Killer Krawler 2 Build Log (end 2018 project)

[stonely0]

I am a RC fan, from on road to off road and crawler, from heli to glider to tri / quadcopter. Occasionally I dabble in robotics and building a rover with robotic arms had always been part of my wet dreams. In the past, i had dabble in Arduino programming and manage to build a few small robotic projects but the progress are some what slow and controlling with codes are nothing as lively as traditional RCing. However, these project had expand my knowledge beyond conventional RC building. Eventually, I had put aside the robotic rover project due to the facts that there are no decent chassis available online that is huge enough to be customised and still look super cool. Servo City and Spark Fun offer a few chassis and they are not only expensive but they looks like high school STEM projects and missing the 'Cool' factors and the build always looks very raw and ‘Boxy’. Recently after looking through some You Tube video I came across a chassis that is exactly what I had in mind for a long time. It’s the RC4WD Killer Krawler 2 (as Killer Krawler 1 is discontinued). Information for this chassis is scarce… almost nothing came out that can be useful for my build research. Luckily, someone is crazy enough to have a build video in his channel and that had become my only source of reference. Sadly, all the question I wanted to ask the builder came un-answered! Maybe he is a busy man or maybe answering comments is just not his cup of tea.

After like about 4 months of coming to a road block on research and realizing that this Chassis is going to be discontinued soon by RC4WD judging by the virtually no spare for this chassis on their webstore and it doesn’t help when some parts meant for this chassis are already discontinued like the wheels and motor… I decided that if I really want this chassis it will be a shelf queen! So, I scrap the idea of building one. But Black Friday sale came to RC4WD and the offer is too good to be missed, so when on a business trip in Korea after consuming a full 750ml of Korean rice wine I reach my hotel room tipsy and spread out on bed checking my email… “Bing!”, the email came from RC4WD for the start of Black Friday sale, a quick check, everything was at a discount too good to missed! I sprung out of my hotel bed and make some quick purchase while trying to not make any mistake from the effects of alcohol toxication. Done checking out my cart and collapse into the bed knocking out!

Next day, I woke up, a snow storm outside my hotel in Seoul and an afternoon flight to catch to Tokyo for my next leg of business trip in the evening before heading back 1 weeks time to the warmth of Singapore. So, with enough time to kill, I began sourcing online for the electronic components like the Servo, ESC and stuff… My reference is still from the video of the man who did not revert to my comments. I ordered the same servo as his but not the same ESC as it will be an overkill for this build in my opinion. (But very soon in the later part of this log, I am puzzle how he get his servo to work efficiently…)

2 weeks later, all the item came to my home in Singapore. Yes, you know where I am if you catch the movie ‘Crazy Rich Asian’. True enough, the boxes are huge. Shout out to RC4WD for doing a good job on the invoicing that save me some money on taxes. (owe you folks a beer for this if u happen to be in Singapore please ping me!) I am taking my time for this build and so 1 week after its arrival, I unboxed it. I am not good in video otherwise I will post an ‘Unboxing’ video in you tube, I appreciate people who done that, just that it will be even better if they can take the time in answering viewer’s question. English is my 2nd language so, maybe my question is in-comprehensive. Pardon me if you get a headache really this post

Below is a few pics I am sharing now… more will come as I began my Xmas holiday tomorrow and focus on finishing this build that is nothing like a smooth journey! Stay tune!

The Boxes

(Shout out to RC Mart too for always helping me save some money on taxes)

I was abit skeptical when i see the 'Make In China' stamp om the box. I was expecting this to be a made in US of A item because of its price. But anyway, what are not made in China these days. Upon opening the box, i was pretty impressed by the quality. Although the instruction and and screw bags could be more easier if they are related. Example, the instruction call for the hardware in 'Bag 2' but there are no Bag 1, 2 or 3... just the name and measurement of the hardware. Overall, i am pretty impressed by this products but for this price, i am expecting more. Seriously.

OMG! I just love them shiny!

