RC Tanks Australia Forum

Building A Better Mousetrap - Taipan2014

Ok, thought I might do something different. Instead of posting about a tank build I thought how about posting about an electronics build? Then why not make it a build of a complete tank control unit? Probably boring to most but at least it will be different. So here goes.

First up if you are wanting to DIY control unit your going to need PCB design program, lots of time to research stuff on the internet and knowledge of how to program micrcontrollers. NONE of which I had 3 yeas ago. Except the internet time . I'm going to run through making up a Taipan2014 board and compare and contrast the design elements with other existing units.

Voltage Supply
The first thing any control unit is going to need is a power supply. Typically control units use at least 2 voltage supplies but more likely 3. These supplies are Battery voltage, 5V and sometimes 3.3V. The battery voltage is used to run the motors, 5V to run the controller circuitry in conjunction with the 3.3V which is used typically with sound cards/SD card interfaces.

Battery Voltage
Because of the 'Tamiya' legacy 7.2 V is somewhat the standard voltage used. However, tanks are getting heavier with all that extra metal and in my opinion 7.2 doesn't cut it anymore so this design/build is going to use a 3 cell LiPo 11.1V as the standard battery voltage. Not only will this extra voltage give the motors more power to drive metal tanks it will also provide the required voltage to drive external audio amp modules or 12 V camera systems. All of the current higher end boards from EL Mod, SGS, IBU and so on can handle 11.1 V supplies. The RX18 most certainly can not.

5V Supply:
The controller circuitry requires a stable 5V supply and for this low dropout voltage regulators are used. The El Mod ECO board uses a 5V TS2940 regulator which can supply 1 amp of current. Who knows what is on the Heng Long or Taigen boards since the Chinese love to scratch off any id numbers on the chips. However, there are no components on these boards to suggest that the 5V supply is anything more than 1 amp. Why so much concern over the 5V supply. Well it is because of the increasing trend to stick servos and other 5V gear into tanks. Again the more metal the heavier the part the more grunt required to move it. Since these servos run off the supply to the receiver there needs to be enough available current for both receiver and servos. To this end I suggest the use a 5V low dropout regulator that can deliver 3 amps of current. The downside is that such regs cost much more and take up more room. For Taipan2014 (as with Taipan V1) the LM1085IS-5.0 will be the 5V regulator of choice.

3.3V Supply:
Easy one – let the audio board take care of this.

Protection:
Always use protection boys & girls . For our power supply this means at least 2 things – reverse polarity protection and over current/short circuit protection. Reverse polarity protection will stop any damage from connecting your battery wires round the wrong way. Apart from clear labelling I can't see how the EL Mod Eco board deals with batteries connected the wrong way round and only polarity plugs protect the old RX18. Since T2014 (Taipan2014) will be using a simple terminal block for the battery connection reverse polarity protection is a must. For greatest efficiency this is done using a p-channel mosfet which will only turn on and supply current to the circuit if the polarity is correct.

For over current protection – good old fuses are used. Since there are 2 supply circuits (sort of) there needs to be 2 fuses to protect. The El Mod Eco uses a somewhat clunky inline fuse for the battery supply and a nice elegant SMD fuse on the board for the 5V supply. The SMD fuses look neat so T2014 will use 2. Again the SMD fuses are more cost and having 2 on the board will increase the board footprint.

Smooth and Chill filtered:
Well it would be nice if I was making some moonshine but alas... I'm talking about capacitors and such. Capacitors are important for maintain a constant/smooth voltage. If you think about voltage as being a road on which the microcontroller travels the smoother the road the better the performance. Capacitors are like trucks containing sand that can fill in any potholes in the road to ensure a smooth ride for the microcontroller. In general the bigger the capacitor the more sand to fill potholes. Similarly, the closer to the controller the quicker the capacitor can fill the holes. So if you want to make sure all holes can be filled you need to have a big truck to carry lots of sand. To this end Taipan2014 uses a 2200uF capacitor on the battery input and a 330uF tantalum capacitor on the 5V output. In contrast the El Mod Eco uses a 1000uF capacitor close to the motor outputs. Since the 2200uF cap is located on the battery input and away from the motor controllers the Taipan2014 design compensates by using includes 2 x 330uF additional capacitors adjacent to the motor controllers.

I suppose I should mention inductors at this point as inductors also help to maintain a constant supply of current to the system. At present the T2014 design does not include any inductors. If required they can be added in at a future point.

OK then lets get soldering.....



Now the test - connect a battery and lets see if the LED lights up...



Woo hoo - so far so good. I guess it is onto the next step - the Commander module

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Command & Control

If you are going to DIY your control unit then you will need to decide upon what microcontroller you are going to use. Coming from a non programming background I found Basic easiest to grasp and as such use Microchip PICs. However, with the rise and rise of Arduino ATMega processors may be more preferred. Really this is such a personal choice as you need to be comfortable with whatever controller you use. Since many RCTA boards already use PICs and have had years of development Taipan2014 will make use of this and possess a rather unique control process.

