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Tank Blog

An Accountant’s Guide to the Scorpion MK3 Mini Tank
(in chronological order)
By Paul Newbury


Thirty years ago, I attended a wedding in California where I rode in a tank that fired tennis balls. Ever since, I have wanted a tank. Today, I’m a retired accountant and I’ve finally purchased a Scorpion Mini Tank and this is my blog about purchasing and modifying it.

This is the 1990 tank I saw in California


When I set out to find a tank, the first thing I noticed was that lots of people were building there own tracked vehicles. As this was beyond my expertise, I searched the internet for off the shelf tanks. A used military surplus tank runs about $250,000. A Mud Trax starts at $40,000. The Rampage is really cool but only made for the military. The Chinese Fighter Tracks was priced under $10,000 but hard to import.

Research Notes 8/2019:
Argo information: Frontier 600 6×6 $10,000
Skid plate $310; Tracks $1,870 Plastic to $4,368 Rubber; ROPS $1,869

Lite Trax MTX-R  (Mud Trax)
Utah Manufacturer says they start at $36,000
Ken at 704-279-5736 in NC says $38,900 plus freight from Utah

Paintball Battle Tanks  (British manufacturer of Scorpion MK3) 0044 (0)208 4326423

The Combat Zone  (Georgia park with Scorpion tanks)
108 Godley Rd Bloomingdale Ga 31302 912-675-9952

OSG Paintball (NH paintball park with Scorpion tanks)
David Preston  1 800-707-7529
1053 N Barnstead Rd, Center Barnstead, NH 03225

Fighter Trax
The max speed is 7km per hour. We have no US distributor yet.   hdtk-200 do not produced any more, you can see if you are interested with DXTK-180. The price of DXTK-180, the FOB China port price is USD5200, to door freight is about USD1200. You can find how is the tariff from local custom clearance agency after Trump increase the tariff of goods from China. Any further questions, let me know. Pearl Zhao  

Fighters All-terrain Vehicle Technology Co., Ltd
Cell/We Chat/Whatsapp: +8615350592434

Scorpion MK3

I finally found a British tank manufactured by Paintball Battle Tanks. It’s a single person steel chassis tank with a fiberglass body and a very clever easy glide turret system. It opens like a clamshell and drives like a zero turn mower. It’s a true tracked vehicle with independent tank suspension with steel belt rubber coated tracks. It’s powered by a 500cc  Briggs and Stratton engine. It has a max speed of 8mph and weighs about 1100 lbs. It’s 6.8’ long and 3.74’ wide. The US distributor is Armourtrax and it sells for about $13,000 plus shipping and tariffs.

Scorpion Notes: 8/2019
I found Susan at Armour Trax through the Paintball Battle Tanks website which has a very responsive chat. Susan told me they expected their first shipment soon. She said there was a paintball park in Georgia and one in New Hampshire that had purchased tanks. Susan expects to take a tank to a trade show in Tennessee in February (2020). Susan said she would send me her standard letter.

Here is my standard letter:
My name is Susan, my husband Anthony and I just became the US distributor for Paintball Battletanks in December (2018).  Our company is Armour Trax and we are based out of WI (south of Hudson).  Our role for this company is to help facilitate sales and inquiries in the US.   The tanks take approximately 3-4 months to build and ship to the US. Pricing is as follows: 1 – 2 tanks: $13,000 each; 3 – 9 tanks: $12,500 each; 10+: $12,000 each . The manufacturer requires a 70% deposit (to begin the order process) and then the remaining balance, prior to shipping. Shipping costs vary, depending on how many ship per container and then US shipment on top of that.  I have a contact with a shipping company, who can give ball park estimates ahead of time and precise costs 2 weeks prior to shipment.  We estimate shipping for 10 units to cost somewhere around $3,000 – $4,000 total.
Please let me know if you have more questions.  
Thank you so much for your interest!
Susan, Owner, Armour Trax
**If you’d like me to price out the laser tag module, please advise and I’ll have David and Keith work something up for you.

