I just watched a video of 4 trucks connected together pulling a huge load. Then there were 3 more trucks connected to each other and the load pushing.
How do the 7 trucks synchronize so that they work together as one unit? Could one truck could have a negative effect on all the other trucks if it went slower?
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Only if it contributes less torque than it would take for it to roll at the speed the load is going. Imagine the following:
Let’s say the load is rolling at 10mph, and any one of the 7 trucks involved would require 10% throttle to roll at 10mph on its own. But the load is heavy, so it takes 7 trucks 40% throttle input to roll the load at those same 10mph. If one of the 7 trucks input 10% throttle instead, they wouldn’t be contributing to pushing the load, but they wouldn’t be making it worse. 6 trucks at 40% would not be better than 6@40% + 1@10%. If one of them was to, however, let off the throttle entirely, now the other six would have to push the idling truck around to, so 6@40% + 1@0% would be worse than 6@40% + 1@10%. Having said all of that, 6@40% + 1@10% would not result in the load rolling at 10mph, because we already established you need 7@40% to get that.
They don’t have to be perfectly in sync for each of them to apply force to the load to get it moving. Sure, you’ll lose some effectiveness if they’re not all pushing at exactly the same rate, but they’re all contributing more than not, unless someone’s fully locked up and standing on the brakes 🙂
When a driver pushes the throttle (gas) pedal down on a vehicle to a certain position, they are not setting the speed that the vehicle will go. They are more or less setting the power that the engine will put out. The vehicle will go whatever speed is necessary to use that much power.
Say you are driving on flat ground at a constant 50 km/hr. If you hold the throttle pedal in the same position and start up a hill, the car will slow down — maybe to 30 km/hr. If you then go back down the hill (with the same throttle position), the car might speed up to 90 km/hr.
Likewise, with two trucks, if the trucks start out at the same 1/2 throttle position, they will both push the same amount (50%, 50%). Now if one truck stays at 1/2 throttle and the other goes to full throttle, then the full throttle truck might increase to doing 60% of the pushing, while the 1/2 throttle truck drops to 40%.
This natural tendency of engines to to adjust to the output speed needed (within limits) means precise matching of the throttle position by the drivers is not needed. As long as they generally agree on the speed they want to go (I’m sure practice helps), then the engines will automatically take care of any small discrepancies.
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