As seen here parts are laid in cut out foams. Impressive! one of the best kit presentation i had ever seen!

My choice of electronics are as followed: some are already in my stash and some i had to buy just for this build... talking about electronics, RC4WD have nothing in their store that are meant for this chassis... the original ESC for this chassis are discontinued! The servo that is recommended for this chassis for this chassis are forever out of stock! So are the motor... i got the last 4 and now it i out of stock until God knows when! there are virtually no hardware spares for this chassis at all in their store... this very much prompted me to believe that this chassis had reach its end of life and buying it now will be a shelf queen. So the choice is up to you... (or me i guess.)

for the Servo, i am at a lost as this is my first time building a 1/4 scale and my research shows that a 1/5 scale servo will not fit into the servo mount of this chassis. So i will have to go with a standard servo size which are most common for 1/10 and 1/8 scale. My choice are from someone who had already build it in You Tube video but not answering any comments i asked... that is the Savox SW1210SG - Waterproof High Voltage Digital Servo (Shown below)

These servo doesn't come cheap! When i was checking out these servo, a total of 6, i was like... "These better works!"...

For the ESC i go with this. Someone is using a Tekin RX8 which to me is an overkill. I go with the above which is waterproof and a Dual motor support and most of all, not over price for a brush motor which i am using.

For TX i used my existing stick radio from my Drone fleet...

For RX i will use the Frysky X8R. My intention was that 1 RX will be enough but as i found out during the build that i am suffering from serious power drain and i had to use 2 RX so that the 1 only focus on the 4 power hungey steering servo and the other will do the work for ESC and Diff lock servo

My choice of BEC will be the CC BEC 2.0

More update coming as i am building it and solving problem on this build... stay tune...

 

[Zukiiholic]

Welcome aboard.


How to post pics.
http://www.rccrawler.com/forum/comments-suggestions-help/28164-posting-pics-dummies.html

 

[stonely0]

Now, The kit came with some parts pre-assembled and what are left are only a couple of hours of work to have the chassis up. Although the instruction manual call for the pre assembled parts to be lock tight, i realised that some of them are already pre factory lock tight so to me i just leave them as it is especially the axle part. The package came with a small bottle of shock oil, a diff grease and a small tube of blue lock tight. I use the diff grease for the diff gears when i have to open them to install the motor pinion. The Instruction manual are generic and may not represent the parts you received. There are also some missing hardware although most of the hardware came with 1 extra spare (Hardware = screws and nuts) In this section i will only highlight area that required special attention when assembling the kit...

The diff case are tighten by 6 screws and have to be open when you need to install the motor and its pinion gear. The diff gears came factory greased but it is still best to grease it again with your preferred type of grease. For the pinion gear mesh, i use 2 small piece of paper to set the gear mesh.

The first major confusion is the wheel hub. The instruction manual is different from the parts that i received. below is the hub that came with my order vs the one shown on instruction manual above. RC4WD support says there will be no difference in installing the wheel even if my hub is different. Just screw it on they said!

I have a missing spacer that are suppose to be use here. Lucky for me i have some other same length brass spacer in my stash to solve this... So for my build, one side are brass color spacer! cool!

Next, i find it strange that RC4WD did not mention on the specific length for the servo arm used here to in the Diff lock mechanism. Standard servo arm will not fit as they are too long. RC4WD did have a shorter servo arm in their web store fit to do this but there are no mention of this in anywhere. Further more the shorter servo arm that RC4WD have is always out of stock!!!

Up next, The M4x32mm screw that hold 2 steering rod together will never be tighten even if you lock tight it. (Blue Lock Tight and i have no intention for Red lock tight on surface vehicle unlike aircraft or drone) I figure the best way is to change it to a longer screw and fasten a lock nut at the end will be a better option.

Finally, The M3x12 nut screw is something that most of us will not have the right tool to screw it in! I replace it with a M3 bolt head screw and it work just fine.

