Barrett Technology: Liquid Cooled Motor

One of the few companies I've been at that didn't make me sign a strict NDA and encouraged me to share my most interesting work was Barrett. One of the projects I'm most proud of from working with them was the design and build of a liquid cooled motor. I created models and drawings in Solidworks, paying close attention to the tolerances involved and had parts sent out to a shop to be built. Follow the break for a step-by-step process to build one of my motors.

Building A Liquid Cooled Motor

Step 01 Choose your adhesives carefully. This one was designed to be thermally conductive, but as you can see here, it can also support 200lbs per square inch (psi) in shear. This is overkill for a motor only capable of creating 12psi but at least it won't break for a very long time.
Step 02 Get all the supplies needed to adhere the stator to the case. You'll need one half cooling block, the stator, a small disposable mixing dish, something to mix with, isopropyl alcohol, and your selected adhesive.
Step 03 Clean off all bonding surfaces and be sure not to touch them afterwards, your finger oils can decrease the strength of the bond.
Step 04 Mix your epoxy. A cartridge gun is almost required to make this at all easy. A mixing nozzle is a bonus but it'll waste whatever epoxy is left in the nozzle when you're done.

Step 05 Coat one mounting surface evenly. Luckily this stuff is viscous enough that it doesn't run.
Step 06 Seat the stator into the case. The stator will seat against an edge on the inside of the case to center itself properly.
Step 07 Be sure the cables are centered on the case so that they will easily route to their exit.
Step 07B Cure the adhesive used as directed. The epoxy I used wants to be cured at 60C for 3 hours.

Step 08 Cure the adhesive used as directed. The epoxy I used wants to be cured at 60C for 3 hours.
Step 09 Gather materials to adhere bearings into the endplates of the motors. You'll need two bearings and two endplates per motor, isopropyl alcohol, Loctite 7471 Primer, and Loctite 680.
Step 10 Clean the adhering surfaces with isopropyl alcohol to remove oils and prime with the 7471. Again, be sure not to touch the mounting surfaces.
Step 11 Apply a small amount of Loctite 680 to the end plate bonding surface. This is a thin adhesive and pooling is natural but should be avoided if possible.

Step 12 Seat the bearings as shown and cure at 100C for an hour.
Step 13 Gather the materials needed to construct the motor shaft. You'll need the rotor, drive shaft, 2mm spacer bearing, retaining ring, and the materials from the previous step.
Step 14 Clip the retaining ring onto the motor shaft.
Step 15 Slide on one end plate as shown so that it rests on the retaining ring.

Step 16 Slide on the 2mm spacer so it rests on the bearing.
Step 17 Using a vice or file, texture the outside of the shaft to ensure a good Loctite 680 Bond as shown.
Step 17B This is about the right amount of texture.
Step 18 Do the same to the rotor's inner diameter with a pick or steel cutting blade.

Step 18B
Step 19 Clean both the driveshaft and rotor inner diameter with isopropyl alcohol.
Step 20 Prime both surfaces with Loctite 7471.
Step 21 Coat the inside of the rotor with a thin layer of Loctite 680.

Step 22 Press the rotor on as shown. This should put no pressure on the bearing.
Step 22B Stop when the rotor just barely touches the 2mm spacer.
Step 23 Clean off the shaft were the 680 covered rotor slid over and cure at 100C for an hour.
Step 24 Gather all materials needed to assemble the motor body. This includes The glued stator/case assembly from earlier, the middle separator plate, the second half cooling case, epoxy materials, and Loctite 518 gasketing compound.

Step 25 Clean all bonding surfaces with the isopropyl alcohol.
Step 26 Apply loctite 518 as shown in red on step 27 to the middle plate, and seat as shown. Press firmly to get a good, close seal.
Step 27 Clean all mounting surfaces thoroughly including the case faces, stator OD, and case ID. Mix epoxy and apply to bonding surface as shown, and apply Loctite 518 to bonding surface as shown.
Step 28 Seat the two components firmly to get a good seal. Try not to spin the case in relation to the rotor as the case parts meet to get a good 518 seal.

Step 28B Be sure the Stator wires exit the assembly as shown.
Step 29 Clamp the Stator Case assembly tightly with a rubber-footed clamp to remove any excess Loctite 518 and prevent damage.
Step 30 Cure in the oven at 60C for three hours.
Step 31 Clean the stator case back face and apply Loctite 518 as shown.

Step 32B Route the wire carefully to look like this.
Step 33 Seat the unused back plate in the case and pull the stator wires all the way through as shown.
Step 34 Apply the Loctite 518 to the front of the stator case and the backplate with the bonded rotor shaft as earlier and seat the parts together. WARNING: The magnets in the rotor are strong and will do their best to mess up any finely laid adhesive. Be extremely careful. Be sure the other end of the shaft protrudes from the rear back plate bearing.
Step 35 Clamp the entire assembly together with soft jaw clamps.

Step 36 Apply the retaining ring to the back of the shaft.
Step 37 Bolt assembly together using M4x60 bolts and nylock nuts and cure in the oven at 60C for three hours.
Step 38 Connect to your high powered, liquid cooled system and watch the awesome unfold.
Step32 Route wires from stator through the unused back plate, clean all mounting surfaces, and apply Loctite 518 as shown.

System 1 This water cooled case allows for 2 times the sustained power output of the motor with no risk of damage.
System 2 Run motor cooling paths in parallel, not series for even cooling.
System 3 This is overkill for just one system, but the guys at Barrett want to run 5 in parallel.
System 4 This is the motor hooked up to our high-powered steel cable fatigue tester, also designed and built by a team of three interns this summer. Though the motor case was purely my design, this project was a huge team effort.

System 5 For serious cooling, get a serious pump. This one is from McMaster and has 3 times the flow rate as pumps sold by PC liquid cooling companies and an equivalent price.
System 6 It creates turbulence and waves in the cooling reservoir.
System 7 Lighting may not be classy, but its certainly eye catching. Also, 9 fans on a radiator might be overkill but we really REALLY want this setup to run cool.

As you can see above, one of my major contributions was the design and prototyping of a liquid cooled version of their motor. This was a really fun piece to design and build as it really let me expand on areas I wasn't yet comfortable with, like liquid cooling and design for manufacturing, as well as explore whole new areas like purpose-selected adhesives and brushless CD motor performance analysis. I came away pleased with my work there, and Barrett seemed pleased as well, since they created more of our setup and my motor since I left. I hear they're planning on making four or five of our setup so they can have cables running all the time.