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How to install a Frameless Torque Motor in a system?

by robert•

Hey folks, thanks for hanging out here – I’m the guy who’s been hooking up frameless torque motors to all kinds of systems for the past 8 years, and let me tell you, installing these bad boys isn’t rocket science… but skip a step, and you’ll end up with weird, wobbly performance that makes your whole setup throw a fit. A lot of folks reach out to me confused, like “Wait, I just slide it in, right?” Nah, trust me – these motors are designed to be low-profile, super high-torque workhorses, and cutting corners on install will cost you way more time and cash later. Frameless Torque Motor

First, let’s get one thing straight: frameless torque motors aren’t your off-the-shelf NEMA 23 motor you used for your old conveyor. They’re split into two parts: the stator (that’s the stationary coil side) and the rotor (the rotating magnet side). Unlike standard motors that bolt into a housing, these basically slot right into your existing gearbox or axis shaft – that’s why they’re called frameless. But that “simple” design also means you’ve got to nail every alignment step. I’ve seen first-timers misalign the rotor by just 0.2mm and end up with 15% less torque, plus weird cogging noise every time it spins past 90 degrees. Not cool.

Let’s break this down step by step, like I’m walking you through my shop floor. No jargon overload, I promise – just what I actually tell my customers when they drop their motors off for install.

Step 1: Prep Your Workspace & Parts First (Don’t Skip This)

I know, your shop’s already swamped with parts, but if you install a motor on a dirty workbench? You’ll get a metal shavings stuck on the stator coils, and that’s a one-way ticket to fried windings. Here’s what you’ll need:

  • Your frameless torque motor (obviously – make sure you’ve got the right size: stator outer diameter, rotor inner diameter, and torque rating matched to your axis. If you’re not sure, shoot me a note before you even unbox it – I’ve seen people grab a 10Nm motor when they needed 25Nm, oops.)
  • The axis shaft you’re mating it to (make sure it’s clean, no burrs – a file or sandpaper on the high spots takes 2 minutes)
  • Alignment tools: a dial indicator (not a tape measure, that’s for home projects), a precision torque wrench, a set of feeler gauges
  • Isopropyl alcohol and lint-free cloths (no paper towels, they leave lint)
  • Loctite 243 (medium strength, not 603 – that’s permanent, you’ll never get the rotor off if you mess up)
  • A clean, flat work surface – I use a granite surface plate because it’s perfectly flat, but a thick aluminum plate works too.

Pro tip: When you unbox the motor, don’t touch the stator coils or rotor magnets with your bare hands. The oils from your skin can corrode the coils, and if you get skin on the magnets? They’ll hold tiny metal shavings forever. I always wear nitrile gloves for this part.

Step 2: Fit the Rotor to Your Shaft – This Is Where Most Mess Ups Happen

The rotor’s inner bore has a keyway (usually) to lock it to the shaft, right? First, slide the rotor onto the shaft. Don’t force it – if it sticks, check for burrs on the shaft keyway or the rotor’s inner bore. You should be able to slide it on by hand (or with a rubber mallet, wrapped in a cloth so you don’t dent the magnets) until it’s flush with the shoulder of the shaft.

Now, torque the setscrews (or the locking hub, if you’ve got a high-torque model) to the spec I give you. No guessing here – use that torque wrench I mentioned. If you under-torque, the rotor will slip when you crank up the motor’s power, which will strip your axis’s gears or even break the shaft. If you over-torque, you’ll crack the rotor’s magnetic ring – I’ve had a customer do that once, and he had to wait 3 days for a replacement motor because he thought “more torque = better.” Spoiler: It doesn’t.

Here’s a quick check: After you torque the setscrews, grab the rotor and try to wiggle it side to side. If there’s any play? You messed up. Loosen the screws, clean the bore and shaft again, and try it again. That play will turn into wobble once the motor’s running, and your camera axis (or whatever you’re using this for) will have blurry footage. No one wants blurry footage.

Step 3: Align the Stator to the Rotor – The Make-or-Break Step

This is the big one. The stator is stationary, so it mounts to your machine’s housing, and it needs to be perfectly concentric with the rotor. If they’re out of alignment, you get uneven air gap – that’s the space between the stator coils and rotor magnets. Too little gap, and they’ll rub; too big, and you lose torque. For most frameless motors, we spec an air gap of 0.5mm to 1mm, depending on size, but the alignment’s way more important than just hitting that number.