OSG Paintball

Armour Trax, unfortunately had no stock so I contacted the paintball parks that Susan had said already had Scorpion tanks. OSG paintball is the largest paintball field in New England with 11 venues on 43 acres. David was very helpful and offered to sell me a used Scorpion Mk3 with only 8 hours on it. Nancy and I hitched up the trailer to the farm truck and headed to NH taking the 12 hour northern route through the Green Mountain National forest. It was beautiful but we decided to take the southern route home with the tank. David put us up in his massive 10 bedroom farmhouse and we discovered that he has a theater company (Hampstead Stage Company) as well as the paintball business. David toured us around his facility and we demoed the tanks and I purchased tank #7 and we headed home. 

OSG Notes 9/2019:
The Hampstead Stage company is a non profit celebrating 32 years. (2019) 1-800-619-5302.  David hires professional actors and sends them out in pairs in Priuses to libraries and schools all over the country. His massive barn is full of sets and costumes and was a wonder to behold. 

They are used and hours range from 7 to 14.  Very lightly used. They were imported last year (2018) and stored.  They each have a custom electric sensor so you know when the tank has been hit. Fully set up with dual air tanks and lines. Optional netting.  We identified a couple weak points on the design and remanufactured parts and installed them.  These tanks are an amazing marketing tool and a showstopper .

David included a dual tank Ninja 4500 Nlite 90 paintball system with an Eclipse Emek PAL marker, paintballs and the tank netting.

Here is a list of the OSG modifications:
Added larger gas tank, battery blocks, remote kill switch
Rewelded the control mounts and added steel pins to control sticks
Added two side hit sensors and a sensor computer and hit indicator
Replaced the battery, starter button and added a battery cut off switch
Replaced the wiring with heat resistant wiring
Loctighted lower wheels  (Upper wheels needs some play)
Removed decorative exhaust to improve engine performance
Refinished the back panels

Suggested modifications:
Battery terminal boots
Better fan cooling system
Stronger gas struts

OSG Tank Video:

Trip Home

OSG quoted us $900 to deliver the tank and we did a lot of research to determine the best way to transport it. We wanted to go and see the tank in New Hampshire so we were going to make the trip either way. 

The tank is 6.8 feet long and 3.74’ wide and 4.49’ high. It weighs approximately 1,102 pounds. The tank would have fit in the trucks 8’ bed but the truck couldn’t handle the weight. We looked at Uhall prices and finally took our old trailer which had a ramp. The trailer is 5’x10′ with a GVWR of 2,990 pounds. We had to get the lights fixed on the trailer so it was street legal.

It is 616 miles from Emlenton, where we live, to OSG in New Hampshire. We took two days to make the trip home from New Hampshire to Western Pennsylvania. We discovered that the blue straps (used in shipping the tanks) were not strong enough for the twelve hour trailer ride so we used chain through the front sprockets tensioned with the blue straps. We spent the night at the “Newbury Inn” in Brookfield Connecticut. 

The next day, just after entering Eastern Pennsylvania, we stopped at the Pennsylvania visitors center to recheck the tank. When we looked under the truck we noticed the gas tank was on the ground. A helpful trucker suggested we use a ratchet strap to hoist the tank off the road and we then drove to a nearby garage to get a new retainer for the truck gas tank. What a blessing that the gas tank didn’t rupture. 

As Purchased

When we arrived home, late Friday night, I noticed it had no lights as I maneuvered it off the trailer and parked it in our garage. That weekend I had a bunch of stuff going on at church so I read the manual. Monday, 9/9/19, I put the tank back together. I mounted the two air tanks, the screening, the paintball marker, the hit computer and light. Here is the tank as purchased. (Click on picture for full view.)

Turret Modifications

The first thing I did was remove the netting and the brackets that held the netting frame to the turret. (I wasn’t planning on being a target so I didn’t need the netting) Next, I removed the dual tank system and mounted a single tank inside the turret. I also removed the brain and the hit light, after testing them to make sure I understood how they worked. My first addition was a targeting camera on the canon which required mounting a battery in the back of the turret and a TFT screen in the front of the turret next to the marker. This was followed by a lot of research and documentation.

For the targeting display I used a EXP1250 12v 5ah battery. Amazon cost $17.49. I charge it with a Stanley BC209 tricked charger. Amazon $16.82

For the camera I used a RAAYOO LOO2 backup camera. Amazon cost $16.99. I used this one because it can be configured not to reverse the image. It puts out Yellow RCA video and runs on 12 volts DC. 

For the display I used an old TFT display I had in stock. It measures 6.5” wide by 5” high and had a tripod mount which made it easy to mount to the turret. I used a foam pad. Amazon has one for $29.99 Padarsy 7” 800×480 TFT Display. B Qtec has a monitor and camera set for $27.99.

