Questions about Tank-building

[z3_2drive]

For my next build I am planning to make a high-speed RC offroad tank with 4 buggy motors, similar in design to a Ripsaw. This will be my topic for any questions/discussion that may come up during the build. My recent BL orders have yet to come, so for now I only have one question.

Are drive motors located at only one end of the vehicle? Or can they be placed at both 'axles'?

It would seem simpler to have only the rear end driven, or would it be better to evenly distribute torque and avoid stress at one end?

[allanp]

In real life tank tracks are driven by either the front or the rear sprockets, never both front and rear so I guess there is little or no advantage to having all sprockets driven.

[Sariel]

From my experience, driving both ends doesn't work as well as one could think. I suppose the track isn't the best way to sum the torque delivered to two different sprockets, perhaps because it's flexible and sensitive to differences between these two sprockets' speeds.

[Gee]

The vast majority of actual tanks (as opposed to tracked armoured vehicles that poeple mistake for tanks) are driven from the rear. I'm pretty sure that driving the track from the rear gives better traction, something to do with the drive wheel only having a short distance of "slack" track (the bit between the drive wheel and the floor) to pull. If it was front driven it would be pulling "slack" track the entire length of the vehicle.

Crap explanation, but then again, I'm no engineer. In the words of Oddball "I just ride 'em, I don't know what makes 'em work".

Edited January 3, 2014 by Gee

[Rijkvv]

I'm fuzzling about building a tank as well. Something I might try in the future is one of the tracked vehicles from the Thunderbirds, and due to limited space it can be useful to divide the motors to the front left and rear right sprocket. It's not realistic however.

If I'm correct the Russian BT tanks were all-wheel driven and if a track was lost could change between skid-steer and regular steering. Sariel, maybe a nice challenge to you?

Edited January 3, 2014 by Richie

[DrJB]

The vast majority of actual tanks (as opposed to tracked armoured vehicles that poeple mistake for tanks) are driven from the rear. I'm pretty sure that driving the track from the rear gives better traction, something to do with the drive wheel only having a short distance of "slack" track (the bit between the drive wheel and the floor) to pull. If it was front driven it would be pulling "slack" track the entire length of the vehicle.

Crap explanation, but then again, I'm no engineer. In the words of Oddball "I just ride 'em, I don't know what makes 'em work".

Well, it is true that 'most' tracked vehicle are driven from the rear, with the sprocket at the rear and idler/track-tensioner at the front. However, there are machines with a single/central sprocket in the middle (top) and two idlers (front/rear) as in some of the Dozers made by CATerpillar.

Edited January 3, 2014 by DrJB

[z3_2drive]

Thanks, that's what I'm going to do, 4 buggy motors situated at the rear, 2 left, 2 right, and battery+electronics box near the front to balance weight.

[z3_2drive]

Sorry for double-post, but I was inspired to build this custom-RC tank after seeing this video:

If that is what 7.4 Volt looks like, I wonder what my 11 Volts will do

[Rijkvv]

The vast majority of actual tanks (as opposed to tracked armoured vehicles that poeple mistake for tanks) are driven from the rear. I'm pretty sure that driving the track from the rear gives better traction, something to do with the drive wheel only having a short distance of "slack" track (the bit between the drive wheel and the floor) to pull. If it was front driven it would be pulling "slack" track the entire length of the vehicle.

In addition to that, it also has to do something with the driveshafts. In most tanks, the engine is mount in the rear. When it is front-driven, the driveshafts force the turret to be mount higher, something that can be seen at German and American WW2 designs. Note the difference in height between the front-driven Sherman and rear-driven Pershing for example.

[Sariel]

The tank's engine placement is actually important for combat. Many mid-WW2 German tanks had engines in front, and the result was engine and/pr transmission damage whenever the front armor was penetrated, often resulting in catastrophic fire or at least immobilizing the tank completely. In the Tiger tank, for example, the engine was moved to the rear to make the tank harder to kill. Today almost all MBTs have rear-mounted engines, but there still are exceptions such as the Merkava which was designed with focus on crew survivability, so the tank has front-mounted engine and an escape hatch in the back of the hull.

I don't know about the driveshafts thing. All front-driven tanks I know have front-mounted engines. This has no impact on the turret height, except that the turret is sitting closer to tank's rear end.

Edited January 3, 2014 by Sariel