It was easy for me to think of controlling the tank exactly as a human crew would do. With a main controller (the Commander) controlling secondary micros, Radio operator, Gunner, and loader. This makes even more sense given that the existing GEKO essentially operates as a gunner controlling the gun position while MAKO is possibly the best loader in the game. All other tank control units appear to use only a single microcontroller for all functions. Whilst this is very neat and efficient the separate units on T2014 allow for much greater options and interface ability. Hence the current T2014 control map is:

Commander MCU – directs all other chips while taking care of driving and sending sound instructions to the separate sound board.

Radio Operator MCU – processes the signals from the radio receiver passing them onto the commander when requested

Gunner MCU – essentially a GEKO – controls the operation of the turret and gun elevation

Loader MCU – the famous MAKO – will allow for battle with the major tank brands plus provide a wide variety of IR shot types such as high explosive, armour piercing, machine gun, repair, or flak.

The downside of having all these separate controllers is that the can not be a single USB interface port for firmware updates. Consequently, T2014 still make use of the separate RCTA program cable for programming/updating the individual controllers via USB.

OK so once you have your Command and Control sorted it would be time to add the micros to you PCB. Since the main micro on T2014 is a 40 pin chip the next step is to solder this to the board and check that all is good before continuing.



Apparently all good - boy was it a pain to solder in that bugger. Next up the Radio Operator MCU

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Radio Operator MCU

I guess the next most important controller is the radio operator. Connection to the receiver in all other boards is via the main microcontroller unit (MCU). However, T2014 has a separate controller for this primarily because it requires an eight channel receiver for operation. This means that up to 5 pins on the main MCU can be freed up for other tasks. It also means that the main MCU is not 'bogged down' waiting for receiver signals. The radio operator MCU constantly monitors the receiver channel signals and passes them onto the main MCU when requested.

Once added to the board a test of communication with the receiver needs to be completed before continuing on. Taipan2014 has a lot of switching options so it makes sense to test tank ignition along with all of the lighting functions.



Since Brisneyland is shut down for the G20 I won't be getting some little parts for the MAKO circuit so over the weekend I'll be checking interaction with the sound board.

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Initial Sound Check

Once communication with the receiver has been established checking the connection to the sound module is a handy next step to provide audio prompts as to what is going on with Taipan2014. The sound module is a separate board that fits on top of T2014 and thus a simple male to female header connection is all that is needed.

The sound module I'll go into later but for now it is loaded up with 'prototype' sounds. Users can change sounds very easily and by using standard CD quality wav files there isn't any weird sample rate formats to deal with.



So the sound connection is working - there is a lot of work ahead in the sound area as T2014 will probably have more sounds (up to 250) than any other existing control unit.

Next up I'll get T2014 some IR firepower by adding in MAKO

Cheers
Kevin G

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MAKO MCU – Let's Get Some Firepower Pt.1

The MAKO program has been around for a few years now and contains so many features and options that I often get asked if MAKO itself is a complete control unit. Fusing MAKO into T2014 really is a no-brainer as it instantly adds the best Tank IR battle functionality available. The biggest change to the MAKO system on T2014 is a minor one but big in the overall picture. All previous MAKO have had the indicator LED triggered with a high signal. The circuit has changed ever so slightly so that now the indicator LEDs are triggered low (connection to V0). This change makes the MAKO and more importantly the connected Battle Unit electronically compatible with the Tamiya style mushroom. Hence any T2014 mushroom will work with the Tamiya MFU and vice versa.

All of the features of MAKO have been brought across to T2014 and there are the 3 x 3pin headers for connection of a recoil servo, Manta LCD and Remora wireless link. There are too many features for a single video and the next video will probably continue on with the MAKO features.



IMPORTANT – you may note T2014 does not feature and onboard DIP switches for the setting of weight class or other variables. All programming of T2014 is done via a SONY TV remote and the MAKO IR interface. Briefly pressing any of the numbers on the keypad during the program period will provide the following setup:

1 – light battle tank
2 – medium battle tank (default)
3 – heavy battle tank
4 – light bergepanzer
5 – medium bergepanzer
6 - heavy bergepazer
7 – MAUS (super heavy tank mode)
8 – medium Flakpanzer

9 – toggles between tank mode and halftrack mode (in halftrack mode CH1 is connected to a steering servo while CH2 provides the throttle to the twin motor controllers, there is no mixing of CH1 and CH2)

0 – Requests the Tank setting be displayed on the Manta LCD

Menu – enters Unit ID setup.

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MAKO MCU – Let's Get Some Firepower Pt.2

Geez a lot of things go on when you fire the cannon. Today was spent on just a simple action. Personally I love the recoil servo setup but many of you may have Tamiya/Taigen/Asiatam type recoil motor setups. Problem is those noisy, current sucking, EMI generating little motors. Sure enough some mods are going to be needed to deal with these motors a bit better. Once running they do cause interference with the receiver. A couple more caps and a fiddle with the programming and a day of trail and error and the recoil motor function is operational.

