ZMR250 QAV250 Build

[quadfather]

Just a couple of pics of my ZMR250 after its first assembly pass.

Specs
ZMR250 CF Frame with overcraft PDB
Emax MT2204 2300K_V Motors
Emax 12A Simon Series ESCs
Acro Naze with cleanflight v1.50
HQ 5045 Bullnose Props
Turnigy 5V 3A UBEC
FrSky D4R-II RX
SkyZone TS5823 5.8GHz 200mW VTX
Sony CMOS 800TVL FPV Board Camera
Mobius ActionCam
Zippy Compact 1300mAh 25C 3S (to be upgraded)
AUW 535 grams

I successfully managed to forget to take pictures as I went along building it.  So, in a few sentences here';s what I did.

So Far
Trimmed ESC and motor wires to length.  Soldered motors directly to ESCs.

Soldered the PDB (buzzer and video lines).  See observations below.

Assembled the frame.  Nothing special, no magic tricks, simply bolted together.  See observations below.

I would have liked to put the ESCs between the plates, but they are at capacity with the motor-prop combo (12A at full throttle). So I decided to leave them on the arms for better cooling.  In hindsight I should have gone for 18A but I bought all the kit before the bullnose props were available.  It will be fine with regular 5030 props.

Soldered 4x2 straight pins for motor outputs to Naze, omitting the VCC rail in the centre.  Soldered 2x2 straight pins for powering the Naze from the Turnigy UBEC to the remaining two outputs.  The spare power pins will be feeding the Mobius.  Soldered VBAT and buzzer to Naze and PDB.

Naze and RX are set up for PPM to reduce spaghetti, using one regular servo cable soldered to the Naze.

Strapped RX and VTX to the top of the frame.  Final position to be decided.

ESCs are programmed and calibrated.  The Naze had its initial configuration done.






Observations
The pads for the video bus are kind of flimsy.  I managed to delaminate them with a 30W iron. 
Thankfully they didn';t rip off so I CA';d them back to the plate and secured the wires with CA to reduce the load on them.  The bigger pads were fine.

The anodised aluminium standoffs that come with the frame have a slightly larger diameter than the clearance around the drill hits on the PDB.  This can result in grinding away the solder mask on the PDB, exposing the copper layer.  Although the standoffs are anodised I didn';t feel like exposing the copper, so I went with plastic washers between the standoffs/bolts and PDB.






To Do
Determine the final resting place for the RX and VTX.
Cover exposed contacts on the PDB with liquid tape.
Hook up telemetry from Naze to RX.
Tidy up loose wires.
Tune the FC.
Fly!

The CoG is pretty much spot on in the current configuration, I';m just not sure if the battery should be above or below the frame.  My gut says below.  If anyone has some empirical data about the best battery position I';d be grateful if they could share it.

This setup has plenty of oomph.  Hovers at about 30% throttle.    However, the current battery is not up to the task, so I ordered some Zippy Compact 1500mAh 35C 3S batteries.  They will increase the AUW by about 25 grams.

Cheers,

Tim

[JT]

 Tim, re the battery position, underslung is obviously better in theory as the whole thing should be naturally more stable that way, but the thing that keeps mine on top is the speed and hardness with which these little quads can bellyflop being essentially brick shaped! It only takes a sharp stone etc lol.  I have never had any issues with the lipo on top with balance or handling and it just seems a little more out of harms way there.

[Hands0n]

A very nice looking build for sure, Tim.  I do like those boards, they really set off the ZMR250.  Interesting observations, the use of nylon washers to insulate from the posts was spot on. Take no chances

I';m with JT on the LiPo positioning. Something to consider.

[barneyg]

Interesting observations, the use of nylon washers to insulate from the posts was spot on. Take no chances

It was one of the suggested fixed in the rcgroups thread for them - the other being use nylon standoffs.  Apparently the ZMR250 that overcraft measured up had thinner standoffs than the majority of them hence the lack of clearance on the PDB.  the Mk3 boards have more space.

[Beaver2206]

Looking good!

I think you are right with the battery location.

[agrs1974]

Looking the part Tim! Look forward to the maiden.

[quadfather]

Thanks for the comments guys!

Tim, re the battery position, underslung is obviously better in theory as the whole thing should be naturally more stable that way, but the thing that keeps mine on top is the speed and hardness with which these little quads can bellyflop being essentially brick shaped! It only takes a sharp stone etc lol.  I have never had any issues with the lipo on top with balance or handling and it just seems a little more out of harms way there.

I have ordered a small sheet of Kevlar Twaron mesh and intend to make a small pouch for the LiPo.  As you probably know it has excellent abrasion and puncture resistance while still being light(ish) and flexible.  Perhaps it can even be laminated onto a thin carbon fibre box to go around the LiPo for extra rigidity.  I';ll post something once I have played with it.

It was one of the suggested fixed in the rcgroups thread for them - the other being use nylon standoffs.  Apparently the ZMR250 that overcraft measured up had thinner standoffs than the majority of them hence the lack of clearance on the PDB.  the Mk3 boards have more space.

Indeed it was, although the standoffs they were using were a lot larger.  Mine only just touch the solder mask, but I didn';t want to take any chances.  The washers are less than 1 gram.

Can';t wait for the batteries to show up and health to improve.  I haven';t been out in months.