Motor Status - scottbez1/smartknob GitHub Wiki
Status of the Motor
This page is dedicated to get an overview about the Motors and their respective suitability for this Project mentioned in the Issue https://github.com/scottbez1/smartknob/issues/16.
Why is it hard to find a suitable motor?
The SmartKnob View requires a few motor properties that are tricky to find together:
- Low/zero cogging (completely smooth rotation when off) - This is the most important aspect and also hardest to find. The majority of cheap hobby BLDC motors (even one marketed as "gimbal" motors) have noticeable cogging, meaning the motors wants to snap to certain points when unpowered. Cogging torque must be extremely low for the SmartKnob so that the knob turns completely smoothly when no virtual detents are enabled, and to avoid the cogging torque "pulling" to an adjacent position when you let go of the knob. The original motor has essentially zero discernible cogging. Generally motors that use discrete neodymium
- High pole count and/or low "kv" - In order to get smooth/precise angle control, it's useful to have more poles. This generally goes hand-in-hand with a low "kv" value, and both generally mean that the motor was specifically designed for low-speed operation and will be less likely to overheat when driven at low speeds with no airflow. The original motor has 7 pole-pairs and a KV around ~270.
- Appropriate coil resistance - Somewhere around The SmartKnob is designed around 5V USB operation using a USB-C connector, allowing theoretically up to 3A (but the TMC6300 motor driver currently used is limited to 2A). This means the motors need to be high enough resistance to avoid drawing too much current. The original motor has a U-V resistance of ~8 ohms, which results in a nice balance of torque vs heat. The design could be changed to accommodate a different voltage/current if absolutely necessary (e.g. using USB PD for higher voltage, and changing to a different motor driver), but this would result in substantial redesign.
- Diametric encoder magnet - In order to read the angle of the knob (and provide closed-loop haptic feedback), the SmartKnob uses a magnetic encoder, so the rotor needs to have some kind of diametric magnetic field that the encoder can read. Combined with the hollow shaft, this generally means the motor needs a diametric magnetic ring affixed to the rotor (though one could likely be sourced separately if needed)
- Hollow shaft - If you don't want an LCD screen, you don't need a hollow shaft, but otherwise the hollow opening diameter needs to be large enough for the physical support column for the LCD + its power/data wires. On the original design, this is an ID of ~6mm, which is barely enough for a 3d-printed support column and the 8 wires (+clearance). A smaller hollow shaft could work, but would likely require substantial mechanical changes, such as using a thin-walled brass tube.
Reference
As mentioned in Post https://github.com/scottbez1/smartknob/issues/16#issuecomment-1080845501 here are the desired specs
- 32mm OD, 5.9mm ID
- 14 poles (7 pole-pairs)
- 12 slots
- U-V coil resistance of ~8 ohms
- essentially zero cogging torque (this is a very rare attribute from testing a bunch of small "gimbal" motors)
- according to original product listing, 3280RPM at 12V, or 273KV (this is untested, but does match the expectation for a gimbal motor to have a low KV rating)
List of used abbreviation
| Abbreviation | Description |
|---|---|
| ID | Inner Diameter |
| BLDC | Brushless Direct Current (Motor) |
Current status
(updated 2022-06-26)
There are 2 promising options:
- Wanzhida OT-EM3215BLDC - this appears to be the original motor manufacturer, and I have received samples and sent an original motor to them to confirm production parameters. This is the most promising option.
- JD-Power MY-3515C - this is a really well-built motor (higher build quality than the Wanzhida motor). This has the 2nd least cogging torque of all motor options I've tested (2nd only to the original/OT-EM3215BLDC), so it's still a possible option. Mechanically, the knob would need to be made ~5-10mm taller to fit this motor, and the PCB would need a redesign of mounting holes for it.
I am also currently in talks with a US electronics manufacturer/retailer about possibly distributing motors once selected. More info to come!
Overview
lastest post checked 20.07.2022 https://github.com/scottbez1/smartknob/issues/16#issuecomment-1189671077
| Last updated | Photo | Status | Motor Name | Mentions | Note | Motor |
|---|---|---|---|---|---|---|
 |
Out of Stock | Micro Mini 32mm Hollow Shaft Brushless Ptz Motor Aperture 6mm | Original motor | Link | ||
| 14.03.2022 |  |
Out of Stock | 12V 3215 272KV | Link | Link | |
| 06.04.2022 | Not investigated | Cubemars | Link; Link | little cogging | Link | |
| 27.03.2022 |  |
Out of Stock/Not Suitable | Micro 3413 Modell | Link | Looks similar to original, but different size and hole pattern | Link |
| 27.03.2022 |  |
Not Suitable | standard t-motor GB2208 | Link | probably too thick | standard t-motor GB2208 |
| 20.07.2022 |  |
Not Suitable | MiTooT/Flycat/whatEverRandomName 2805 motors | Link; Link | noticable Cogging | Link |
| 27.03.2022 |  |
Not investigated | 2204 260KV / 2804 100KV / 2805 140KV Gimbal motor | Link | "Lidar" motor" Link | |
