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Found 1 result

  1. RC Off-roader with Dual Diagonal Drive I think I'm onto something that will get me through the winter. Summary Dual diagonal drive means: 1) dividing torque over two separate drive trains while 2) preserving the advantage of having open differentials when ´╗┐cornering and 3) passing diagonal tests without using differential locks. Background I have been playing with this idea for a while already, especially after seeing @KevinMoo's dual drive models (Mitsubishi Pajero and Dual-Driveshaft Pickup). @KevinMoo rightfully addressed the vulnerability of LEGO parts in RC models and the fact that using independent drive trains for the left and right sides, loses the benefit of differentials while cornering. This got me thinking. Using independent drive trains for left and right in a 4WD model does indeed drop the benefit of differentials while cornering, but what if we would pair the wheels diagonally, so pair the left front (LF) wheel with the right rear (RR) wheel, and pair the right front (RF) wheel with the left rear (LR) wheel? The resulting 'dual diagonal drive' (I borrowed the term from the electric skateboard scene) would serve two major benefits: While cornering, the LF and RR wheels will average to a speed that is very close to the average speed of the RF and LR wheels. So not having an open distribution by means of a differential between the two drive trains is much less of a problem as with separate drive trains for the left and right side wheels. On a very uneven surface, where one or two wheels may lose contact with the ground, the wheels that do have contact are typically lined up diagonally, see image. With dual diagonal drive, the vehicle would still have traction, even without locking any differentials. Only on slippery surfaces, there are chances of spinning wheels. So this is what I'm thinking of. We start with the basic dual diagonal drive setup: Two separate drive trains, one for the LF and RR wheels and one for the RF and LR wheels. The drive trains cross using two 24t gears and an auxiliary 16t gear that sits right underneath the auxiliary axle for the other drive train. So no clutch gears are involved in this crossing. I inserted a 1L Technic liftarm inside each differential - idea from @Madoca 1977's Toyota Land Cruiser 80 - to prevent the bevel gears from popping out. Next we add a manual locking feature, which closes the differentials with a single lever. This locking feature will force each pair of wheels involved in one of the drive trains to have equal speed. Now we connect each XL-motor to one of the differentials, using a small 4-speed gearbox. That means; two separate 4-speed gearboxes. This may be a bit ambitious, we'll have to see in real-life whether this is feasible or not. I might fall back to two 2-speed gearboxes. I did pay attention to the amount of torque in the transmission though. I geared up the XL-motor outputs and geared down the transmission output. That makes the transmission spin faster with less torque. The gearboxes are operated synchronously using a 90-degree stepper, which is controlled by a Servo-motor. Each gear shift axle has its own 90-degree limiter. And finally the outputs of the XL-motors are transferred to a fake V8-engine via a normal differential. The sole purpose of this differential is to combine the XL-motor outputs for the fake engine. For the steering I'm thinking of using a servo motor. I don't really like the directness of steering with a servo-motor, but the steering link attachment points are moved one stud backwards, which confines the steering angle. This adds to better handling and protects the CV-joints in the wheel hubs. I don't know where this is going to end. I'm not even sure about the exact kind of car I will be targeting, but it sure needs to be some kind of all-rounder. Comments and suggestions are welcome.