Difference between revisions of "RC15Motors&Gears"
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Below are the settings we used to cut the delrin gears with reasonable accuracy. | Below are the settings we used to cut the delrin gears with reasonable accuracy. | ||
| + | |||
| + | ==== Our primary material to laser cut was delrin. That's because delrin exhibits nice properties in terms of strength and smoothness. It also cuts nicely when the proper settings are determined. ==== | ||
==== Delrin ==== | ==== Delrin ==== | ||
| Line 157: | Line 159: | ||
| style="width: 41px;" | Black | | style="width: 41px;" | Black | ||
|} | |} | ||
| + | |||
| + | |||
| + | |||
| + | This was followed by a cut at the following settings: | ||
| + | |||
| + | {| border="1" cellspacing="1" cellpadding="1" style="width: 500px;" | ||
| + | |- | ||
| + | | Etch/Cut? | ||
| + | | Cut | ||
| + | |- | ||
| + | | Line Thickness | ||
| + | | Vector | ||
| + | |- | ||
| + | | Power | ||
| + | | 90 | ||
| + | |- | ||
| + | | Speed | ||
| + | | 6 | ||
| + | |- | ||
| + | | PPI/Hz | ||
| + | | 1000 | ||
| + | |- | ||
| + | | Passes | ||
| + | | 2 | ||
| + | |- | ||
| + | | Lens (Black/Red/Blue | ||
| + | | Black | ||
| + | |} | ||
| + | |||
| + | The two cut lines in the end are necessary to fully remove the gear. We speculate that's because the etching process does a coarser number of pulses. We hypothesize that increasing the PPI/Hz may help prevent edges that remain on the part afterwards that require cutting. | ||
Revision as of 17:21, 11 January 2015
The robots for the 2015 RoboCup SSL competition utilize new 50 Watt brushless motors from Maxon Motors. The previous two fleets of robots designed and built by the teams used 30 Watt motors, also from Maxon.
Contents
Background
2008 Robot Fleet
The 2008 fleet of robots utilize a 30W Maxon Motor. Power was transmitted through a spur gear fixed to the shaft. This spur gear is held in place by a set screw that was set onto a flat grinded onto the shaft. There are no encoders on these robots.
Performance
These motors perform fine to this day (several years later). However, the lack of encoders makes it difficult to control the robots with any degree of precision.
2011 Robot Fleet
The 2011 fleet of robots utilize the same 30W Maxon Motor. Power was transmitted through a spur gear built into the motor shaft. The custom shafts were outsourced, and were effectively pinion wire that was turned down on a lathe to have appropriate sizing for:
- Pressing the shaft into the brushless motor shell
- Pressing an encoder wheel onto the end of the shaft
- Terminating the shaft such that the encoder housing could be capped and kept undisturbed from outside elements
Performance
These motors perform extremely poorly due to the in-house manipulation. Due to errors during the team's manufacturing process in previous years, the brushless motor shell can slip on the custom shaft (i.e. the press fit is not strong enough to prevent slip), thereby degrading power transmission. This was rectified to an extent by epoxying the shaft onto the shell. However, this process is messy, inconsistent and sometimes results in deformation of components when assembled, thereby degrading the motors even further.
The 2011 robots suffer from hall faults due the misalignment of components, and the fleet is largely unusable due to these problems. However, the encoders do prove to be useful if the robot has little to no motor issues.
Requirements
The motors and drive gears of the 2015 robot fleet is intended combine the good aspects of both the 2008 and 2011 fleets, without any of the problems. These requirements are as follows:
Primary requirements
- The team should not have to disassemble the motors in order to assemble the drivetrain. (The 2011 robots required a custom shaft, which required pressing combing apart and then reassembling. This results in degraded performance due to a variety of issues).
- No epoxy to be used anywhere in the process
- Any motor shaft manipulation should be able to be done safely and easily on in-house equipment
- Compact design following that of the 2011 robots, as the large 50W motors do not permit such broad drive module as seen in the 2008 fleet.
Secondary requirements
- The gears for the drivetrain are manufactured in-house on either the laser cutter, waterjet cutter, or injection molding machine
Testing and Prototyping Gears
Waterjet
The two main materials cut via the waterjet have been aluminum 6061 and mild steel. For aluminum, we tested 1"x2" squares to understand the taper produced by the waterjet cutting process. The results are below:
Steel - 0.117" thick
| Trial 1 | Trial 2 | Trial 3 | |
| Waterjet set thickness | 0.117" | 0.130" | 0.117" |
| Taper compensation? (Yes/No) | No | No | Yes |
| Estimated time to cut (minutes) | 0.583 | 0.636 | 0.938 |
| Measured dimension on top (Nominal 1") | 0.9937 | 0.9877 | 0.9945 |
| Measured dimension on bottom (Nominal 1") | 1.0016 | 1.0002 | 0.9931 |
| Resulting Taper (degrees) | 1.93 | 6.25 | 0.342 |
Estimated time for cutting one of the motor gears: 1.6 minutes
Aluminum - 0.125" thick
| Trial 1 | Trial 2 | |
| Waterjet set thickness | ||
| Taper compensation? (Yes/No) | ||
| Estimated time to cut (minutes) | ||
| Measured dimension on top (Nominal 1") | ||
| Measured dimension on bottom (Nominal 1") | ||
| Resulting Taper (degrees) |
Laser Cutter
Below are the settings we used to cut the delrin gears with reasonable accuracy.
Our primary material to laser cut was delrin. That's because delrin exhibits nice properties in terms of strength and smoothness. It also cuts nicely when the proper settings are determined.
Delrin
| Etch/Cut? | Etch |
| Line Thickness (if any) | 0.001" |
| Power | 90 |
| Speed | 4.5 |
| PPI/Hz | 1000 |
| Passes | 25 |
| Lens (Black/Red/Blue) | Black |
This was followed by a cut at the following settings:
| Etch/Cut? | Cut |
| Line Thickness | Vector |
| Power | 90 |
| Speed | 6 |
| PPI/Hz | 1000 |
| Passes | 2 |
| Lens (Black/Red/Blue | Black |
The two cut lines in the end are necessary to fully remove the gear. We speculate that's because the etching process does a coarser number of pulses. We hypothesize that increasing the PPI/Hz may help prevent edges that remain on the part afterwards that require cutting.