For the clamps I used Dreamtop 10 pack hose clamps 4.3” for the air tank and battery and 2.5” for the marker. You can get a 10 pack of 5 each for $11.89 from Amazon. They have thumb screws which will break but are nice if you are gentle with them. I used a standard hose clamp for the camera.

Research notes 9/2019

Track adjustment:
Manual suggests 0.4” from mud guard (pressing up)
I measured the Left track at 1” no pressure and the Right at 5/8”

Use 87 unleaded with Stabil which counteracts the ethanol.

Turret battery:
12.85 initial battery voltage
The camera and monitor draw approximately 0.6 amps

Main battery:
12.6 volts initial voltage

The marker is an Etha Eclipse Emek Pal version SN 63002.
They run on approximately 450-550 psi. Use only lithium grease.

Air System:
I purchased some pressure meters and the tank runs 3k psi regulated to approximately 500 psi. The marker seems to leak air but the air line looks good and it has a slide valve which will hold pressure. The tanks need to be retested every 5 years. I’m using an Killhouse Weapons straight remote line with slide check. Amazon $29.99.

I did a lot of searching online for a US version of the struts. They are made by Nitro Struts in Britain NS-FF-10-250-920. (Steel, 9.84 stroke, 21.85 overall, 920 Newtons force (206 lbs). They are expensive ($35ea) as is the shipping ($70). I will check with a local auto parts store.

I tested the marker and it worked well with the targeting camera. I am using .68 caliber winter load. GI Sportz Cryofill Frostbite .68 Caliber approximately $0.025ea

Top Removal

We had to make some special tools to remove the top of the tank. First we made a strut prop (note it rests on the metal frame). Then we removed the struts. Next we removed the prop and lowered the clamshell and then removed the back pins. We designed a hoist bracket and used an electric hoist to remove the top. Again we were careful to only load the steel frame not the fiberglass.

Strut Notes: 9/2019
Rear body pins: I replaced the bolts and nuts in the two back clamshell hinges with clevis pins and cotter pins.
Nitro Struts: I removed the lower screw pin and then unscrewed the strut from the upper bracket.
It is also necessary to disconnect the fans and the side sensors to remove the top of the tank. I rerouted the fan wires around the gas tank so they didn’t hang over the hydro units.

Electrical Mods

 I have made a number of electrical mods to the tank based on my usage of it. I’ve moved control of the tank from the engine compartment to the cockpit. (I understand that in a rental market this may not be wise) I have reconfigured the main power wiring so that battery positive only goes to the main red key switch and it only feeds the starter solenoid and the fuse block. Everything else is after the fuse block. I removed the OSG remote starter module and switched the OSG remote kill switch at the rear panel. 

The cockpit control panel has a key switch to energize and start the engine.  Four toggle switches control the fans, lights, strut lift and the brain. Two twelve volt outlets are provided. One switched by the red main key switch and one switched by the accessory position of the starter switch. LEDs indicate energized circuits. 

I added a large red rubber boot to the positive battery terminal.

The white box on the left is the lift controller. Switch on top.

The controls on the right are the original engine throttle and kill switch. 

Straight Terminal protector boot 4-6 ga $6.99 Amazon.

Switches: Nilight 90014E 12v20a SPST rocker switch with hood. They looked military.  Amazon $9.63 for pack of 5.

LEDs- FICBOX 6mm 12v LEDS. Amazon $9.99 for pack of 5.

Starter Switch Sierra MP41040 15amp 12v. Amazon $16.82
It controls both the engine power (grey) and the start solenoid.

Lights: Yitamotor LED light bar 18w 6” flood Amazon $15.99 for a set of two. I mounted these on the front of the tank body.

Kill switch: I believe that the Kill switches are (closed to stop engine) and therefore in parallel- not in series as shown in the Mk3 manual. OSG added a remote kill switch module to the power panel and I repurposed the fan switch to control the Kill module.

Power panel: note the red boot on the battery and the repurposed remote kill switch power. 

I repurposed the fuse box to include the modifications to the tank. Starter (red) and Fuel (gray) are now handled by one fuse because of the combination starter switch I am using. This fuse also handles the switched accessory 12 v outlet which I use to meter the battery.  

