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CranialRectosis' Twitchity Mini-Tricopter build

cranialrectosis

Faster than a speeding faceplant!
Mentor
#1
So I got one! I have long been thinking about miniaturizing my BatBone but you can only make a Bat so small. Twitchity has a carbon fiber (or G10 version) mini-tricopter that is 200mm and weighs 71 grams. This copter can handle 6" rotors and 22mm motors and comes with a camera plate and cage for FPV.


These are current specs now as of April 2017. It's been in the air now since 12/2014!
The Parts

Frame: This is a Twitchity mini-tricopter frame as shown for the first time here:
http://forum.flitetest.com/showthread.php?12621-Mini-Tri-Test-Build&highlight=twitchity+test

These kits are a custom order through our very own Twitchity. These are not for beginners, but if you have a copter or two built and flying and are looking for a sweet challenge, this is a fine kit.

Flight controller and ESCs:
The flight controller is an RC Explorer F3FC racing.
PDB is the Baby PDB.
ESCs are the Aikon SEFM 30A V2.

Motors & Rotors:
I went with the SunnySky X2204 2300kv from BuddyRC.
Rotors are HQ 5046 3 Blade props from Aloft Hobbies.

Receiver:
The receiver is the FrSky XSR from Aloft hobbies.

Camera and VTX:
The camera is the Foxeer HS1177 from Surveilzone.
The VTX is the mini 2.5 at 200mw also from Surveilzone similar to this one but more power.

First thoughts:
The machine work and quality of this frame are impeccable. Everything fits. The booms on this are 4mm, the frame plates are 1.5mm. After years of flying and crashing the frame shows few signs of wear. There are some chips and I had to use CA on the edges to keep the laminate together, but she's sturdy and flies like a dream.

What an incredible machine. I have dramatically increased the power and upgraded response. I went from PPM to Sbus from 3S to 4S, upgraded the camera and am able to change the tilt on the fly with a screwdriver.

Current PIDS:
TwitchPids.jpg

All up weight is now 452 grams.

Current Photo:
P6150003.JPG
 
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cranialrectosis

Faster than a speeding faceplant!
Mentor
#2
For starters, I received my first set of 3D printed tail pivots from Mustang via USPS late when USPS lost and smashed my package. It almost looks like they put a cigarette out on the box...

P2240001.JPG

This box was DESTROYED. I was apprehensive opening it. Mustang sent me two pivots. One was broken, the other was not. These pivots are designed to hold the servo in place on your boom. The one shipped with the servo could not be broken by USPS. To me that says TOUGH! :)

P2240003.JPG

I am just glad to get my goodies. The broken pivot is glued back together with some Gorilla CA Gel that should hold it pretty well.

Next I opened the Twitchity box and weighed the contents. This is a fine pile of carbon fiber here:
P2250001.JPG

I am not going to build this copter to fly FPV today so I am using some smaller standoffs. This will give the copter a lower profile and will give me less room to hide wires and stash stuff. I am also using female to female standoffs. This allows me to buy long nylon screws and cut them to length as I see fit and re-use the standoffs for multiple builds.
P2250002.JPG

Once the four flight controller mounting standoffs are on the center plate, layout the bottom plate with screws and booms. These booms have a top and a bottom. Line up the motor mount holes before you attach the booms! :)

At this point, I like to put some painters tape on the cutting mat to show motor direction and number and also I put some tape on the screws to hold them in place.
P2250005.JPG

This shows me the limits of my wiring harness. Once the bottom plate and top plate are bolted down on the booms, the gap between plates is only 4mm. IMO, this is a moderately challenging build if only due to the space you have to put stuff. :)

I like the Soma method of building harnesses (videos at the bottom of this page). I am using 16awg wire for the lipo connector and 20awg wire for each 12v rail. The split is 6 to 1. 1 is the 16awg power coming in. I split 6 ways on a tricopter. 3 motors, 1 Naze which will go through the Pololu, 1 for 12v LEDs because who wants a copter without lights :D. 1 for VBAT voltage detection on the Naze (JST). I use heat shrink to hold the pre-tinned wires in place as I solder the nut. Then I remove the heatshrink, clean up the solder job with a file and alcohol and put a tiny bit of heat shrink over the joint.
P2260011.JPG P2260012.JPG

While I am waiting for my Pololu and the ESCs, I painted the LED strips and XT60 connector black with a sharpie and have painted them with clear enamel. At this point I like to connect a lipo to ensure I haven't done anything really stupid. I find this saves ESCs and motors from some of the dumbest things I could do. :)
P2260014.JPG

Waiting for clear enamel to dry.
P2270017.JPG
P2270015.JPG
 
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cranialrectosis

Faster than a speeding faceplant!
Mentor
#3
I have been playing with the tail pivot mount and some sleeving today.