How to do this right:

  1. Mount the stator to your housing – don’t tighten the bolts all the way yet. Leave them finger-tight so you can shift the stator a little.
  2. Slide the rotor onto the shaft (it should spin smoothly now) and set up your dial indicator against the outer edge of the stator. The indicator’s probe should be touching straight out, perpendicular to the shaft.
  3. Spin the rotor 360 degrees. You want the dial indicator’s reading to stay within 0.02mm of the same number – that’s perfect concentricity. If it jumps more than that, shift the stator left or right until it’s spot on.
  4. Once it’s aligned, tighten the stator bolts in a crisscross pattern (like you’re tightening a wheel on a car) to keep everything even. Don’t tighten one all the way before the others – that’ll tilt the stator.
  5. Double-check the gap after tightening. Spin the rotor again, make sure the indicator reading didn’t shift. If it did, loosen the bolts and adjust again.

I’ve had customers skip this alignment step before, and they come back a week later complaining their motor is loud and only makes 70% of the rated torque. 9 times out of 10, it’s just a 0.1mm misalignment. It takes 10 extra minutes, don’t skip it.

Step 4: Wire the Motor & Test the Air Gap – Don’t Skip the Post-Install Check

Wiring a frameless motor is straightforward, but again, follow the pinout we give you. Most of our motors are three-phase (U, V, W), plus hall sensors for commutation. Don’t mix up the phases – if you wire U to V and V to U, the motor will spin backward, and you’ll have to re-calibrate your whole system. Label each wire with tape so you don’t forget which is which.

Once it’s wired, here’s a quick test I always do before powering it up: Grab a feeler gauge and slide it between the stator and rotor at 4 spots around the circle. You should get the same gap at every spot, within 0.05mm. If one spot feels tighter, that’s still a misalignment – stop, adjust, don’t power it on. If you power it on with a rub, you’ll scratch the magnets, which will ruin the motor’s performance long-term.

Step 5: Mount the Feedback Device (Encoder/Resolver) – Yes, Even If You Think You Don’t Need It

A lot of folks think, “This motor’s torque is high enough, I don’t need an encoder.” Nah. Frameless motors are often used for precision applications – like robotic arms, CNC machines, or medical imaging equipment – and you need feedback to control speed and position. When you add an encoder, you mount it to the opposite end of the shaft from the rotor, or sometimes between the rotor and your axis.

Pro tip: Align the encoder the same way you aligned the motor – use a dial indicator to get concentricity. If the encoder’s misaligned, your system’s position will drift over time, even if the motor itself is fine. I once fixed a CNC mill that was cutting 0.5mm too big every part, and it was just a misaligned encoder. The customer thought the motor was bad, nope – just a $50 alignment fix.

Common Mistakes I See All the Time

Let’s talk about the stuff that trips up even experienced folks:

  1. Not accounting for thermal expansion: If your system runs hot, the shaft and housing will expand, which can reduce the air gap. I always tell customers to check the gap after the motor has been running for 15 minutes at full speed, then adjust if needed.
  2. Using the wrong fasteners: Don’t use random bolts from your toolbox – make sure the bolts for the stator are the right length and thread size, and use flat washers to spread the load. Too small a bolt, and it’ll strip the housing; too long, and it’ll hit the rotor.
  3. Ignoring cable management: The motor’s wires shouldn’t be pulling tight when the shaft spins. I’ve had a customer’s motor seize up because the wire got caught between the stator and a bolt. Leave a little slack, and secure the wires so they don’t move.

Now, before I wrap this up, I want to say: This isn’t a one-size-fits-all guide. Every system’s different, so if you’re not sure about any step – whether it’s sizing the motor, alignment, or wiring – hit me up. I’m not the type to hide behind a manual; I actually work with these motors every day, so I can give you real advice, not just what the spec sheet says.

Robot Joints If you’re looking to upgrade your system with a frameless torque motor, or just have questions about what size you need, get in touch. We’ve got motors for everything from small medical robots to heavy industrial axes, and we’ll work with you to make sure it installs right the first time, no headaches.

References

  1. Frameless Torque Motors: Installation Best Practices. Motion Control Association, 2022.
  2. Precision Alignment Guidelines for Direct Drive Motors. Mechanical Systems Design Journal, 2021.
  3. Thermal Management for Brushless Frameless Motors. IEEE Transactions on Industrial Electronics, 2020.

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