HobbyKing.com New Products Flash Sale
Thread Tools
Old Apr 12, 2013, 03:16 AM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
Build Log
1/5 scale FPV sentry rover

Hi there,

for unspecified reason some time ago I decided to build a kind of sentry rover.

The requirements were:
platform big enough to hold all the electronics and pan/tilt system
pan/tilt system to hold and able to move at least 6lbs weight
fpv gear for out of sight control
all terrain capability
rover capable of very slow movement
get it all made with limited funds (~1500$)

Possible additional features:
weather proof gear
alternative control method
waypoint navigation with obstacle avoidance

After a lot of searching I decided for RC4WD's Killer Krawler 1/5 scale version, as a rover platform.

I shall try to document all the steps of the build in this thread.
icah is offline Find More Posts by icah
Reply With Quote
Sign up now
to remove ads between posts
Old Apr 12, 2013, 03:36 AM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
The rover platform (kit):

RC4WD's Killer Krawler is a crawler kit which comes without any electronics, wheels, cables, simply nada.
Just the bare chassis with axles, gearboxes and 2 pinion gears.
My decision was mainly influenced by the fact that it is of 1/5 scale and all the parts are crafted (CNC'd) from aluminium, no plastic parts.
All the parts fit nearly perfectly so the manufactoring process quality is high.

The main features:

CNC Machined Killer chassis
CNC Machined Killer axle
Heat treated stainless steel spool gear
Max volume adjustable piggy back shocks
Killer angled suspension arms
Front and rear billet bumper
Full metal steering kit
Full ball bearings
1/4 scale servo mounts
Gear ratio: 30:1
Length: 546mm/21.5 inch, Width: 510mm/20.47inch, Height: 250mm/9.84inch, Axle ground clearance: 70mm/2.75inch, Middle ground clearance: 150mm/5.90inch
Wheel base: 22.4" (570mm) wheels on-center
Includes standard 1/10 scale servo mounts

The kit is available from their site only, for 700$.

Killer Krawler 1/5 scale crawler kit build log (2 min 31 sec)

NOTE: this is a 2008 year model and already discontinued, so spare parts would not be get so easily,
on the other side, any part of the kit can be recreated If one has a good connection to a CNC expert.

Wheels, wheel hubs and tyres:

The KK kit comes with 23mm hex wheel hubs by default. The problem with this is that there are not so many
wheels which fit this size. Fortunately, RC4WD offers 24mm conversion hex hubs, around 30$.
By using these, I am able to use any wheel with 24mm hexes.
I searched primarily for HPI Baja 5 type wheels and finally ended with cheapo aftermarket Rovan wheels&tyres.
These are 195mmx80mm with offroad pattern and will hopefully offer anough drag. They cost me around 140$.


For the electronics, I wanted to buy some relatively cheapo but reliable parts, so I decided for HobbyKing.
(I know some says the reliability is not common with Hk parts but after 100+ orders I still have good experience with them)


The manufacturer suggests 540 sized brushed motors with the crawler.
Many of the guys use quality Novak brushed motors for crawling but they are too expensive for my application.
Plus, I did not want to do the regular maintanance of the brushed motors after a few runs.
Present year is 2013! So I went for brushless, of course.
As my rover has 2 axles I decided to use 4WD, instead of just 2WD, that means 2 motors, one for each axle.
This allow more power for rough terrain.

As the final gear ratio comes to 1:166 with the factory 9P pinion gear I wanted a slow kv brushless motor
and because of the capability of slow speed it had to be sensored, to avoid any cogging.
I had to find a motor which is not bigger that a 540 size brushed one, so the upper links can move freely.
Although RC4WD offers 750 size motor mount I am not sure how can these fit not to block the upper link movement.
As my factory pinion gears are for 3.175mm shaft the motor has to have the same.

And the winner is the HK's Turnigy TrackStar 21.5T Sensored Brushless Motor 1855KV.
I was a bit afraid of the fact that its maximum power usage is only 150W but it seems to do the job well.

Killer Krawler 1/5 scale with brushless motors (3 min 56 sec)

NOTE: the motor cables are not interchangeable, they have strict positions to fit in the esc,
when using a sensor cable.

Speed controllers:

As the maximum drain of my motors is only 22A any 45A sensored ecs would be enough but for future
upgrade plans I went for 80A escs.
I chose the HK Turnigy Trackstar 80A Turbo Sensored Brushless 1/12th 1/10th ESCs. They only need to get calibrated
and are ready to go.
Many more features can be programmed but only by a specific card which is in BK all the time. So I am using the default values.


