximate thrust of the motor with a given prop. The numbers that usually come before kv is the motor size, numbers like 2204, 1806, or in the case of your motor 2207. The first two numbers are the width of the motor in mm and the next two are the height. Also some manufacturers will measure the actual outer motor dimensions and some will measure the motor’s stator. Sadly there is no standard on where to measure from, so as a result some motors with the same measurements can actually be bigger or smaller in size and power depending on where the manufacturer measured from.

 

[JasonK]

Motor: https://www.banggood.com/pl/Flashho...html?rmmds=myorder&cur_warehouse=CN&ID=511866




By accident I ordered 5A cells... Yeah after some reading i think it's better to go with lipo even despite the price, will have to return them :/

unfortunately that doesn't have what i was hoping to see. This is for a different 2207 motor that is 2400kv. If I am reading it correctly that is a 5x4.6 3 bladed prop, so might be over propped from your goblin plan. What I was looking at here is that at full run at 16v (~4s) it hit over 35A draw full open... which is higher then any li-ion pack that I recall seeing. You would definately want a lipo with a good C rating on it.

 

[PlanlessPlaneMaker]

unfortunately that doesn't have what i was hoping to see. This is for a different 2207 motor that is 2400kv. If I am reading it correctly that is a 5x4.6 3 bladed prop, so might be over propped from your goblin plan. What I was looking at here is that at full run at 16v (~4s) it hit over 35A draw full open... which is higher then any li-ion pack that I recall seeing. You would definately want a lipo with a good C rating on it.

View attachment 197439

Here it is for the one i bought

 

[JasonK]

yah, yours shows that even with a small prop, it breaks 20A draw at 4s. which means you would need to make sure your li-ion pack could give 30A (you want some breathing room). Which when I was looking, there weren't many, and the ones that did, tended to have less capacity.