Generator Isolation

From DGC Wiki

This is the page for the generator isolation project (see other Fall 2006 Small Projects).

1 Project Description
2 News
3 Contacts
4 Related Articles and Links

Project Description

Overview

We (Daniel Talancon and Nicholas Fette) are going to try and reduce generator vibration effects on sensors and other sensitive equipment. As a measure of progress we will make quantitative measurement of the current vibration in different parts of the vehicle with and without the generator running, and compare changes after design and implementation of any changes.

As of 2006-12-02, the project appears to be at TRL 5.5 or so.

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GOTChA Chart

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Goals

Reduce vibration due to generator affecting stereocameras and LADAR to acceptable level
Determine need for generator remount to aid access to back doors and implement
Document vibration characteristics of generator and its transmission to sensors

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Technical Challenges:

No shop experience, metalworking skills
No prior ALICE experience
No experience with accelerometer
Unclear what "acceptable" level of vibration is
Scheduling conflicts between members and other teams

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Objectives:

[DONE] Nov. 1 Have mounting concepts and data on existing vibration levels
- Several 30-second accelerometer samples for each of the following
  - On one roof stereocamera mount
  - On one roof LADAR mount
- Samples for each of the following conditions
  - With ALICE running, no generator
  - Without ALICE running, generator on
  - With ALICE moving, no generator
[DONE] Nov. 18 Analysis and report on existing vibration data
[DONE]Nov. 21 Have design for changes specified with enough detail to build
[DONE]Dec. 01-02 Initial implementation of new design operational, but not fine-tuned
[DONE]Dec. 05 Have operational mount and a few samples to determine whether any improvement. Ready to present results to team.
[DONE]Dec. 08 Repeat initial measurements and have final paper and documentation.

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Approach:

Work closely with Sensing Team for details on "acceptable" vibration
Obtain accelerometer from Dave Rosen, learn to use from Ken Fisher
Design system to dampen vibration by CAD or by hand
Implement and refine system. Either
- Custom build if able to have shop course
- Hire out construction
Determine possibilities for dampening devices by internet search and asking around

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Relation to System Specification and Architecture

Per Part 1 of the 2007 System Specification,
- Generator necessary for 14+ hours of operation
- Vibration should not contribute significantly to sensor blur
- Vibration should not decrease mean time between failure of equipment

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Vibration Measurement

Our before and after comparison measurements can be seen at Before and After Comparisons. Analysis shows a reduction on the order of 5x to 10x reduction in the generator-induced vibration. We were also able to get the generator-induced vibration to be smaller than the engine-induced vibration in many of the sensors. Our most constraining requirement to not affect the Applanix unit was successfully met with verification by Stefano Di Cairano. We were able to get a steady reading of 0 velocity from the Applanix unit with just the generator on. He also reported a 10x reduction in vibration from the generator and engine combination. Measurements of the vibration were made with an accelerometer (or IMU, inertial measurement unit), the Crista IMU. So far we have taken static measurements (vehicle not moving) on the pre-existing configuration and the new configuration, as well as a few samples with the vehicle in motion on the way to the Rose Bowl and driving around in the Rose Bowl parking lot. These data correspond to respective dates 2006-11-01, 2006-11-19, and 2006-12-01, and are all posted on the project data repository.

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Design and Implementation

We had several choices with which to start:

Replace existing mounting brackets (2 of approx. 12 in by 4 in U brackets made from 1/16 inch steel under generator) with low transmission mount, leaving generator in place
- Barry Mount Controls makes industrial equipment mounts aimed at absorbing low freq. noise from machinery, generators
- Make custom rubber/foam blocks for sandwich mount
Remount entire mounting cage and remount generator with damping suspension cables
Scale down to military generator and fit under vehicle where batteries are now (passenger side). This would require locating a smaller form factor generator that provides the same power as the current Honda EU3000is (generator), moving the batteries (probably to inside the vehicle), moving the external fuel tank, etc. This would make ALICE look prettier, too.
Replace ALICE the Smart Car with Alice the "Smart car" with lots of extra room for generators. This would make ALICE look more European, too.