First, the servo wires are too long and I want red wires for my red and black copter. Here, I have removed the back from the servo and replaced the signal wire with a red Arduino wire from Amazon. I then put all three crimped wires into the 3 pin dupont connector, and sleeved the resulting servo cable with red paracord.
P3010008.JPG

I then attached motor lead extensions to the SunnySky, sleeved them in heatshrink and red paracord in preparation for the ESC.
P3010009.JPG

I pulled all the wires through the middle frame hole which is under where the Naze32 will sit.
P3010001.JPG

I set up my Naze32 with the pins on the underside of the board. I am using FrSky and a D4R-II receiver instead of a lemon sat so I soldered a shortened, sleeved servo cable to the Naze32 and will attach the receiver to the underside of the top plate.
P3010002.JPG P3010003.JPG P3020004.JPG

I have since moved my D4R-II receiver from the underside of the top plate and have two sided taped it to the top of the Naze32. I had to do this to move the battery strap on the top plate forward enough to hold the lipo in place forward enough to balance the tail.
P3100001.JPG

Now with failsafe on the receiver tested, I am ready to complete the build.
P3100002.JPG

I started work at 2 Am today. It is now 21:10 and I have another early morning tomorrow. I have no idea if this will fly. If I get a chance I will take this outside for a spin but it snowed all day here today and the high was 4*F. Yeah....4. :(
 
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Twitchity

Senior Member
#4
Twitchity has finished the carbon fiber so I don't have to spend an hour wet sanding the kit and the edges don't cut my fingers or the servo wires.
I probably shouldn't give my secret away... The only finishing I do to the edges is run them across my jeans to remove any residue from the tape when the pieces were being cut ;) The CF and the diamond cut tip bits I use seem to make my life easy as far as the finish goes.
 

cranialrectosis

Faster than a speeding faceplant!
Mentor
#5
So, on another thread, I mentioned the 1A Pololu regulator. I had planned to power this copter's flight controller and receiver with the 600mA Pololu but it was recommended against due to the tail servo.

I also have a Suppo ubec that's good for 3.5A but it has a HUGE capacitor.

Other than amperage and size what is the difference between a ubec and a voltage regulator?

I would love to put that little 600 in the 4mm gap between the plates but I really don't want to start my desk on fire again :black_eyed:.

Anyone have any ideas about how to test my servo's power draw?
 

jhitesma

Some guy in the desert
Mentor
#6
a UBEC is just a voltage regulator that's setup with connectors and form factor RC hobbyists are already comfortable with ;)

Testing the servos power draw isn't that hard - assuming you have a multimeter that can do amperage. You just have to wire it in series with the load you want to test (and on some multimeters you'll have to plug your probes into different holes on the meter.)

So you'd basically pull one of the two power wires for the servo and connect it to one of the probes on your meter then connect the other probe where the wire connected. Then power it up and put some load on the servo since that's usually when they draw the most current.

A multimeter with a peak hold function is best since then you can easily see the max draw. Otherwise you may just have to watch carefully.

Here's a good general video on using a multimeter (including reading current):
(BTW - this guy has a ton of great electronics videos many of which are useful for RC hobbyists.)

And a slower paced one on just measuring current:
 

jhitesma

Some guy in the desert
Mentor
#7
I probably shouldn't give my secret away... The only finishing I do to the edges is run them across my jeans to remove any residue from the tape when the pieces were being cut ;) The CF and the diamond cut tip bits I use seem to make my life easy as far as the finish goes.
This CF really is neat. The matte finish is unlike any other CF I've seen. And the cutting quality Twitchity has pulled off is top notch! It almost doesn't even look like CF with that matte finish, I had to pull out my multimeter to make sure it's actually conductive. (Interestingly enough whatever they do to get the matte finish insulates the top/bottom well enough I wasn't able to get any continuity across it even after making small scratches. The edges on the other hand are extremely conductive as expected from CF.)

I'm probably still going to give the bits that showed up today a once over with some wet dry 600 grit just to be safe. Could probably get by without it...but it will be awhile before I can pull off motors and ESC's for it so I'm in no big rush and it will give me something to do while I save my pennies ;)
 

Twitchity

Senior Member
#8
Well seeing Cranial start his build motivated me to start to build my CF tri. Since he got my personal tri I had to dig around in all of my scrap pieces of CF to get a new one cut for me (thankfully I had just enough). First up was creating the tilt mechanism and a fellow forum member, mpbiv, was kind enough to create a CAD model I could use to 3D print.

Here is the 3D print right as it completed still stuck to the bed. I'm using a Printrbod Simple 1405 for my 3D printer, and I must say I'm extremely pleased with the quality of the prints for the price I paid for the printer.


And here's the tilt mechanism sitting on the arm with servo installed.


And a timelapse of the 3D print. Not the easiest video to watch since I don't have a camera small enough to attach to the bed.
 

Twitchity

Senior Member
#10
All credit for the tilt mechanism goes to mpbiv, I just hit a button on my computer to tell it to print. He was the one that designed the tilt mechanism. The tilt was printed in two different pieces, the base and the motor mount, and uses a 3mm screw to hold it all together. The motor mount has splines build in for the little Turnigy servo I'm using. The plastic inside the hole is support material to help keep the round shape of the hole. Without using the support material the hole would droop and the bolt wouldn't fit through the center. I still have a lot to learn about 3D printing.

