Over the winter, I plan to build a vex drone (or other flying apparatus) out of only non vex pro parts. I suspect that I’ll need to use a low strength gearbox with lexan props, combined with (hopefully lighter?) cortex stuff because
Have a search. There are lots of posts about this, some serious and some less so.
To do this with only VEX parts and Lexan will be extremely difficult, weight will always be your enemy.
A powered glider would almost certainly be your best bet as lack of thrust is also a real issue. VEXnet 2.0 (the later white keys) were better for robots as more robust than the black WiFI versions, but thw range is very short and not really suitable for any kind of flying object. The black keys have a longer range but again, not really suitable for anything that flies more than a handful of metres away.
while cortex is lighter than v5, I think you would get a lot more thrust/weight for v5.
while it may be possible to make a drone, it would be a lot easier if you but the battery and brain on a stationary platform, and had the drone tether to it by the cables, so you don’t have to lift the weight of the brain, battery, or radio. I think you might just be able to fly with 4 v5 motors, but you’d really have to make the drone body super light, probably out of polycarb. and then, you’d need really good propellers, which might not be realistic to make yourself from legal polycarb.
however, I think it is possible to make a flying robot, and I’ve wanted for years to see someone genuinely attempt it.
while cortex is lighter than v5, I think you would get a lot more thrust/weight for v5.
Lets do some math here. In order to fly you need thrust greater then the weight of the motor.
Therefore Thrust/Weight must be greater then 1.
The formula for thrust of a motor can be modeled as:
T (lbs) = pi / 8 * Propeller Diametor^2 * Air density * (Air velocity in - Air velocity out) ^ 2
Assuming takeoff Air velocity in = 0. The maximum theoretical ratio between the tip speed and air flow out can be aproximated as .7, therefore air velocity out =.7 * propeller tip speed (inch/sec)
= .7 * Propeller Diameter * pi / 60 * rpm motor
without a cartridge, a v5 motor is 3600 rpm.
Air density is 0.00237 slugs/ft^3
Therefore:
T (lbs) = pi / 8 * Propeller Diametor^2 * .00237 * (131.95 * D ) ^ 2
The weight of a v5 motor with no cartridge is about W = .25 lbs
Therefore T must be > .25, an ideal ratio is at least 2, so setting T = .5 yields:
Propeller Diametor = .419 feet = 5 inches
So assuming you had a perfectly ideal 5" propeller blade, you could make a drone from v5 motors.
However you only net .25 lbs for each blade, assuming a typical drone distribution of 4, you have 1lb total of carrying weight.
The v5 brain is .63 lbs, and the battery is .77 lbs.
meaning you cannot take off with them.
To carry the battery and brain, 1.1 lbs of thrust per motor would be ideal for the 2:1 ratio.
Meaning using the above formulas, you need 6.2" perfectly ideal propeller blades.
However, the larger the propeller blade, the more drag it produces ad the less efficient it will be.
The stall torgue to the v5 motor operating at 3600 rpm must be examined and compared against the drag of the propeller blade.
At 3600 rpm the torque is ideally .04302 ftlbs
Calculating drag force on the propellar blades is tricky, but can be approximated in as:
T = (.5*D)^3 * ω^2 *ρ *A (note: ω is in rad/sec)
Using a blade thickness of .5 inches: This gives: .125 ft/lbs of drag
Meaning that a v5 motor cannot produce enough torgue at the required rpm to fly.
what if you left the brain and battery on the floor and tethered the drone, so that you only have to lift the weight of the motors and the drone itself?
To go any height at all, you’d need 4 very long tethers. 5 to include a sensor as well. Thats a lot of weight in cable, and a lot of instability.
For that I’m getting .053 ftlbs for the propeller drag, which is still over the max for the motors at .043 ftlbs.
However I am not confident that my calculations were mistake free.
This is close enough you might be able to mod the motors (not recomended) to get more power.
Well my guess is as follows. I haven’t done the math for this because I haven’t taken physics, but if @demonicyoshi is somewhat accurate in his math, I bet it could be done. I think if someone were to essentially completely gut the v5 electronics they might be able to get them light enough that something could work. Also, a pretty rigid frame could likely be built from lexan sheet, spacers, and nylon hardware. As far as making this more viable, I like your idea @Xenon27 about leaving the brain and battery on the ground. Even without useless parts like the plastic cases and the screen they probably weigh too much.
Also Yoshi if this is a custom project why not do electronic mods?
or to reduce weight. the gear cartridge inside seems redundant when you want to spin really fast.
true. it’s more just to see if you can achieve any flight at all, not to fly high.
perhaps a glider would be more realistic?
Only vex legal practices and equipment
Yeah a glider would be fun but I don’t see any good way to mount the brain and battery. Unless I used the old servos, I’d certainly exceed the desired size (<4’)
I would recommend when you test it to not use a radio but a long cord to the brain ( assuming you do a tether drone) to make sure it doesn’t disconnect.
I bet it would because then you could do weight reduction to the greatest extent possible and use leftover weight to your advantage somehow. If you think about it though it also has drawbacks cause you have to have the electronics all mounted and having them stationary isn’t a possible avenue of success anymore.
@NicolBolas I think if you want any modicum of success with this you can’t opt to break only a few of the “rules”. This is really a non-VRC project so it calls for non-VRC measures. I can understand not being able to destroy the electronics though, I personally wouldn’t be that confident doing it and wouldn’t have the money to sacrifice them like that.
I understand but given the constraints of this project, I will adhere to the “rules” or nothing at all. I choose to opt for the first
Ok fair enough. Personally I’d try a glider with huge wings and make sure to avoid the use of metal if you can. It’ll be difficult to fabricate because the materials we use in Vex are not necessarily the most friendly towards fully “custom” builds (in my opinion), but with enough lexan it might be possible to make something that does something.
Have fun. 
If I went with the glider, I think lexan, the old servos, and standoff braces for the wings would be the way to go
not sure you can even run a servo off of v5. also a glider poses a much more serious risk of damage to your electronics than a tethered drone would.
My guess would be the servos run off the same PWM as the MC29 but someone would need to try. Seros probably want 7.2v though to be anh use and the 5V from V5 is less than what Cortex would give.
Realistically, a glider from only VEX parts and lexan is a non starter. A regular RC glider would be balsa and solarfilm amd at least 2m wingspan. Using ally and lexan you’d probably never get lift vs weight in your favour.
probably right.
I still think a tethered drone might be possible with only vex legal parts. but probably not realistic.
unfortunately a drone isn’t really that feasible with purely vex legal parts. too much assembly weight and not enough power. making lexan or alu propellers thatre legal would be a project all on its own
but uh gl
always wanted to see someone try this for the fun of it