M5 Stuart Tank R/C Conversion

Back in January of 2006 when the stores were clearing Christmas items, Ken Gracey of Parallax Inc picked up this tank for a mere $25.00 on clearance. Knowing that I was looking for a platform larger than a BoE-Bot to experiment on with some GPS and servo turret controls he dropped this beast on my desk.

I had some ideas in mind when I opened this thing up to find out that it was powered by a 7Ah Sealed Lead-Acid battery. Immediately the wheels (tracks) started turning on what I could do with this thing and the longevity it probably had. But first there was work to be done.

Opening this tank was pretty straight forward and easy. If you’ve taken anything apart before and have a Phillips screwdriver you’re set. When I first removed the top, the weight of it reminded me that the SLA battery was actually stored in a compartment in the top half. I had to remove a retainer bracket to actually take the battery out since the battery was designed to be left in place. Charging was done through the power cable.

There were three wires coming from the top half to the base of the tank. The Black / Red pair was the main power cable from the battery and had a quick-disconnect. The other two sets of wires were for the turret. The 2-wire cable was the turret rotation motor and was literally direct-connect. The turret does implement a mechanical stop (much like a standard servo) though. The 3-wire cable was for the turret firing system which fired a plastic dart type projectile.

Once the wires were disconnected the top could be completely removed and was subsequently dissected with the intentions to refit the turret with tracking sensors and possibly an Airsoft gun. At one point I experimented with dual PING))) sensors for target tracking and was thinking about adding a thermal array for tracking heat sources (such as people).

Inspecting the motor / gearbox assembly you could see a relay control board behind the motors.

This explained the jerky full on/off motion of the tank by default. This also put undue stress on the motors, gears and treads.

I removed the gearbox assembly to grease it and test the motors.

Each motor was fitted with not only three (3) noise reducing capacitors, but an inductor on each power lead as well. I was amazed at all the attention to motor noise, but then to have a relay control board instead of a solid-state H-Bridge! Some of the photos in this section were borrowed from the internet since I lost some of the photos from my tear-down when the website crashed. I left the credits in the photos so you can check out the photographer’s site.

On the belly there were two removable plates which exposed two HUGE underbelly compartments.

These compartments were completely empty but I saw them as being able to hold pressurized air, extra batteries, extra circuit boards or anything else I might want to add. As a test I dropped a 12V, 7Ah SLA battery into one and a stack of 3 Super Carrier Boards into the other. Oh yeah, got room?

The first thing I worked on changing was the motor control system from a relay board to using two HB-25 motor controllers.

These provided proportional DC motor control with the simplicity of driving a continuous rotation servo. Each HB-25 was mounted from the side and had plenty of room for air underneath with the bonus being the front of the case had a vent. As you can see I also added a front Sharp IR sensor to detect if the tank was going to run into something too low for the other sensors to see. All the wires were passed back to the new control board in the belly.

Once the tank was up and running on its own I took it out in the field near Parallax Inc. to test how well it could handle obstacles. As you can see, branches on the ground were no issue at all, nor was tall grass.

Here I am also posing with the tank for a magazine advertisement and article on the HB-25 motor controller.

The photo above is one I found while searching the internet trying to find more info on this tank. I found many sites where different people had gotten one of these tanks and wanted to modify it. There were even some highly detailed breakdowns on some sites showing the position of every screw and what each part on the main control board did. I applaud those who put some much effort into it only and shared it with the rest of the world.

Ultimately though I wired up an R/C radio system so I could override whatever the tank was doing. I never finished the turret tracking and the firing mechanism stopped working at some point. Besides I had lost the only two darts that came with it anyway.

Abandoned?

So…why did I abandon the project? I know you’re probably wondering now after reading about everything I did. Well, first I moved on past the tracking into autonomous roving and I wanted to add GPS capability. I posted a clip of the tank navigating through the field using GPS, but with the tall grass and the slow movement of the tank all I got for feedback was some negative comments about how much more fun it was watching paint dry.

Around this time I also acquired a mid-sized robot chassis and started working on a proof of concept of what would later become the Stingray Robot Kit. So my focus shifted and I never went back to the tank. The new chassis had a 4-motor skid-steering system similar to the tank, but without tracks. Being such a big beast I decided I couldn’t just leave the tank lying around so I gave it to someone else who, at the time wanted to work with it. I’m not sure what, if anything he ever did with it. As for me, I’d still like to build a tank-tread robot some day. But then I will want to use larger scale tank treads that I can get parts for if something breaks. Yes, I do break things myself occasionally.

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