As my wheel diameter is 195mm and width is 80mm I bet I would need high torque servos.
Most of the guys use >20kg servos for this beast so I decided around this value.
Again, a cheapo solution from HK: BMS-L530DMG Digital Servo (MG) 19.8kg / .15sec / 140.5g
Plus, I have ordered some heavy duty alloy servo arms.
Unfortunately, the HK Post is unable to deliver the servos for more than 3 weeks so I could not test them yet.

RC system:

I am using the T9X with Frsky telemetry capable module, with factory firmware.
icah is offline Find More Posts by icah
Last edited by icah; Apr 13, 2013 at 04:16 AM.
Reply With Quote
Old Apr 12, 2013, 04:45 AM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
This is where the project recently is.

The steering servos are on the way, the pan/tilt system with the servos is on the way, the GPS is on the way
and now I am thinking of an APM 2.x module for waypoint navigation to buy.
I would need to buy the video transmitter for FPV so I do not have to relocate the existing from my quadcopter.

However, in the meantime there came an idea about alternative RC control so I went for it.

Arduino based RC control with speech recognition module:

The main idea is quite simple: get a speech recognition module, bind it to a microcontroller and send the output PPM signal to a HF module.
Get the servos move on the other side, 1km far away.

Most similar projects use the speech module to drive a car locally, i.e. in the range of its microphone.
When you are more than few metres from the car it is useless.
For FPV purpose, the signal generated by the speech commands need to get to the receiver, far far away.

The hardware chosen:
Veear EasyVR module (shield) with mic
Arduino Uno
8 ohm 3W speaker

The SR modul cost me ~60$ and the Arduino board ~20$.

For the code I borrowed the RCLibrary for arduino, written by dvdouden and a piece of script I found in the net for light control by easyvr module.
By creating a symbiosys between them it seems that this idea comes to life.

For testing the PPM output, I have made a simple mono audio cable.
One side of it goes to the PC microphone, and the center of the other side to the arduino digital output pin where the PPM signal comes out.
The PPM output and channel behaviour is tested by the PPM Audio program.

There is still so much to tune in the code but the result with this version can be seen here:

Speech recognition RC transmitter module (2 min 37 sec)

For the HF part, I have ordered this modul from HK: FrSky DHT 8ch DIY Telemetry Compatible Transmitter Module.
Unfortunately, it is still on the way...
icah is offline Find More Posts by icah
Last edited by icah; Apr 13, 2013 at 04:18 AM.
Reply With Quote
Old Apr 16, 2013, 01:41 PM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
I made some progress during the weekend.

As my 20kg/cm servos are still on the way I decided to throw in some 4.7kg/cm servos for initial tests and went hill climbing.
I was a bit afraid as the rover is quite heavy, about 15lbs, and there is just the basic electronics built yet, so It will get heavier soon.

The result is here:

Killer Krawler on steep (3 min 11 sec)

The motors are surprisingly strong enough for climbing on rough terrain. The servos lack power but are comfortably usable for the ride.
Nothing is warming up, neither motors, nor servos or escs during a 10 minutes ride.
I have charged back ~1Ah into my 5Ah LiPo after the full ride.

The only problem is that I do not have a programming card to this specific esc (always backordered @HK).
Thus, I am not able to set the brake power correctly.
This way sometimes happens that if there is not enough time left after a brake for forward or reverse drive I get only 2WD.
However, after the braking when I wait ~1-1.5 sec then all the wheels are powered again.

Another thing is, when I do a sudden brake while driving forward the back wheels stop immediately while the front ones slow down gently.
The same is true for the opposite direction. This is because of the mix on the radio and can be corrected by programming the brake on both escs.

However, the vehicle will not function as a crawler so it does not matter much If I have only 2WD for a few seconds. But it is annoying a bit.

And here is the first test of stair climbing:

Killer Krawler first climb (1 min 21 sec)

In the meantime the pan/tilt unit arrived from Robotshop so maybe tomorrow it will be the next to assembly and test.
Ohh, I did not mention that the rover will be equipped with a pan/tilt unit that will serve as a kinda turret holder , did I?
For first tests it will host a well-known type airsoft handgun. Later on the same platform will host something different...
icah is offline Find More Posts by icah
Reply With Quote
Old Apr 21, 2013, 09:07 AM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
The pan/tilt head from Robotshop finally arrived, as well as my 20kg/cm Bluebird servos.
So I exchanged the former Hitec servos for the Bluebirds. They are a bit noisy as they are digital, but they do nice job.