Also fitted today the connection for the Cannon flash. This is a 3 pin plug that can either be configured for a Xenon flash unit or a simple high intensity LED. From left to right the pinouts are: V0, V+, Signal V+. Use ali three for the Xenon flash and only thee outer two pins V0 and Signal V+ for a simple LED.



Those of you 'on the ball" will have noted that the motors run with the engine off. Big day today so think I'll just fix that issue tomorrow.

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Sound and Motion Pt.1

I guess most of Taipan2014 is sound and motion and from most of the feedback I get sound is a priority over motion. This is bit of a shame as I think the market would prefer product with loud booming sound and crappy motion over less volume and great motion. Fortunately T2014 aims to have both great sound and motion. To this end CH6 is dedicated to sound control. The middle band of CH6 is for volume control while the upper and lower limits trigger the 4 user sounds. Though I say 4 user sounds it is in fact more than 4. At present triggering one of the user sounds will actually select a random sound from a group of 5 making a total of 8 user sounds. As noted before there are a LOTS of options for T2014 which is why it is being developed in conjunction with tankER9X running on a 9XR Pro or with the Taranis radio. Simply, there are few other radios with the required amount of switches to run T2014.

Todays video demonstrates CH6 in operation controlling volume and triggering the user sounds. It also features the setup for a LED to be used for the cannon flash and the fix for the motors running while the engine is off. If you are on the ball you may note that the drive sounds for the main motors is not yet implemented. This is a big job and everything else need to be 100% before programming for this starts.



Next up I'll pop off the sound module for a look at the motor drivers....

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Under the Hood – Driving forces

Without getting too technical it's time for a look at what is under the hood of your tank controller. Typically the drive motors are controlled by Mosfets in a H- Bridge configuration which allows for speed control along with forward or reverse motion. These mosfets can exist as separate components or all integrated into a single IC. With the cheaper controllers the turret and elevation motors do not have such control. They may be operated by a simple on or off function as the case with the elevation motor or on/off/reverse/forward as with the turret motor. There is no speed control (proportional control) with these motors using the cheaper controllers.

Cheaper controllers tend to use separate and discrete MOSFETs in their design. The higher end controllers tend to use integrated Motor control ICs. HOWEVER, this is not to say that the integrated ICs are better. Taipan V1 featured a board with individual MOSFETS that was on par with the integrated ICs. What is important is the quality of the components, high quality mosfets = $$. Cheaper boards are cheaper because …. well you can do the math.



Here is a great page if you are interested in finding out more on H-Bridges
http://www.robotplatform.com/howto/L293 ... ver_1.html
As you can see it is written around the L293 chip used on Taipan and the El Mod Eco

Taipan2014 uses integrated motor controller ICs for both the drive motors and the turret and elevation motors. A L293 chip for the turret and elevation and 2 x VHN3SP30TR-E ICs also found on the EL Mod boards for the main motors.

Now I should point out here that the motor control options above relate specifically to brushed motors. Brushed motors are by far the most common motor used in tanks. In my opinion brushless motors which require slight different circuitry won't really get much traction until there is more support for them from the bigger manufacturers. Support for brushless motors will eventually be included on T2015B (Taipan2015 Brushless Edition) BUT users will need to get their own ESCs. Such a board will not then include the VHN3SP30TR-E ICs and hence will be cheaper to produce.

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Drive Motor Function & Battle Damage

One of the main reasons behind T2014 is the desire for more realistic battle scenarios. I have never been a fan of the massive 50% decrease in speed after a single hit. This usually ends in tanks all huddled together in some sort of mating battle ball. More realistic would be graduated levels of damage and that is what T2014 will be programmed for by default. With each hit, speed is decreased a little each time.

Not only will battle damage affect the main motors but it will also affect turret rotation and more than likely other scenarios as seen in WOT such as blown off tracks, increased loading time or ammunition supplies being destroyed (decreased magazine). These other damage options will be added in once all the basics are good.

The video below show how motor speed is affected by increasing battle damage. It is a mere substitution of values in the program to change this style to emulate that of the Tamiya system.



Don't know what will be the video for tomorrow....

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Lets Get Movin'

Well I guess you are all bored with the test bench videos – I know I am. Time to put T2014 into a tank and have a drive. Bit by bit of course. So this video sees T2014 in an old Matorro King Tiger. I have taken off the top hull so that you can actually see it is the Taipan board in there.

The last few days have actually been spent on the turret rotation sounds. At present there are 6 different turret speed sounds along with start and stop sounds, making 8 in total. However there are also turret variations such as manual turret rotation and damaged turret sounds. So at present about 20 sound spots are allocated for the turret.

Only basic sound work for the main motors – I have left the motors and sound to last so that I know how much program space to allocate. At present there are only idle, low speed and high speed sounds. I'll probably slowly add to these sounds as I tweak some of the drive algorithms/equations.

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