That is so far for now... more are coming...

 

[stonely0]

All about Servos...
In this section i will like to talk all about dual servo steering. Unlike Traxxas Summit, Which have 2 servo on the side, Killer Krawler 2 have two servo side by side(See below picture). In some build video i watch, Someone manage to use a 'Y' servo cable and linking them together into one channel. Unfortunately i realised, by doing that you will be having constant binding and no way to adjust each servo individually to stop the bind. It will end up with overheat issue and eventually dies.

Important: The servos are mounted on pre-cut holes on the chassis and it fits a standard size servo. That rules out the option for large scale or 1/5 scale servo.

This chassis have a total of 4 steering servos for front and back and 2 Diff lock servos. A total of 6 channel just for the servos alone and not using 'Y' cable (see above problem if you attempt to use a 'Y' cable) plus ESC and a Pan and Tilt FPV system (require 2 servo / channel) equals to 9 channel. I am using the Frsky X8R (8 channel) digitally linking to another X8R (8 channel) that gives me a total of 16 Channel for future expansion of LEDs or what not. However, going to this route i will need a dual pack lipos which for this chassis, is not a problem for top deck customisation on rooms for batteries. Power drain might be an issue that needs to be fix when it comes to electronics later. (i will include a section on this later)


Tricks to stop binding for dual steering servos
Its a bit tricky setting up dual steering servo that are laid out side by side and there are no instruction on this at all in the user manual. So its all about trial and error.

If you attempt to center both servo by eyeballing them and thinking that you can get away with it by adjusting it when you are done with the build, you will be disappointed and have to dismantle them all out again.

If you think you can get away with using a 'Y' cable and linking 2 servos into one channel you will be disappointed too as you will soon realised that it don't work this way.

The correct way is to use one channel for each servos....
1) Plug the servos into the receiver and power up the transmitter. Center each servo horn by using the sub trim function.

2) Assemble the steering bridge to the 2 servo horn. Listen for binding sound, usually when there is a bind the servo will give out a whining sound. If there is a bind, adjust each servo's sub trim until the bind stop

3) Hold 2 servo side by side using your hand tightly while the other hand steer both servo left and right. It is not easy and you need a fairly strong grip for these high torque servos. Steer left and hold it there. listen for any binding sound. If there are, adjust each servos' left EPA until the binding stop.

4) do the above for the right steer and listen for any binding sound. usually there will be and adjust EPA until the bind stops


Why do i have to do the above? Wont the EPA be the same?
If you follow the above steps you will soon realised that both servos EPA are different in order for them to not bind. If they are the same EPA you will be binding them until they are toast! The reason why the EPA are different are basically the 'Angle of Deflection'.

Unlike Traxxas Summit, Killer Krawler 2 have both steering servo side by side. so if you have the same EPA for both and when you try to steer either side one of the servo will bind as the steering bridge connecting both servo will move without much thought for the servo EPA. To compensate the angle of either side when steering left and right, one of the servo EPA will have to be lower or higher than the other so that when the steering bridge move horizontally both will come to a same position.

Its complicate but if you ponder deep enough you will understand why.

So it is important that when you reach the part for servo steering installation, take the time to solve this issue before proceeding because you will have visual on the servo before they are mounted on the chassis.

That is all for today. I will update more as i goes along...

 

[OSRC]

Very cool, don't think I've seen a build thread on one of these. Carry on good sir!

 

[stonely0]

Assembly...
The kit is a joy to assemble. CNC machining parts fits in place perfectly. Nothing major happened and i was able to complete the build in a day.

The cantilever shocks with upper link

The motor is mounted to the axle and the skid plate assembled

The wheels are gigantic. They are not loctite from factory so you will need to loctite them. The easiest way was to install the tire to the wheel, tighten all screws and than when you are satisfied with the tire sitting, remove one screw at a time, applied loctite and tighten them back in before proceeding to the next screw.

