In this instructable, we will show you how to construct a desktop dynamometer like the one above.

Materials:

1 Anaheim Automation BLWS232D-36V-4000-12AE motor
- 4 Black-Oxide Class 12.9 Socket Head Cap Screws (Alloy Steel, M5 Thread, 20MM Length, 0.8MM Pitch)
- 4 Zinc-Plated Steel Flat Washers (M5 Screw Size, 5.3MM ID, 10.0MM OD)
- 4 Zinc-Plated Class 8 Steel Nylon-Insert Locknuts (M5X0.8 Thread Size, 8MM Wide, 5MM High)
1 Anaheim Automation BLY173D-24V-4000 motor
- 4 Low-Profile Socket Head Cap Screws (Class 8.8 Steel, M3 Size, 10MM Length, 0.5MM Pitch)
- 4 Type 18-8 Stainless Steel Flat Washers (M3 Screw Size, 3.2MM ID, 7.0MM OD)

6 Nonmarring Flat Point Set Screws (Type 316 Stainless Steel, M5 Size, 10 MM Long, 0.8 MM Pitch)
6 Class 04 Steel Thin Hex Nuts (DIN 439B, Zinc Plated, M5X0.8 Thread Size, 8MM WD, 2.7 MM HT)
Couplings:
- 1 OD12/19-AT Oldham Coupling Disk, OD 3/4" or 19.1MM, Black Acetal
- 1 MOCT19-5-A Oldham Coupling Hub, Clamp Style, Bore 5MM, OD 19.1MM, OAL 25.4MM, Black Anodized Aluminum
- 1 OCT12-4-A Oldham Coupling Hub, Clamp Style, Bore 0.25", OD 3/4", OAL 1", Black Anodized Aluminum
1.5 feet of 0.5" radius copper pipe

Tools:

3-D printer access
Tube cutter (we used Superior Tool 35078 7/8" O.D. Mini Tubing Cutter-Seven Eighths Outside Diameter Tube Cutter)
2, 2.5, and 4MM Allen wrenches (we used Eklind 21171 Fold-Up Set #M17, 1.5mm to 6mm Hex Keys)
8MM open wrench (or an adjustable wrench or pliers)

Step 1: Print the Body

Print out the two triangular fixtures and six tube ends by using the files located at this link.

Within that link, make sure to pick the correct triangular fixture for your motor dimensions, as there are four slightly different designs posted. The two designs for the motors used in this instructable are LMP-NEMA17-22-31-M3 and LMP-NEMA23-38.1-47.2-M5, so print just one of each.

Don't know what Plexim is? Click here to find out!

Step 2: Insert the Set Screws

Once your printer does its job, you should have a small hole on the side of each cylinder located at the triangular fixture's corners. These holes are designed to hold the hex nuts with flat point set screws which will be used to lock the fixtures' position along the copper pipes.

Upon inserting the M5 set screws into their nuts, use your fingers (if that doesn't work, use something like the back of a pencil or a screwdriver) to press the created pairs into the holes from the inside part of the cylinders, as shown. Make sure the end of the set screws peeking out on the outside of the cylinders is the end with the Allen wrench-accessible hole. Slightly twist out the set screw to make its inside end flush with the inside surface of the cylinder - this way you won't have trouble inserting the pipes later.

Step 3: Attach the First Motor

Use the four M5 socket head cap screws, washers and nuts to attach the BLWS232 motor. The washers and bolt heads should be on the side with the Plexim logo, and the nuts on the motor's side of the triangular fixture, as shown.

We suggest using an open (or an adjustable) wrench to hold the nut on one side while using the Allen wrench (number 4) on the other side to screw the bolt into the nylon-insert nut. This will take more hand strength and effort than you might expect: the nuts are intentionally very snug with the bolts to prevent the motor from becoming loose in the future, so hold those wrenches (or squeeze those pliers) tight!

Step 4: Attach the Second Motor

Use the four M3 socket head cap screws and washers (no nuts this time) to attach the second motor to the other triangular fixture. Again, the washers are on the side with the logo. You will use the Allen wrench number 2 for this.

Step 5: Cut and Insert the Pipes

Use a tube cutter to cut the copper tubes/pipes. You will need three pipes of the same length - the ones shown are 11 inches each, but you can go with 12 if you're into even numbers.

Insert the three cut pipes through both of the triangular fixtures (motor shafts facing inward), and add the circular, 3-D printed pipe ends, as shown.

Step 6: Connect the Motors!

You should have two couplings of different diameters which connect with a plastic disc. That disc serves as protection - if one of the motors were to lock during running, this piece would break, disconnecting the shafts and protecting the other motor from damage.

Slide the two motor shafts into the respective diameter holes of the coupling and tighten the coupling screws with an Allen wrench number 2.

Remember those set screws in the corners of the triangular fixtures? You may now fasten those with an Allen wrench number 2.5. Just be careful not to overtighten as that may bend your pipe, as shown in the picture above.