Meter: Lihan Dual USB charger and meter  4.8a. Amazon $10.99
I find this very handy for monitoring main battery voltage.

Lift Mod

The modification that has been the hardest so far has been the addition of a linear actuator to lift the clamshell. While I was researching the struts, I started thinking about ways to lift the clamshell. I researched hydraulics and pneumatics and settled on a linear actuator (motorized screw). I am using one that costs $38 and lifts 900 newtons (225 lbs). To complicate things, I wanted to be able to manually lift the clamshell as well as have the actuator lift it. This meant that only the top of the actuator would be connected to the clamshell. The bottom had to dock into a receptacle. This presents a very interesting problem in three dimensions. It took me four tries before I settled on a bungie cord to help guide the bottom of the actuator into the receptacle. 

The linear actuator is made by Homend GR 9863 12v DC, 225 lbs, 10” stroke, 25 sec full length, retracted length 14.8’, extended length 24.8”,  3 amps. Cost $37.95 Amazon. I picked this one because it closely matched the struts in size and capacity. 

The controller is Eco-Worthy wireless motor controller. (this could also be done with a simple DPDT switch. It comes with a remote control and there is also a manual control on the top of the box. Cost $20.99 Amazon.


Preflight checklist:
Obviously you should read the manual before use. Ear protection.
Check engine and transaxle oil level (1/2 full – don’t overfill)
Walk around checking tracks and suspension.
Verify that the lift strut is in the retracted (DN) position

Operation- Starting:
Check that the fuel is on.
Check that the red power key is on.
Switch on the remote kill if you are using it.
Set the throttle to idle or choke if engine does not start in cold.
Turn the cockpit key switch to on (red light comes on).
Turn the cockpit key switch to start. Engine should start.
Use the fan if it is a hot day (only run when engine is on).
Use strut lift and lights only when engine is running.
Throttle up to fast. (Throttle does not effect ground speed).
Avoid zero speed turns. (control sticks pointed opposite)

Operation – Stopping
Throttle down to idle and run at idle for a few seconds.
Shut down fans and other accessories.
Run the engine at slow speed for several seconds.
Toggle the kill switch until engine stops.
Turn cockpit key to off
Turn red power key to off.
Turn off fuel if not using the tank for a while.

End of day checklist:
Clean mud off wheel bogies and debris from inside tank.
Check grease nipple cap on front hubs is in place.
Check the drive belt for damage. (once the engine is cool)
Check front and rear sprocket bolts are tight.
Check bogie wheels are tight and not damaged.
Leave the clamshell open for storage with the lift strut DN

Nancy and the tank 10/21/19

The Brain

OSG noticed that it was hard to tell when the tank had been hit by a paintball so they designed a hit computer called the Brain. It uses an Arduino type computer and relay board to sense the change in voltage across a pressure sensor mounted on the sides of the tank. When the tank is hit the orange strobe light is latched on by the computer. OSG noted that it is complex and sometimes flaky. It does lend itself to future upgrades like hit counts.

The Arduino board is an Elegoo Uno R3 ($11.96 Amazon) with a 4 realy module ($7.99 Amazon). The orange strobe light is also available from Amazon for approximately $25.00. The system requires a separate 9v battery pack in the Brain case to power the Arduino. Each of the two side sensors is handled independently. 


Let me say up front that I’m an Arduino novice and I don’t have access to the actual programming of the Brain but here is what I can see from the setup. (the Brain is actually an Elegoo Uno R3 – a Chinese Arduino)

Power is supplied to the logic board from a 9vdc battery box which has a small switch on the battery box and a large white switch on the side of the brain case. (The strobe is reset by cycling power (turning the white switch off) to the Brain.)

The two side sensor black leads are wired to the A0 and A1 analog inputs both of which are individually tied to ground through 270 ohm resistor. This is presumably to keep the analog input from floating high. 

The two side sensor red leads are wired to the D2 and D3 digital inputs which seem to be at +5vdc. (They may just be providing a 5vdc source.)

Therefore, I would assume that the analog inputs are measuring the voltage change across the pressure sensor. 

The relay board gets it GND (Black) from the logic board and its Vcc (White) from  pin D8 (digital) of the logic board. This is presumably so the brain can conserve power by turning the relay board off when not in use. 

Relay one of the relay board receives its trigger (Yellow) from D9 (digital) of the logic board. When the SPDT relay is energized it closes the 12vdc path between the tank battery (12vdc) and the strobe light.