Turret Design...
After the installation of the tire to the wheel, i feel a need to take a break. Honestly, size 4.0 wheels required some brute force to get the tire in. The next day i spend the time going through my stash. I retrieved a mobius action cam from one of my hex copter. It have the docking station for Video transmitter.

mobius action cam with FPV transmitter dock

Next i go through my stash of structure component for prototyping build, i sat down for a couple of hours designing the turret to fit my Pan and Tilt brackets... the below is the result i had finalised. Blue is the only colour i have now and it matches the Savox waterproof servos... One day i will get this piece to the workshop and get it make from aluminium plate without holes.

This bracket will go over the skinny pan and tilt bracket i had from a couple of years back. It will balance out the build dimension from top to chassis. I will post a complete over all pics when they are ready.

Next post will be on the electronics and first bench test run...

 

[stonely0]

Electronics - 1st Try
I first started out with a 3s Lipo going through the CC BEC 2.0 to the Frsky X8R 8 Channel Receiver (in the sbus aux port, this way i get to save 2 channel), The Quicrun ESC without positive cable is connected to the receiver in Channel 1 and the rest of the 6 servo from channel 2 to 7. The BEC was set to 7.4v powering all servo and ESC via the RX. Frysky RX is able to handle up to 11v (if i remember correctly)

The sheer size of this crawler with the top battery deck and body post not assemble yet. This is how it first look like before i modified the top deck to hold 3 x 3s Lipos (Read further down as to why i have to go to this route)...

Bench test without load everything works fine. However once on the ground, and accelerating, i suffer from serious power drain. The RX starts to shut down whenever i try to turn and the crawler. I do not have enough to turn the wheel and drive at the same time.


Electronic - 2nd Try
Back to the bench, and after hours of trying to figure a best efficient way to handle the power drain, i realised that i have no choice but to add a 2nd RX + a 2nd BEC to power 3 servo from the back and 3 servo + ESC from the front.

Ground test, my servo now works with more power especially the rear 3 servos which are standalone with BEC. However, my front 3 servos with BEC and ESC to one RX are still lagging and not turning fast enough when i accelerate. Its an improvement from the 1st attempt but still not ideal to me.


Electronic - 3rd Try
This time round, i had decided to make the ESC stand alone with it's own 3s Lipo packs. That means that in total i am running the crawler using 3 x 3s Lipos. 1 for the front servos, 1 for the real servos and 1 for the ESC.

Internal layout of electronics deep in the bottom deck of the chassis. Seen above with 2 x RX (a total of 16 channel), 2 x CC BEC 2.0 (for the servos alone and 1 x ESC (with stand alone power source not sharing with the servos

Ground test is very positive. But now i have to think of how to mount 3 x 3s Lipo on board. I fashion the top structure with battery holder to hold 3 x 3s lipos in Left, Right and tail manner. All i did was change the body post assembly abit and fashion the batter deck with standoff.

I had assembled the body post not according to the instruction. I am using them as battery tray for left and right. I also fashion a battery tray using my prototyping structure to hold the 3rd Lipos in the centre rear of the chassis.

Over all Looks okay to me.

 

[stonely0]

Final Presentation
Below are some pics of the final presentation. at time of publish, i had since change some top deck attachment but over all this is how it will look for now until i get some more better structure components from Servo City.

Overall, i am very satisfied with the build. From building this myself, i had come to realised that not all online build video are accurate. Most time, there are bits and pieces of info that the user had failed to mention. I understand that it is never an easy task to build and video them for the audience all at once. for this, i appreciate what i can get from the handful of people who take the effort to have this information or video online as resources. i wish that what i have here can further help would be builder of this chassis in future...

Side view of the completed build with turret mounted

Rear view. With top deck, batteries bay, Infra red camera, multiple camera mount and Pan Tilt FPV turret camera

Front view with LED side head light (mounting fastener had been replaced with CNC machined knob not shown here), multiple angle fix camera mount on top and under deck, FIx IR camera, pan tile turret with FPV camera