Main Site Documentation

Looking for small low cost slew ring


#1

I have a home project that requires a top and bottom section to rotate around smoothly. I will use a heavy duty servo driving a toothed wheel much like a slew ring on a crane base to rotate the base. It does not turn more than 360 degrees max so no continuous rotation.

To make sure the movement is smooth I need to find a slew ring with ball or roller bearings. Max diameter would be 120mm

Anyone seen such a thing?


#2

Hi Dave, I would go for https://www.sparkfun.com/categories/258 and find a clamp and a bearing that could rotate smoothly, and then add then add a gear to the shaft, and then add a gerar to your motor. You might go for two rubber wheels (one on shaft one on motor) to move the shaft for some flexible coupling?

Are you building an automatic rotating cheese board? :whistle:


#3

They are a bit on the small side.

I am going to try and make my own Jibo type device with a Raspberry Pi 3, 7" LCD and some 3D printed parts. Just for the fun of it. :slight_smile:


#4

@ Dave McLaughlin - i made my own for this.


The gears rest on a 3d printed thrust bearing using some really cheap 4.5mm bb ammo in a 3d printed cage.


#5

@ hagster - That looks really great. Good work.


#6

Nicely done. If I could like it twice, I would.


#7

That is really impressive!


#8

@ hagster - Very Mint :clap:


#9

@ hagster that looks nicely done.

Looking at your slew ring, how to you retain the 2 parts together? I assume there is a central shaft that clamps them together?

This is the design I am working on. I am still working on the method of rotation. I plan to use small DC motors to rotate the upper and lower parts which will allow angular changes. Stepper motors are too noisy for this.

As I don’t have a 3D printer I will use Shapeways to make the parts. Probably going to be around $600 for all the parts.


#10

You should check out the TMC2660 drivers. I’m using them on my printers now (via Duet WiFi controllers). They’re impossibly quiet compared to all the others I’ve used before. The only noise I can hear from my printers now are the fans.


#11

@ Dave McLaughlin - yes there is a central shaft that holds it in place horizontally, but the v-groove tracks actually do a lot of that job. Vertically gravity that keeps it in place, but also the herringbone gears hold it down too. I may add some sort of top bearing that clamps it down at some point too.

In my case most of the noise comes from the coupling to the table. That book its placed on in the video is actually to reduce that. I bet NEMA14 pancake steppers would be quiter than these beefy NEMA17 or you could use the 28byj-48 geared mini steppers are pretty quiete IIRC, but if you dont need absolute accuracy then servo motors are likely the best choice as these give some positional control too.

Thats a lot of money to spend with shapeways. If I were you I would get yourself a cheap 3D printer. That gives you far more opportunity to itterate on your project. With shapeways you tend to want it to be right first time(unless you are a CAD god it wont be).


#12

Forgot to say. The herringbone gears are much quieter than the straight cut ones too.

Also, thanks for all the kind words about my pan tilt(@ justin,@ terrence,@ mcalsyn,@ rockybooth). I will make a detailed write up(with speed, accuracy, backlash and load tests etc) at some point, but i still have lots of stuff to do one it.

What i really need is a cool name for it if anyone has any ideas? PannyMcTiltface?


#13

lol


#14

Regarding stepper noise, there is a type of DC gearmotor (whose correct name I can’t recall and could not successfully google this morning) that might do the trick. I’ve been wanting to give one a try.

The gearing on these motors are made of a ring gear and a flexible (stainless?) gear cup on the inside of that ring. Think of a spirograph - the inner cup has just a few less teeth than the outer ring. The motor drives a cam that slightly deforms or deflects the inner cup to make contact with the outer ring. The output is attached to the cup. The result is a very high reduction ratio, low noise, and zero-current shaft locking. The whole package tends to be pretty small too. I think these find use in space-qualified installations and high-end robotics.

Anyway, I always wanted to try out one of these, but now I can’t even remember the proper name for them. Do these gear motors sound familiar to anyone?


#15

@ mcalsyn - the harmonic drive


#16

Two other things I do on my printers that will almost completely eliminate this noise. First use stepper dampers between your motor and your bot. Second, put Sorbothane dampers between your bot and the table.

Here are some before and after videos I took a while back showing the difference with & without the stepper dampers. The difference is even better than that video recorded. Note that these were taken when I was using noisey DR8825 drivers. With the new TMC2660 drivers the difference would be even more dramatic.


#17

@ ianlee74 - noise level isnt really high up on my design priorities, but if I may look at those drivers if i do a new driver board. I have the DRV8825s at the moment.


#18

Noise does sound like it’s important to Dave, though. This was mostly aimed at him.


#19

Check this out. I was looking for something to calculate the gear ratios and get an idea of what the speeds look like with the different motor outputs.

Handy little website


#20

I’ve managed to complete the design to about 90% now with some tidying up and some support to add for the plastic parts.

The 2 DC motors are located in the middle body section as shown. They can rotate the unit 360 degrees. I made the change to this as I am planning to use 2 Adafruit type slip rings to allow this to be the case.

The RED board is where the audio amp and microphone pre-amps will be located along with the 2 motor drivers. Planning on using a NETMF device for this. G30 or G80 but not decided yet. The motors have encoders and the only thing I need to add to the design is on some zero point detection. Thinking I can just use a hole in each rotate part with an IR diode and IR LED looking through for this.

There is a Neopixel ring in the lower section and using a transparent or frosted material from Shapeways should make a nice light at the bottom for feedback.

The attached drawings are shown with transparent body parts to show the internal workings. The base is a chunk of stainless machined steel 20mm thick to give it some stability.

Appreciate any feedback or ideas I have missed out?