Based on the above, I assume that the Brain looks for a drop in the voltage across pressure sensor (a hit) and then latches the relay on. The Brain may also be doing some debouncing of the signal to assure a clean hit. (note: OSG rewired the 12v accessory outlet to be switched by the Brain)

Pressure Sensor

The hit sensor on the tank is made with a Force Sensing Resistor which has IEFSR written on it (Interlink Electronics). They seem to be available on the internet from companies like Digikey for about $12.00. The sensor is 1.5” square and comes with a connector. It is sandwiched between two 7.5” diameter plates of aluminum with a 1/16” thick rubber ring between the two plates. It is held to the tank with two screws and then the joint is waterproofed with a rubber type compound.  The rubber compound can be removed with mineral spirits and elbow grease. When measured installed it varied between 270 ohms and about 1000 ohms. When measured without the cover plate it measures  around 50 ohms to about 100,000 ohms. (A much wider range.) My research shows they are only accurate to about 10% and they seem to give inconsistent results.

Brain Revisited

As an exercise, I decided to see if I could fit the Brain into the orange strobe light. I also wanted to add an adjustment to address the differences in the hit sensors. The sensors tend to trigger on around 270 ohms and off around 1000 ohms but it varies. I chose a Youngneer 12v relay board ($1.50 Amazon) which would fit inside the strobe light and mounted a 1K potentiometer on the top of the light to adjust the sensor trigger point. It doesn’t have the flexibility of the Arduino and you would probably need a relay board and potentiometer for each sensor but it could still all fit in the strobe light.

The black cable is power and the silver cable goes to the sensor
The knob on the top adjusts the sensor trigger point

Laser Conversion

Laser X makes a long range blaster that can easily replace the paintball marker is the tank canon. It’s available from Amazon for about $30.00 and is compatible with other Laser X products. I tested it in daylight at 100 feet and it works great. It comes with an attached target sensor which could be mounted on the tank turret. Unlike some of the smaller Laser X guns its reload function is activated by pulling back the forward stock which works with the mounting shown below. It claims 300’ range which is further than I can see the target.

Remote Control

The tank provides an excellent platform for robotics. My first experiment was to control the two control sticks using the same linear actuator I used in the strut lift system. To accomplish this I needed a remote control that could reverse the actuator. Solidremote makes a nice remote control box for under $20.00.

This is how to wire the Solidremote 202U wireless controller to control a linear actuator to control the tank. Amazon Kit-1 $18.99

  1. Wire the linear actuator to the two relay commons
  2. Wire +12 to the 2 relay NCs and to one relay board power
  3. Wire -12 to the 2 relay NOs and to the other board power

If the actuators works backwards just reverse the actuator connections to the 2 relay commons. I wired the actuator Blue to relay one.

In this setup the actuator stays on approximately 1/2 second after you release the Button. Using the Homend 12v 6” stoke actuator Amazon $35.95 you get approximately 1/4” per 1/2 second pulse.

This is how to program the Solidremote 202U wireless controller to control the right linear actuator. Amazon Kit-1 $18.99

  1. Set the dip switches to 1-off, 2-off, 3-off  (pulse mode)
  2. Hold P1 switch and press Button B (Forward) until sig flashes
  3. Hold P2 switch and press Button D (Back) until sig flashes
  4. Test the relays (LEDs in receiver) and the transmitter Buttons

You program the left actuator in the same way.

You can not use two key fobs simultaneously (eg: pressing a button on each of two key fobs does nothing. (the signals cancel out)

But you can program a button on a key fob to activate both the left and right relay units. Thus pressing A will cause both actuators to move forward and pressing C will cause them both to reverse. 

The actuators are mounted on either side of the seat and connect to the control stick  with a 6mm x 65mm (2.5″) bolt and 2 each 6mm hex nuts. They can be easily removed for manual control. I would suggest using the remote kill system when remotely controlling the tank in case it gets out of control. I used 16g steel from Tractor Supply for the brackets and mounted them so the back clevis pin of the actuator was 10″ from the firewall and the front pin was 11″ above the floor on the control stick. This allows for maximum forward speed and actuator cutoff at both extremes within the arc of the control sticks. It takes some practice to control the tank using the key fob but it works well.

Stay tuned for the winterizing and maintenance sections.

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