Transmission method:
An efficient transmission is key to the success of the project. Several options have been considered:
Right angle gear drives: the configuration of the drive axle and prop location would require the use of two such drives (one low and one high). With the efficiency of these readily available drives hovering in the 85% range, we would see a loss of ~25% of our power to transmission losses.
Twisted belt/Chain: With the drive and prop axles 90degrees to each other, one can twist a V or toothed belt between them. While these belts/chains in straight configuration can be as efficient as 95%, the project advisor's experience has been that twisting the belts as we would need to do for this project leads to significantly higher losses than this.
Spool/Drum drive: In their simplest form, spool drives consist of two drums -- one full of line and one empty. The line is reeled off the full drum and secured to the empty drum. Drive the empty drum and it pulls from the full drum, rotating it's axle. Spool drives when properly configured can be one of the most efficient methods of transferring power from one non-parallel shaft to another. For this reason, human powered aircraft have used them effectively. They have other advantages but also their share of disadvantages.
Advantages:
--- High efficiency
--- Change gearing easily (change size of only one spool)
--- Affect our needed 90d axle offset with no additional losses.
--- Relatively inexpensive
Disadvantages:
--- Limited range
--- Reload or rewind needed between uses
--- Short life span of consumable (strand)
--- One way drive (braking the drive axle will not brake the prop axle)
--- Requires design effor to keep line tight on spool during all operating conditions
The team has ruled out dual gear drives due to power losses. Twisted belt/chain and spool drives are still in the running. We may well design a vehicle which can use a belt/chain drive and switch to spool as a backup if the extra performance is needed.