After consideration our choice was to obtain industrial grade machinery damping/mounting devices from Barry Controls Part # 633A-60 in order to replace the existing four bolts with rubber washers. On 2006-12-01 we made the change to the new damping system. This required

removing the generator from ALICE (disconnecting NEMA L5-30P power cable and fuel line),
drilling eight new holes in the generator cage platform (two for each dampener, about 0.4 inch diameter),
enlarging existing holes in generator feet plates (four holes, enlarged from about 0.4 inch diameter to about 0.5 inch diameter),
replacing generator (and cables) and tightening new mounts.

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News

Meeting: Monday, 2006-12-04, 4:00 pm, in the shop
- Purpose: determine vibration on Applanix wheel unit.
- Notes: Stefano showed us readings from the Applanix on his laptop. Before the new generator mounts, when both the engine and generator were running, the state estimate would jump around within a box of about 20 cm on the side with the vehicle stopped; after the new generator mounts, when both the engine and generator were running, the state estimate would jump around within a box of about 2 cm on the side with the vehicle stopped, comparable to running just the engine. In terms of errors, this is a ten time reduction, and the generator vibration on the Applanix is satisfactory. However, it would still be nice if the engine vibration were reduced. We do not anticipate solving this problem, at least not in any simple manner.
Meeting: 2006-12-01, after dinner, ALICE shop
- Purpose: implement design changes, ie, install new damping devices.
- Notes: talked to Stefano, installed dampeners, noticed high-pitched sound near right rear corner of ALICE while running engine, repeated most measurements per 2006-11-01. At first glance the generator vibration appears greatly reduced.
Parts update: Ordered from MJ Vail Company (1-800-526-6003), possibly in as of 2006-11-30.
Meeting: 2006-11-19, ALICE shop, then Rose Bowl
- Purpose: take some more measurements with Alice driving
- Notes: data posted here
Data update: visit nfette's directory to view and download data files from IMU measurements (2006-11-01).
Presentation: 2006-11-06
- Image:Generator Isolation Prelim Review Presentation.ppt
- Notes: Suggestion from the audience that acceptable level of vibration be defined such that calibrated sensors do not become uncalibrated during expected operational time spans (such as 14 hours). Also, Daniel is contacting Barry Mount, and Nick is posting .csv, .xls, and .png data (probably in an archive) sometime soon.
Meeting: 2006-11-05, early afternoon, lunch or something
- Purpose: Finish data analysis, prepare presentation
- Notes: Produced a design review presentation
Meeting: 2006-11-01 3:00 PM at shop
- Purpose: same as last attempt
- Notes: we had success at taking measurements on ALICE with the Crist IMU today. We took 30s samples at 60Hz on each of {front bumper center, front bumper left mount, road-finding mount, rear bumper center, and generator platform} with each of {all systems off, generator on, engine on, and both on}, and one sample on the {generator} itself while running. Data is posted on gc: /home/users/nfette/public_html/gen-isolation/ (as of 2006-11-17).
Meeting: 2006-10-30 3:00 PM (maybe: see Alice Scheduling)
- Purpose: retry making initial measurements, discuss methods some more. Stiffening existing generator mount box will help in case we mount a sensor on it -- anyhow, sensor team needs to know what they can do in the back. Can vibration isolaters made from elastomers hold up in all weather conditions?
- Notes: Alice did not return from Ford by 6:00.
Sensor Mount Expansion needs to put another LADAR unit on the rear bumper or generator mount. We should look into small military generators we might mount underneath the chassis, and measure vibration on the generator mount when we get the accelerometer.
Meeting: 2006-10-27 3:00 PM, Steele 12 (the lab).
- Purpose: make initial measurements of vibration, log and post data or analysis. We will find and use accelerometer via serial cable to Windows laptop. Need to bring power supply for unit.
- Notes: We met, didn't find the accelerometer, discussed Barry Mount industrial vibration isolators. Decided to meet Monday. Ken came in about 5:00-ish, showed me where the IMU was (drawer by door). More details about IMU below.
First meeting 2006-10-19