The tilt mechanics has been fixed to the pan base. The FOV is ~120 degrees which is comfortable for FPV riding and turret aiming.
The movement of pan/tilt is fast enough for future aiming.
An 1lbs airsoft handgun has been fixed on it and tested the movement. So far so good.
Unfortunately the mechanical structure of the gun does not allow to pull the trigger with any kinda servo, while it is too stiff.
I need to find some other turret solution.

For now, here is a short video and some pictures:

Killer Krawler transforming to rover (3 min 53 sec)

For easiness of control, I am using the right potmeter on my radio (AIL,ELE) for riding and the left potmeter (THR, RUD) for the pan/tilt head control.
icah is offline Find More Posts by icah
Reply With Quote
Old May 03, 2013, 08:31 AM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
There is a new progress with the speech recognition module.

The DHT HF module has arrived some time ago and now it is connected to the
Arduino board and EasyVR module.
For some time I was fighting with the connection of Arduino output signal to the HF module.
With the help of some guys from the local RC forum now it is working well.
By modifying some existing codes now I am able to generate clean PPM signal via Arduino board and send it out to the HF module.

Everything works as expected (no servo jitter and such), until I start using the EasyVR module.
For some reason (most possibly waiting for some slow interrupts) the servo connected to my receiver jitters, sometimes quite badly.
I am trying to find a solution for this but there is also a plan B to use 2 Arduino boards, one for generating the PPM signal and one for speech recognition.
That way there should not be any interrupt problem, thus, any servo jitter.

For now there is a short video about the progress:
EasyVR + PPM generator (1 min 56 sec)

For any case, I am ordering another Arduino board and hope it will arrive within one week so I can continue with the project.

In the meantime, I found a solution for the airsoft turret. Soon I will describe it here.
icah is offline Find More Posts by icah
Reply With Quote
Old May 04, 2013, 10:03 AM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
Finally I found a solution for the servo jitter problem today. As suspected, the SoftwareSerial library of Arduino was interfering with the EasyVR library.
After reconfiguring the software to use hardware serial now it is working as expected.

So what we have here is currently 4 channels (can be raised up to 13) that can be controlled by speech.
The test below confirms the concept (with 2 channels). For english language commands wind to 01:15:

Speech based RC control finalized (2 min 11 sec)

Within the next few days I shall build this solution to the rover and find out how to make the control smooth. Stay tuned
icah is offline Find More Posts by icah
Reply With Quote
Old May 06, 2013, 10:47 AM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
I have written the code for the mixing of throttle and turn channels during the weekend and tested it yesterday.
The whole solution has been tested in the rover.

Control is quite responsive, now the only issue seems to be the microphone sensitivity to nearby noises.
Unfortunately, what is 100% in a quiet room that is not as good in the open area.

Check the vid:

Rover speech controlled (3 min 2 sec)

Soon I will try to change the stock mic into some noise canceling one.
Hopefully that will improve the recognition up to 100%.
Apart from this minor technical issue I am satisfied with the result.

Soon I shall build in some more words for controlling smoothness of throttle and steering.

Then the next step is to mount the fpv gear and go outside and test everything working at distances of more hundreds of meters.
icah is offline Find More Posts by icah
Reply With Quote
Old May 27, 2013, 01:09 AM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
Some more progress has been made.
The stock microphone has been exchanged for a noise cancelling one.
Speech recognition rate is now close to 100%.

More commands are going to be implemented into the code, for speed adjusting and turret control.
I am thinking of building a kinda pointer for the turret (as both my hands are free during RC control),
something similar to the Wii Nunchuk but in a manner of point and shoot. Seeking for technical solutions.

Check here:
Killer Krawler speech control in field (4 min 41 sec)

In the meantime the airsoft weapon for the turret has arrived.
I decided for a Well D93 because it can be bought and delivered to EU quite cheap.
The bullet feed mechanism is gravity based only and is not the best I have ever seen but it hopefully does the job.
The mini uzi will be dismantled and rebuilt as a turret soon.
icah is offline Find More Posts by icah
Reply With Quote
Old Jul 21, 2013, 12:43 PM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
Finally found time for finishing the project (first draft, at least).

The gun:

Feed and capacity:

The Well D93 has been modified a bit and positioned upside down. The chamber for the BB bullets has been reversed as well.
For now, a simple tube has been added for feeding the chamber. The capacity of the tube is ~30 BBs.