| 28.03.2022 | Not Suitable | 2804 140KV Brushless Gimbal Motor | Link | too much cogging torque, poor internal construction | ||
| 14.04.2022 |  |
Not Suitable | DC 20V-24V NdFeB PTZ Motor | Link; Link; Link; Link; Link | too much cogging torque | Link |
| 12.05.2022 |  |
Not Suitable | Flashhobby BGM2606-90T | Link; Link | too much cogging | Link |
| 30.03.2022 | Not investigated | GBM2804H-100T | Link | GBM2804H-100T | ||
| 30.03.2022 | Not investigated | - | Link | Link | ||
| 30.03.2022 | wait for sample pricing | GBM2606 | Link | smaller ID | ||
| 30.03.2022 | wait for sample pricing | GBM2608 | Link | taller | ||
| 01.04.2022 | might be unsuitable | Using HDD BLDC | Link; Link; Link; Link | need to modify shaft, usually low torque | ||
| 31.03.2022 | Not relevant | - | Link; Link | not relevant Link, likely the same seller of original Motor or a Reseller | Link | |
| 05.04.2022 | Sample order placed | jdpowersky DC-3514C | Link; Link; Link | Vendor replied already | Link OR Alibaba Link OR Link | |
| 05.04.2022 | Sample order placed | jdpowersky DC-3518C | Link; Link; Link | Vendor replied already | Link OR Link | |
| 01.04.2022 | Investigating | PM3505 with encoder | Link; Link | Currently investigating | Link | |
| 01.04.2022 | Investigating | GBM2804R 2804 Gimbal Motor | Link | Power Motor GBM2804R 2804 Gimbal Motor with Aluminum case /Slipring /AS5048A Magnetic Encoder for camera stabilizer | ||
| 02.04.2022 | Not investigated | - | Link | customizable in Bulk | Link | |
| 20.04.2022 | Not Suitable | thin gap frameless BLDC | Link; Link; Link | price per unit 1455 $, handmade | Link | |
| 04.04.2022 | may not be in Stock for long | 32mm diameter BLDC | Link; Link; Link; Link | can't be opened without damage, may deplete fast | Link | |
| 03.04.2022 | Ordered, waiting for arrival | - | Link | Link | ||
| 04.04.2022 | Not investigated | CD drive Motor | Link | Link | ||
| 05.04.2022 | Make to order | 32mm diameter with hollow Shaft | Link | Link | ||
| 06.04.2022 | Requested seller | 12V Hollow Shaft Brushless Gimbal 3215 with Slip Ring | Link | Link | ||
| 07.04.2022 | Not Suitable | HONGYI Micro PTZ Gimbal Motor 2204 | Link; Link | not enough power | Link | |
| 07.04.2022 | Not investigated | Frameless Motors | Link; Link | need a bearing assembly, pobably too expensive | Link | |
| 13.07.2022 | still investigating | Wanzhida OT-EM3215BLDC | Link; Link; Link; Link; Link ;Link; Link | issue with static friction | Link | |
| 04.05.2022 | tested | JD Power DC-3515C | Link; Link; Link; Link | pricey, higher torque but also more cogging | ||
| 14.04.2022 | Not Suitable | GM4008H | Link | cogging | ||
| 14.04.2022 | Not Suitable | 20V-24V 2804 PTZ BLDC Motor NdFeB | Link; Link; | prob. Cogging, no diametric magnet | Link | |
| 21.04.2022 | Not Suitable | PCB Stator | Link; Link ; Link | low torque | Link | |
| 03.05.2022 | Not Suitable | 3215 Motor see post | Link | too expensive | From Johaan1314 see post | |
| 08.05.2022 | Not investigated | Mini PTZ 12V 3215 272KV | Link | Link | ||
| 10.05.2022 | Not investigated | - | Link | Link | ||
| 24.06.2022 | Not Suitable | DC 20V-24V 2804 PTZ BLDC | Link; Link;Link; Link | not smooth | Link | |
| 17.05.2022 | Not Suitable | 32mm diameter Motor with limiter | Link | has limiter, can't be removed | ||
| 17.05.2022 | probably not suitable | 34,5mm BLDC with limiter | Link | has limiter | ||
| 18.05.2022 | Not investigated | 260KV BLDC 2204 | Link; Link | not cheap | Link; Link | |
| 28.05.2022 | Not investigated | Yuneec 2715 180 KV BLDC NdFeB | Link | Link | ||
| 28.05.2022 | Not investigated | GB2204 | Link | Link | ||
| 30.05.2022 | Not investigated | GB2208 | Link | |||
| 30.05.2022 | Not investigated | GB36-1; TMC6300 | Link | |||
| 30.05.2022 | Not investigated | GL30 | Link | |||
| 13.06.2022 | Ordered | Mitsumi 12V BLDC | Link | Link | ||
| 23.06.2022 | Not investigated | 32mm BLDC 3205 | Link | |||
| 23.06.2022 | -1000x1000.jpg) |
Not investigated | iPower GM3506 with AS5048A Encoder | Link | can be found without the encoder for cheaper | Link; Link |
| 02.07.2022 | Not investigated | Micro PTZ Motor DC12V 3205 | Link | Link | ||
| 06.07.2022 | Not investigated | Gimbal Motor 2204 260KV | Link | Link | ||
Other options
PCB Motor
Such as designed by Carl Bugeja
Viability
- Can this type of motor provide enough torque within the power requirements? There is some debate, but it's worth experimenting
3D Printed motor: brushless
Examples
Viability
- Can this type of motor provide enough torque within the power requirements? This is an open question
- "motors require laminations and not just solid blocks of metal" (Link to comment) (Refers to the viability of using 3D-printed metal parts). This is an open question
Design constraints
- The material used has to be able to handle some heat without deforming: "Windings get warm even when just in lower percentage duty cycle." (C44Supra)
Drawbacks
- No current designs that fit the smartknob. May have to be designed from scratch with multiple iterations requiring testing
- Limiting the printing to non-ferrous materials might limit the available torque
- Users would have to wind the coils themselves which is time-consuming and tedious
- Sourcing magnets might be difficult as there may be tight requirements for material, shape, and weight
3D Printed motor: other
Add any potentially viable options here