2 speed automatic car - Ramp Test

[TechnicBrickPower]

 

My 2 speed automatic gearbox is put to the test by incorporating it into a 2 speed automatic car. This gearbox implements a number of design principles aimed at improving the gearbox performance - namely of placing the torque detector on a separate path to the main gearing power path to reduce torque and power losses in the gearbox, and using gear disengagement to switch gears instead of gear engagement.

A simple derivation is presented of the physics involved in driving up a ramp in order to determine the amount of additional torque required at the motor output to be able to overcome the gravity and the corresponding potential energy.

The torque of a large power function motor is measured by measuring the output axle speed using a laser tachometer and relating that to the linear torque/speed relationship of the motor. These measurements are demonstrated for the car without any loading and with simple horizontal motion.

Finally the car is put to the test by attempting to drive up a 40 degree ramp.

 

 

[BrickBuildingFox]

This is fantastic! Thanks for sharing the journey of developing the gearbox and improving it step by step. I'm a big fan of your scientific approach to lego technic.

[arjan400016]

Like brickbuildingfox said:

It's great to see something like this being developed en getting better and better.

[Glaysche]

I have loved following this series.  Applying theory to lego mechanics is very interesting.

[Woodpecker]

Excellent series! I am getting better at physics and math from your videos. 

[TechnicBrickPower]

On 12/12/2020 at 8:58 AM, Woodpecker said:

Excellent series! I am getting better at physics and math from your videos. 

 

On 12/12/2020 at 7:39 AM, Glaysche said:

I have loved following this series.  Applying theory to lego mechanics is very interesting.

 

On 12/12/2020 at 7:03 AM, arjan400016 said:

Like brickbuildingfox said:

It's great to see something like this being developed en getting better and better.

 

On 12/11/2020 at 10:44 PM, BrickBuildingFox said:

This is fantastic! Thanks for sharing the journey of developing the gearbox and improving it step by step. I'm a big fan of your scientific approach to lego technic.

 

Thanks everyone for their encouraging comments. Hope to keep ideas flowing!

[allanp]

I have recently watched your whole series of videos and they are great. I look forward to seeing more.

I do have a question/possible suggestion. The torque sensing devices seem to sap some power away. Is it possible to allow the motor itself to rotate, and you use the rotation of the motor to sense how much torque is there? That way the torque sensing doesn't go through the drive train at all. 

I've been watching with great interest as I want to start MOCcing again, and I'd like to start with a large 4x4 vehicle with automatic gearbox, with lots of gears. Which leads me to another question.

What would happen if you take multiple copies of your most efficient design of 2 speed gearbox, set them to change at different levels of torque, and use differentials to add their outputs together. Would it mean that two gearboxes would give you 4 speeds, and 3 gearboxes would give 8 speeds (2x2x2)?

[BrickBuildingFox]

1 hour ago, allanp said:

Is it possible to allow the motor itself to rotate, and you use the rotation of the motor to sense how much torque is there?

There is the linear relationship between the RPM of the motor and the torque. The new powered up motors have a rotation sensor to measure speed. This can be utilized for torque detection and control of another motor to change gears. I assume that LEGO uses this in the Volvo 6x6 (set 42114), which has the automatic 3-speed gear box. This would be straight forward solution and very comfortable for a RC-car. I attached a small "Powered up"-program it shows the current speed of the motor in variable "a". It decreases, as the load increases and thus "a" could be used with a if-condition to drive the gear switching motor.

[allanp]

1 hour ago, BrickBuildingFox said:

There is the linear relationship between the RPM of the motor and the torque. The new powered up motors have a rotation sensor to measure speed. This can be utilized for torque detection and control of another motor to change gears. I assume that LEGO uses this in the Volvo 6x6 (set 42114), which has the automatic 3-speed gear box. This would be straight forward solution and very comfortable for a RC-car. I attached a small "Powered up"-program it shows the current speed of the motor in variable "a". It decreases, as the load increases and thus "a" could be used with a if-condition to drive the gear switching motor.

Potentially yes. I don't think 42114 actually utilizes that, it just changes up at a fixed rate. But yes maybe a program could be made that monitors motor RPM to sense when to change gears. I really hate coding though! And I'd like to use multiple buggy motors.