Sub 250g 4inch HD Freestyle

By veldros on May 11, 2021

7  272  2

I think this may be the sweet spot for sub 250g freestyle. I have a similar build that's a 3", but this 4" has superior performance.

Notes about the build:
Weight:
This sort of build is hovering right around the 250g mark. This exact build is currently 246g AUW.
There are a few things you can tweak to adjust the weight (x next to ones I did):

  • x Remove 2/4 of the screws mounting the vista unit
  • x Use a battery strap with a plastic buckle
  • x Use a nebula pro camera instead of the dji camera
  • x Use a whoop-style AIO instead of a 20x20 stack
  • Use a lighter antenna on the vista unit. I've seen people say that a dipole still works pretty well, and it would save a couple grams
  • Use a minimortal t or other lightweight rx antenna
  • Use brotherhobby 2004 motors, which are lighter weight
  • Cut some holes in the battery pad
  • Use m2 nylon screws to mount the fc
  • Use a smaller battery, or a 650mah lihv battery
  • Use a naked caddx vista

Flight time (on 4s 650mah):

  • 8m30s flying very lightly in the house
  • 6m30s flying freestyle outside

Firmware:

FC:
I chose this JHEMCU FC because it has some nice features. The rx power is 4.5v so it powers up from USB which is nice for setting things up in betaflight. It also has a 9v pad for the vista. 35 amps per motor is plenty for this build. You could also use something with 25a escs and be fine.

Motors:
This build has lots of power on these 2900kv motors. I'd say anything from 2500-3000kv would be a great fit for this.

Notes about the frame:
One thing I noticed is that all the 4" frames seem to be geared toward the long range stuff and are mostly deadcat style. Also, the frames with removable arms seems to be heavier than a unibody frame due to the extra hardware. So I designed this frame, which is an evolution of the 3" frame I designed before. This one is a squashed x frame instead of true x. I think the squashed x looks better.

Custom frame info:

  • 3.5mm cf bottom plate
  • 2mm cf top plate
  • m2x20mm standoffs
  • TPU for camera/rx/crossfire antenna mount and vista antenna mount
  • 38g including tpu, standoffs, and standoff screws

If there's any interest in this frame, I'd be curious to know. I've been thinking about getting a CNC machine to cut my custom frames. Currently, I have all my frames cut at cncmadness and they do a fantastic job!

I may eventually try to reduce the weight a little so I can get the frame cut in 4mm cf for added strength, and still make it under 250g.

Alternate Frames
I think the Diatone Roma F4 looks nice, or maybe the tomoquads Katana 2. You'll want at least 3mm cf on the arms, and as low of weight as you can get since every gram counts. I'm not sure how these long range deadcat frames work for freestyle as I've never flown one, though. If you try it on a build like this, let me know!

Update
I got a 4mm cf frame cut and am using that now instead. The 4mm frame is 40g including standoffs, hardware, and tpu parts. Still under 250g.

I also tried the pyrodrone 1804.5 motors on a second, similar build. It flies well, but it's less efficient and doesn't have quite as much power. If you want to use a 20x20 stack or full sized dji camera, the 1804 or 1804.5 motors are the way to go. This second build actually has both a 20x20 stack and a DJI cam and it comes in at 248g.

You also may want to consider the smaller motors if you want to use a heavier frame, larger battery, etc

Photos

Discussion

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Madcatmike3d   15 days ago  

I did a search for the Toka 2004-2900kv motors specifically because I'm going to run 4" on them. Well, I'm actually going to run the new 3.5" props on them.. I'm building a modified Acrobrat Duo, with these motors spaced out, enough to fit 3.5" props. I love the acrobrat, but feel like it's limited by the 3" prop size. The plan is to run this motor, running a 3.5x2x3 prop, on a 280g acrobrat on 4s. I was going to run X-nova 1804's, but only have the 5mm shaft version. How do you think these Toka's will turn the 3.5" props?

veldros   15 days ago 

I think the 2004s may be overkill on size/weight. I haven't built a 3.5", but Emax and GEPRC have 3.5" vista builds and they both use 1404s in the 4000kv range, so these tokas may also be a bit low on kv for 3.5". Diatone has a toka 1505 3800kv that may be a good fit for a 3.5" build that's heavier than the emax and geprc. Botherhobby also has a 1504.5 3900kv that may work well.

I can't give any definitive answer since I haven't tried these on 3.5" and I don't have any 3.5" props around to try, unfortunately. I've been thinking about moving my 3" 1404 freestyle build to one of my 4" frames and trying the avan 3.5" props to see how they handle on the 1404s. If I do that, I might have to give them a go on this build with the 2004s as well.

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