We are now interested in the design of a space constrained gear train, suitable for usage in the hostile atmosphere of the earth's twin, Venus. As suggested by [1], the corrosive atmosphere and high temperatures prevent a majority of currently used electronic devices from being used in Venus. Consequently, we go for a mechanical device with use of Ti-6Al-4V Grade 5 Titanium, as suggested during the hackathon. The material data is listed in links [2] and [3].

A preliminary strength based design is considered in the link: here . The part list and weight of the gears are mentioned in the link below: .For an overview, only the kinematics of the mechanism is described for brevity.

The assembly drawing,1st angle projection is given here:

Assembly drawing, Part Count and Weight List: Part Count

In our system design, we have used a total of five gears and a rack-pinion to achieve reversal through an external spur gear mechanism. While inspired from traditional automobile manual gear shifting systems, it is significantly better space-optimized, as evident from the fact that the gears are all fixed to the wall and the lengths of the input and output shafts actually covered up by our system is not much compared to a car transmission.

To account for both reliability and wear, we have avoided the use of clutches and brakes, which are to a large degree, friction dependent. This is due to the fact that unlike commonly found situations, our system transmits high-torque and low speed. The speed cannot however be increased drastically though through a gearing mechanism, as even in engineering practice, the limiting velocity ratio is around 4:1, and even then, our calculations found out that it is infeasible to take a high velocity ratio without significantly increasing the size of the larger gear, consequently increasing the weight.

Here is a sketch of the Rack-Pinion Setup:

A sketch of the Rack and Pinion Arrangement

When the rover moves forward the power is transmitted through the gear train: G1-G3-G5. When the reverse is desired, a pinion is used to drive two racks. The Gear G3 gets disengaged and the gear G2 gets engaged with the gear G4, which however, is in constant mesh with the gear G1. Consequently the power is transmitted according to the train G1-G4-G2-G5. The pinion is moved in the reverse by a certain angle to get the rover moving up front again.

Further avenues of improvement:

1. Please observe the article on gear placement: here. Optimizing the pinion placement is an interesting future prospect. An even better technique will be to use the logic gate mechanisms enumerated in [1](pg. 19, pg. 24). This permits elimination of the large pinion gear(improving weight efficiency) and much better integration into a mechanical computer, albeit with increased shocks and bending.
2. Usage of springs to 'bias' the gears, by connecting suitable springs to the rack holders. This way, a default connection can be maintained in the absence of signals.
3. Optimizing the gear body shapes so as to enable use of better velocity ratios, say 3:1.
4. Usage of magnetic dampers/inductors to better control motion of the output shaft and the idler gears.
5. Testing of Chain-Sprocket Mechanisms to try and utilize the large space available.

References used:

1. https://www.nasa.gov/feature/automaton-rover-for-extreme-environments-aree and https://www.nasa.gov/sites/default/files/atoms/files/niac_2016_phasei_saunder_aree_tagged.pdf
2. https://www.upmet.com/products/titanium/ti-6al-4v
   
3. http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTP641
4. Bhandari, V.B.3rd Edition. Design of machine elements. Tata McGraw-Hill Education.
5. Shigley, J.E.,Shigley's mechanical engineering design. Tata McGraw-Hill Education.
6. Rattan, S.S., Fourth Edition. Theory of machines. Tata McGraw-Hill Education.

#machines, #Gear Drives, #Kinetic Chains, #Mechanized Control of Drives.