Team Invincible at UoW Engineering Info Night in Jan, 2010

Team Invincible was invited to the University of Windsor’s Engineering Info Night on Jan 7, 2010 at the Automotive Research and Development Centre (ARDC), to showcase the robots.

Machining encoder shafts for NPC DC motors: NPC-T64 or NPC-T74

- Prepared by Matthew Hurajt, Team Invincible 2009-2010

This post describes how to install the optical incremental encoders on the NPC DC motors: NPC-T64 or NPC-T74. The only viable location to mount the encoder is directly to the back of the motor shaft. The shaft has a small hole with diameter 0.0815” and a depth of at least 0.125” inches in the dead center.

The small hole in the motor’s shaft

The encoders were purchased from US Digital, and requires a shaft with a diameter of 0.1875”.

The encoder in its housing

The encoder wheel accepts a 0.1875” diameter shaft

The chosen solution was to extend the shaft by machining a piece with a small stub to be pressure fit into the small hole in the back of the motor shaft. A shoulder is included to steady the extension.

3D View

2D Drawing-Encoder Shaft

Download the CAD files for the encoder shaft (Size: 407 KB)

Dimensions for the spacer plate:

3D View of spacer plate

2D Drawing of the spacer plate

Download the CAD files for the spacer plate (Size: 409 KB)

Equipment:

Bridgeport Milling Machine	Technical Support Center, University of Windsor, Ontario
Harrison M300 Horizontal Lathe (13″ x 40″)	Technical Support Center, University of Windsor, Ontario
Carbide Cutter	Technical Support Center, University of Windsor, Ontario
Cut off tool used for parting	Technical Support Center, University of Windsor, Ontario
Collets are used to securely hold small diameter round pieces	Technical Support Center, University of Windsor, Ontario
The drawbar threads into the collet from behind and secures it into the holder	Technical Support Center, University of Windsor, Ontario
The micrometer is used to get a precise measure of the diameter of the piece while it is being machined in the lathe.	Technical Support Center, University of Windsor, Ontario
The jewel indicator is used to find centers and ensure that the shaft is spinning true.	Technical Support Center, University of Windsor, Ontario
Hammer	Technical Support Center, University of Windsor, Ontario
Jack screws are used for support of the motor on Bridgeport	Technical Support Center, University of Windsor, Ontario
Brass collar used to provide even pressure while pressing in shaft	Technical Support Center, University of Windsor, Ontario
Power supply used to turn the motor and check for wobble	Technical Support Center, University of Windsor, Ontario

Materials Required:

10-18 hot rolled mild steel, appox. 0.518 “ in diameter

Essex Metals, Oldcastle, Ontario

Raw material: 10-18 hot rolled mild steel, appox. 0.518" in diameter

Steps

1. Mount a piece of stock ½” diameter mild steel directly into the collet and into the lathe.  Use the drawbar to secure the collet holder from behind.
   

   Collet mounted in the lathe

   Raw material mounted in the collet

2. Face  the piece and set the digital readout to zero.
   

   The bar is faced for a good finish and to allow proper measurement of the rest of the dimensions

   The z-axis (the length of the lathe) is zeroed to the freshly cut face

3. Score in the reference marks that correspond to the different diameters across the part, precisely using the digital readout.
   

   These marks are just for visual reference.

4. Turn down the shaft to size at 1200 rpm.
   

   The cuts are made shallow, about 20 thou, to ensure they are smooth

   The shaft is turned down to its finished diameter plus about half a thou for polishing

5. Polish the shaft.
   

   The micrometer is used to measure precise diameters

   Sandpaper (220 grit) is used to polish for a smooth finish

6. Turn down the shoulder to approximately 0.5”.  This dimension is not critical and it is polished just for aesthetics.  The piece is then parted at 800 rpm using the cut off tool.
   

   The shoulder is turned down

   Parting the piece

   The separated piece after parting

7. Mount the piece the other way around in the lathe using a smaller collet.  Face the end and the turn it down to the stub for pressure fitting into the motor shaft. Polish it like before.
   

   The bottom is faced

   The stub is turned down

   The finished piece

8. Mount the motor in the Bridgeport milling machine.  Use the indicator to center it.
   

   The motor is mounted in the vice and the jack screw is used for added support to the odd shape of the motor

   The motor is centered using the indicator

9. Place the extension shaft into the hole.  Put the brass collar on top so that the Bridgeport can be used as a manual press to force the piece into position.
   

