CamRoller Mini

I was so pleased with how my little CamRoller build came out a couple of weeks ago, that I decided I wanted to make him a little brother.

I designed the original to be capable of supporting my full frame camera with a decently chunky lens on it.

And I won’t lie, I was pleasantly surprised that it does so quite well! I didn’t even intend to put that big cinema lens on it, but decided to give it a shot. Even that big boy didn’t get the CG outside of the wheelbase….noice.

Unfortunately, that’s because that wheelbase is 200mm wide. Not as bad as an electric Hummer, but still pretty large on the work table. So I decided to make a ~50% scaled version, targeted at action cameras and/or cell phones.

And isn’t it adorable??

I think the 50% scaling really worked out nicely in terms of proportionality to an action camera form factor.

Interested in building one yourself? <<Grab the files here on Printables>>. If you do, please share your Make so I can see how it came out!

Before I dive into the BOM details, let’s take a little look at what’s holding up the GoPro.

The actual interface to the camera is provided by an off-the-shelf action camera mount. That camera mount has a 1/4-20 female thread, and it is actually part of the structure of the roller.

I designed it for a 1/4-20 x 3/4” flathead fastener. But I didn’t have any flatheads on hand, so I ended up going with a button head…nobody’s gonna see it under there anyway \(ツ)/ . It’s not ideal having the button head making just a line contact with the chamfer intended for the flathead, but I figure there’s enough meat there, it’ll be fiiiinnneeee.

That 1/4-20 fastener is clamping together the main bearing, and primary structure of the roller.

That structure comes from three components, Rot_top, Rot_center, and Rot_bot (I got it wrong in the image and was too lazy to export a new one…forgive me? :) ). These parts include v-grooves around their perimeters that serve as the bearing races to allow the roller to steer. Filling in those bearing races are a whole bunch-o-BBs.

The 1/4-20 fastener preloads this bearing together. When assembled, Rot_top and Rot_bot are rigidly fixed to each other, which allows for the gear on Rot_bot to provide the turning for Rot_top.

The driver for that motion lives on Rot_center, in the form of the worm and it’s thumb-friendly adjustment knob.

To hold the worm in place, and provide both radial and thrust bearings on both sides, are jewel bearings.

While I’ve done a few designs that use these integrated worm gears, this is my first time trying this ‘moving jewel bearing’ concept. What I mean by that, is the bearing on the right side of the worm, with the blue part opposite the worm, is fastened into place with a couple of M3s.

I added the tapered interface at the base, along with an intention offset in the fasteners locations in the nominal design, to drive an axial preload into the worm as the fasteners are tightened. The downside of this is that it does make it a little less straightforward to put in the heatsets, but it’s very doable.

To keep track of where that worm has put the steering, there are markings on top of Rot_top, and a corresponding pointer on Rot_center. The minor ticks are at 5 degrees, and the major ticks are at 15 degrees.

Curious what that angle means in terms of turning radius? Well, I took a stab at modeling it, and here’s the plot I got for the Turning Radius (in millimeters) vs. the Steering Angle (in degrees).

I did a crude spot check at 10, 15, 30, and 45 degrees, and here is what I found:

• 10deg - 590mm

• 15deg - 390mm

• 30deg - 205mm

• 45deg - 175mm

Sooooo, yeah, I seem to have had a 2x error somewhere in my math :) But I tend to just dial it in by look anyway, so I’ll look for that later.

I took these measurements by strapping a laser pointer to the top of my camera, and then watching how the dot moves on a ‘wall’ at a measured distance away. You can see my super sophisticated setup below…and yes, yes that IS a cat toy laser pointer :)

This actually worked quite well for getting my radius measurements, but it did point out an overall flaw with both of my little CamRoller designs. Because the camera mount (either the ball head on the big boy or the action cam mount on the mini) is fixed to its Rot_top, it rotates along with Rot_top. But, to maintain the camera pointing toward the center of rotation, it needs to rotation half of the distance.

As a result of this, the further you go in the steering angle, the more of an eccentricity is introduced. I hadn’t noticed it with CamRoller, because I was cancelling this out with the ball head without noticing. Because I have a fixed action camera mount on the mini, it doesn’t have that degree of freedom.

Replacing the action cam mount with a small ball head, or possibly with an action cam adapter, this could be handled easily enough. But I have to admit, I now kind of want to think about how I could cancel this out 🤔

But anywho.

Oh, right, I forgot to talk about where the TPU hits the table. For the wheels, I went with a multi-material print of a PETG hub, surrounded by a TPU ‘tire’.

The TPU is staked into the PETG hub, and I left a 0.10mm nominal gap, which worked well for getting my parts to print, and hold together, well. Sitting inside that hub is a 10x15x4mm roller bearing and a retainer cap that sandwiches the bearing against the main body. And inside the main body (either Rot_top or Rot_center) is an M3 heat set to tighten that wheel into place.

One unfortunate aspect of this configuration is that I’m relying on a tight fit on the wheel hub to the outer bearing race. To dial this in, I printed the hub alone a couple of times to get the fit I wanted.

I think that pretty much covers how it works. Here’s what’s in it.

I lied…I realized after writing all of the above that there was a small improvement I should include before publishing the models. I added a 2mm dowel pin between Rot_top and Rot_bot to make clocking during assembly easier.

Ok, NOW that covers how it works, here’s the full list of what’s in it.

BOM

Printed Parts:

• (1) Rot_bot (PLA)

• (1) Rot_center (PLA)

• (1) Rot_top** (PLA)

• (4) WheelRetainer (PETG)

• (1) Worm (PETG)

• (1) WormRetainer (PLA)

• (4) Wheel_hub* (PETG)

• (2) Wheel_tireA* (TPU)

• (2) Wheel_tireB* (TPU)

Off-The-Shelf

• (1) Action camera mount with 1/4-20 interface

• (1) 1/4”-20 x 3/4” flathead (or similar :) )

• (2) 9.5mm steel balls (I use 3/8” slingshot ammo) - Worm bearings

• (68) 4.5mm steel balls (aka BBs) - Main bearing

• (2) M3x18mm flathead - For worm hold down

• (4) M3x6mm heat set inserts - For wheel attach

• (2) M3x4 heat set inserts - For Worm retainer

• (4) 10x15x4 Roller bearings (6700-2RS) - Wheel bearings

• (1) 2 x 8 mm dowel pin - For Rot_top to Rot_bot clocking

• The wheels were printed as sub-assemblies from sub_WheelA.step and sub_WheelB.step

** I printed versions of Rot_top both with, and without a material in the -45, 0, and 45 deg lettering. For with lettering, I printed it from the Rot_top_dualcolor.step file

The Parts

Rot_top

Rot_center

Rot_bot

Da Worm (aka Worm)

WormRetainer

WheelA

WheelB