Power supply:

First I tried to power the gun with 6V from a DC-DC converter but the fire rate was as high that it caused malfunction while feeding, so I decided for 5V.
By using this voltage, feeding is correct and the fire rate is still affordable.
The only problem was that the cheapo chinese DC converter provided insufficient current for the gun so it could not work.
I had to order another one, with 5A throughput current. It was delivered a few days ago and built onto the vehicle.


The trigger has been taken out and replaced by an RC channel controlled electronics. It triggers when the channel PWM rate is over 50%.
The Arduino code has been modified accordingly. Fire duration has been set to 500ms.

The fpv gear:

For now, the vehicle got my old 200mW 5.8G trasmitter with a very light and small 520TVL 5V camera. Only bench test has been made so far.
Video shot in the field will follow soon.

As the tilt servo holds the full weight of the gun platform it can be easily damaged while rasing in the field.
The weapon will be initially set into a parking position and raised only when armed.
For this, some modification in the Arduino code is needed.
The fpv range may be insufficient, first field tests will show ho much. Consider using a 900MHZ gear.

The bench test of functions:
(warning, commands and description in Hungarian language only - yet)

Killer Krawler armed - bench test (2 min 37 sec)
icah is offline Find More Posts by icah
Reply With Quote
Old Nov 15, 2013, 03:50 AM
Registered User
Joined Nov 2013
1 Posts
Hey Icah,

Great project, thanks for sharing your efforts.

I love the killer krawler chassis, beautifully made and very capable. I am working on a similar project - rover, apm2.6 controller platform, 3dr radios for control and telemetry. For groundstation control I have a web based app and using a flight stick for input.

I would have loved to have gone the krawler route but very expensive. I opted for the dagu thumper 6wd, not quite so cool, but also capable and spa e for component placement. You must find space quite tight in the krawler?

I have yet to install an airsoft - i would dearly love to have it custom made so as not to look like a hacked toy gun, yet that will cost, or I design a 3d printed case for it.

How are those bluebird servos holding up to supporting the gun?

Great work.
Grumpybeard is offline Find More Posts by Grumpybeard
Reply With Quote
Old Nov 18, 2013, 11:41 AM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts

There are no issues with the servos, they hold the ~1kg rock steady.
However, the pan/tilt mechanism feels a bit weak and I am afraid that at full speed on bumpy terrain it may break.
A stronger one would suit better.

The available space is quite tight but sufficient for the electronics.
I know I could made a better deck for the gun and electronics but I was in hurry to try it out finally.

Yes I have chosen crawler chassis to eliminate any limits of different terrains.
Initially I bought it for using it with Ardurover code but then I got that weird idea of speak control so I gave up with APM for now.
But may get stuck into it again later. The chassis will nor corrode or dissolve so I give it a time
icah is offline Find More Posts by icah
Reply With Quote
Old Feb 04, 2014, 04:56 PM
KF5LDN FPV Junkie!!!
Wizzard033's Avatar
United States, TX, Lubbock
Joined Nov 2009
1,758 Posts
How is your project going?
Wizzard033 is offline Find More Posts by Wizzard033
Reply With Quote
Old Feb 05, 2014, 01:49 AM
Registered User
Hungary, Pest County, Tököl
Joined Oct 2010
356 Posts
It is frozen a bit due to another projects.
The last thing I made was to put all the TX electronics into 1 box so I could use it in a carry and go way.
This way I only put on the headphones, power on the box and play.

The vehicle is getting its rest until spring, at least.
icah is offline Find More Posts by icah
Reply With Quote

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Sold Ikon N'wst 1/5 scale Super Cub joedoan Aircraft - Fuel - Airplanes (FS/W) 1 Apr 09, 2013 07:51 PM
Sold Ikon N'wst 1/5 scale Stinson Reliant SR8 joedoan Aircraft - Fuel - Airplanes (FS/W) 2 Apr 08, 2013 09:37 AM
Sold HPI Racing 1/5 Scale Super 5SC Flux 4wd Truck RTR JHawk19 Cars - Trucks and Parts (FS/W) 4 Apr 06, 2013 04:28 PM
For Sale 1/10 Scale new bright land rover body HyperHelis Cars - Trucks and Parts (FS/W) 4 Jul 12, 2010 01:50 AM
Sold 1/10 scale Rover Body lv2soar Cars - Cars and Parts (FS/W) 0 Jul 21, 2009 11:29 PM