# Shell Eco Marathon - Gearbox Problem

**URL:** <https://forums.ipg-automotive.com/t/shell-eco-marathon-gearbox-problem/859>\
**Category:** Powertrain - Electric\
**Tags:** student, carmaker\
**Created:** [10 March 2024 11:19 UTC](https://forums.ipg-automotive.com/t/shell-eco-marathon-gearbox-problem/859 "2024-03-10T11:19:56Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![bbchan](https://forums.ipg-automotive.com/letter_avatar_proxy/v4/letter/b/c37758/32.png) [@bbchan](https://forums.ipg-automotive.com/u/bbchan)\
**Post date:** [10 March 2024 11:19 UTC](https://forums.ipg-automotive.com/t/shell-eco-marathon-gearbox-problem/859/1 "2024-03-10T11:19:56Z")

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Hey! I am working in a university team named ITU Electric Vehicles. We are making an Electric Car for Shell Eco Marathon.

Our vehicle works with a differential system. The engine powers this differential system, but it is not connected to a gear system. When this is the case, we select the no gearbox option in the gearbox section, but this time the program gives an error while running. I have to shift it to automatic every time. After saying no gearbox, I changed the engine torque. I don’t know why it didn’t give an error when I changed the ratio. In the model we use, there is a ratio of 1:11 between the engine and the system. When I enter the ratio as 11 here, the vehicle does not exceed 10 km/h. If I enter 1.1, it goes up to 45, but we are not sure if this rate or speed is correct. I didn’t try entering 0.11. I don’t even know if this method is correct. How can I determine this ratio if the vehicle has no gear and power is transferred through the differential system?

 ![image](https://forums.ipg-automotive.com/uploads/default/original/1X/c8e8d23246eed4f706ded0e4b096741335b35559.png)

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**Author:** ![roberto.ortolan](https://forums.ipg-automotive.com/letter_avatar_proxy/v4/letter/r/96bed5/32.png) [@roberto.ortolan](https://forums.ipg-automotive.com/u/roberto.ortolan)\
**Post date:** [11 March 2024 11:32 UTC](https://forums.ipg-automotive.com/t/shell-eco-marathon-gearbox-problem/859/2 "2024-03-11T11:32:49Z")

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Good morning,

when you select no gearbox, you need to select no TCU(not specified) in the TCU control unit. If you use the ratio in the motor tab you need to modify the max torque at full gas in the control unit, that’s why you see a difference of using a ratio of 1 or 10 since with 10 the max torque at full gas is divided by 10.