Cranial, is your tilt made from ABS or PLA? I've already broke one of the servo walls on the base while trying to pry it off of the print bed. Mine is PLA so it's rigid and brittle.
 

jhitesma

Some guy in the desert
Mentor
#11
Can't wait to see both of these builds in the air :)

Those printrbot's look like a great deal. If I hadn't gotten distracted building quads I'd probably have my own homemade 3D printer by now (that was what I originally bought the arduino mega that got hijacked as my first FC for!) Just the cost of motion control hardware that's kept me from pursuing it further still. But I do have a few big printers in the yard waiting for me to strip them for parts and they should give me the rails and bearings I need...if I ever find time for that project. I also backed the Peachy on Kickstarter but as with most kickstarter projects it's behind schedule. I was originally scheduled for delivery last July but the latest estimate is now next March though I'm still skeptical that they'll make that deadline. The latest prints they're doing are looking really good and I'm in the first group for delivery so fingers crossed :)

When I do eventually get a 3D printer first functional thing I'm printing is a clip to hold my LRS antenna to the handle on the back of my TX so I can ditch the tape I'm using and actually remove it when I'm not flying LRS :D
 
#12
Cranial, is your tilt made from ABS or PLA? I've already broke one of the servo walls on the base while trying to pry it off of the print bed. Mine is PLA so it's rigid and brittle.
They were printed in ABS. ABS is a little more forgiving when it comes to impacts and flexing before snapping. Through making a few parts on the racing quad, I found 4mm wall thickness to provide the needed durability. I also print these parts with a 100% infill.

By the way, I just sent you the STL files to the latest version I printed and sent to Cranial this week. This latest version has a larger center hole (8.5mm diameter) to provide clearance for Sunny Sky motors, and it adds a recess for a nut to sit on top of the base as a screw runs up from the bottom to cinch things down.
 

Twitchity

Senior Member
#13
Thank you, Mustang. I got the files this morning and will be printing out a few to test out as well. My next upgrade is a heated bed for my printer so I can print in ABS, but first I want to make a larger printer and transfer all of the electrical components. I really like this guys design for a RepRap style printer and I'm thinking about working on printing out those parts to make one for myself http://www.thingiverse.com/thing:41967.

I don't want to fully hijack Cranial's thread with my build, but I'll give a little update as I can't have him beat me to a fully assembled tri :) Cranial was kind enough to supply me with some KISS ESCs since he kept having them burn up on him so I wanted to give them a try on my build. Since I don't have a PDB for this frame, and I don't have an external BEC, I started to take a look around to see what I could possible use. Well as I saw a pile of EMAX 12A ESCs sitting on the table I thought to myself, why not? If the tri flew fine with the ESC powering the motor and FC/servo, it should do just fine powering the FC/servo so I removed the motor wires, removed the capacitor, and soldered on two little wires for the 5v and ground. I'm sure it's not the most effective in terms of cost/performance, but it was there and free.



Next I threw on some heatshrink and it sits nicely between the rear standoffs and most importantly, it flies :)



That's it for now. I still need to install all of the FPV gear but she is in the air and flying. I need to tune the PIDs since I'm still running the PIDs from the EMAX ESCs and there is a noticeable jitter coming from the tail servo. It kills me to put those DYS 1806's on this frame, but I'll have to wait until after the holidays to upgrade to 2204's.
 

cranialrectosis

Faster than a speeding faceplant!
Mentor
#14
Nice one Twitchity!

I'm trying to go a bit further down the rabbit hole on this build. I had the servo apart this morning so I could trim wires, sleeve them and replace the signal wire with one to match the color of the copter. For all I know, I just cooked the servo, but I'm gonna give it a shot.

I should get the Arduino wires and power rails for the ESCs all sleeved and the ESCs connected to the motors today. I put some pics in the third post.

Just waiting for the 1A Pololu to arrive.....

Oh and for as often as I hijack threads, feel free everyone to get your shot in now! :)
 
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cranialrectosis

Faster than a speeding faceplant!
Mentor
#17
I got my Pololu today. This copter is really coming together.

It's time to plug in the Naze to USB then I will grab the safety glasses and try a lipo. :)
 

makattack

Winter is coming
Moderator
Mentor
#18
I'm following this thread pretty closely. Just starting with multirotors myself, so I'm probably multiple years from what y'all are doing, but I love the Electrohub tri, and how it flies, so imagine a mini tri would be incredible -- even if it would be a handful for me.
 

cranialrectosis

Faster than a speeding faceplant!
Mentor
#19
I have been doing this since June of 2013. The reason for this thread is to show that you don't need to be a rocket scientist to build a copter and fly.

Once you can fly and flip your copter and if you are looking for a challenge, ring up Twitchity.

If I can do it, you can. :)

Besides, this is FliteTest. You don't build alone here.
 

cranialrectosis

Faster than a speeding faceplant!
Mentor
#20
Nothing exploded when I connected the lipo. The servo pushed hard to the right so I gotta figure out what that's about.

The Naze connected to Baseflight, flashed and I have it set up as a tricopter with my preferred PID and receiver settings. We're in the home stretch now!