   The shaft placed in

   The shaft pressed in

10. Connect the motor to the power supply. Gauge the wobble with the indicator. Make minor adjustments with the hammer.
    

    Setup to run motor

    Indicator to check wobble

    Minor adjustments with the hammer

11. Add a plate to the motor housing to place the encoder above the shoulder.  The plate is made from aluminum and machined to shape on the Bridgeport mill.  It is fastened securely into the motor using two small machine screws.  The encoder is placed on the shaft, the housing secured by the adhesive.

Tapped holes in the housing to secure the plate

The plate is 0.255” thick

The mounted encoder

Join the Team for Intelligent Ground Vehicle Competition (IGVC) 2010!

IGVC 2010 Competition

We are actively recruiting to build an inter-disciplinary team from mechanical, electrical, computer science and business faculties, in order to build a robot for the Intelligent Ground Vehicle Competition (IGVC) 2010. This is one of the toughest international competitions with over 40 teams competing in 2008, and over 50 in 2009. The aim is to build an autonomous off-roading robotic platform which can navigate around natural and man-made obstacles in the shortest amount of time. Design and construction of an Intelligent Vehicle fits well in a two semester senior year design capstone course, or an extracurricular activity earning design credit. For more information about the competition please visit (http://www.igvc.org) The current budget estimate is around 20-30K. If you have any one or more of the following skillsets, please feel free to get back to us:

• Overall Mechanical Design including suspension design for an off-roading vehicle (involves making CAD drawings, running simulations, FEA analysis, etc.). Machining, welding, milling, and painting experience is also great to have.
• Sensor interfacing including GPS, Digital compass, LIDAR, cameras, ultrasonics, Inertial Measurement Units (IMU), and Quadrature optical/hall-effect wheel encoders. (familiarity with Serial protocols and C++/C#/VB programming experience required).
• Power distribution and battery management (familiarity with various battery chemistries, fuses, chargers, protection circuitries, and DC-DC converters required)
• Business students only: Fundraising, public relations, graphics design (brochures, posters), event planning, logistics and support.

Contact Us

If you are interested in joining the team, please contact:

Siddhant Ahuja (Sid)
Team Lead
Rm. 219 Essex Hall,
401 Sunset Avenue,
Windsor ON, N9B3P4
E-mail: ahuja5<At>uwindsor.ca
Phone: +1-519-253-3000 ext. 4860
Fax: +1-519-971-3695
Web: http://uowteaminvincible.wordpress.com

Machining Hub Adapters with Keyways for Wheelchair Motors

This post describes how to custom build the hub adapters with keyways for wheelchair motors.

We will be making 4 of these adapters which will fit on top of the 6″ Rims through nuts and bolts.

Equipment:

Baxter Verticut 14″ Horizontal Bandsaw	Technical Support Center, University of Windsor, Ontario
Harrison M300 Horizontal Lathe (13″ x 40″)	Technical Support Center, University of Windsor, Ontario
Charmilles’ Robofil 240SL Electrical Discharge Machine (EDM)	MAME Laboratory, University of Windsor, Ontario
Dewalt Drill	Technical Support Center, University of Windsor, Ontario

Materials Required:

Mild steel, 4.5″x16″ (Cost: CAD $84.75)	Essex Metals, Oldcastle, Ontario
S-500 Coolant	Technical Support Center, University of Windsor, Ontario
Magic Cutting Fluid (oil)	Technical Support Center, University of Windsor, Ontario

Steps

1. Cut the steel tube into 4 equal parts using the Bandsaw and mount the first piece on the Lathe for machining.
   

   Mounted Steel for Machining (Front View)

   Mounted Steel for Machining (Side View)

2. Set the readout to zero and keep cutting into the stock by turning until you get a length of three inches.
   
3. Chamfer the edges of the bottom side with a 45 degree angle, so that it can fit the center of the rim tightly.
   
4. Drill a small hole in the center of the bottom plate.
   
5. Drill a bigger hole now, while using the S-500 coolant.
   
6. Apply some cutting fluid to the reamer and cut out the exact 17mm hole size in the bottom plate.
   
7. Chamfer the edges of the hole with a 45 degree angle, using a Dewalt drill.
   
8. Drill three holes in the triangular pattern into the bottom plate.
   
9. Place the part into the EDM machine and set it up for cutting the keyway. Once firmly installed, feed in the program and fill up the tank with de-ionized distilled water, and let the wire cut the keyway.