Windup Bunny 2 With a PLA Spring Motor and Floating Pinion Drive

Windup Bunny 2 is a dual floating pinion all wheel drive update to my original Windup Bunny of years ago. Even though Windup Bunny 2 is larger (1.5 times) and heavier (120 grams versus 64 grams) than the original Windup Bunny, it runs faster and further thanks to its dual floating pinion / rotating pinion gear carriage design along with a stronger spring.

I've designed rear wheel drive floating pinion models before that utilize both gravity and rotational momentum in order to disengage the rear axle from the spring motor once the spring motor energy is depleted. Windup Bunny 2 is more complicated in that it is all wheel drive thus both the rear and front axles must disengage from the spring motor in order to coast and / or function as a push / pull toy. In order to accomplish this, the design incorporates a rotating dual floating pinion carriage with a rear mass heavy enough to disengage both the front and rear axles from the spring motor once the spring motor energy is depleted.

Windup Bunny 2 is another favorite of our kids and grandkids, providing both a windup and push / pull toy for the older and younger family members. And while much sturdier than the original Windup Bunny, it does require patience and finesse to print, assemble and test.

As usual, I probably forgot a file or two or who knows what else, so if you have any questions, please do not hesitate to point them out as I do make mistakes in plenty.

Designed using Autodesk Fusion 360, sliced using Cura 3.5.0, and printed in PLA and Tough PLA on an Ultimaker 2+ Extended and an Ultimaker 3 Extended.

Step 1: Purchase, Print and Prepare the Parts.

I purchased four 31mm I/D by 3.5mm section O-Rings for the "tires".

Please refer to the file "Windup Bunny 2.pdf" for the parts count and settings.

Prior to assembly, I test fit and trimmed, filed, sanded, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. If you decide to make your own Windup Bunny 2, depending on the colors you chose, your printer model and your printer settings, more or less trimming, filing and/or sanding may be required. I carefully filed all edges that contacted the build plate to make absolutely certain that all build plate "ooze" was removed and that all edges were smooth, especially the gear teeth. I used small jewelers files and plenty of patience to perform this step. I also used 6mm by 1 right hand threaded taps and dies to prepare the threaded parts prior to assembly.

Step 2: Assemble the Floating Pinion Carriage.

I assembled the Floating Pinion Carriage as follows:

• Positioned "Gear, Idler, Front (8, 1.5).stl" and "Gear, Idler, Rear (8, 1.5).stl" onto "Carriage, Left.stl".
• Positioned "Carriage, Right.stl" onto the carriage assembly, then secured carriage right in place with two "Axle, Carriage.stl".
• Threaded "Bolt, Carriage.stl" into the assembly.

With the floating pinion carriage assembled, I made sure the pinions rotated freely in the carriage.

Step 3: Assemble the Frames.

To assemble the Frames, I performed the following steps:

• Positioned "Knob and Axle.stl" into "Frame, Left.stl".
• Pressed "Spring.stl" onto "Knob and Axle.stl" while positioning the spring end onto the spring mount in "Frame, Left.stl".
• Pressed "Pawl.stl" onto "Knob and Axle.stl".
• Positioned "Gear, Pawl (40, 1.5).stl" onto "Pawl.stl".
• Positioned "Gear, Compound ((8, 1.5), (40, 1.5)).stl into the carriage assembly.
• Slid the carriage assembly onto the frame assembly.
• Secured "Frame, Right.stl" onto the assembly using three "Bolt, Frame.stl".
• Secured "Frame, Left.stl" using three "Bolt, Frame.stl.

With the frames assembled, I made sure the spring motor functioned properly, and that the carriage assembly rotated freely.

Step 4: Add the Wheel Axles and Wheels.

To add the Wheel Axles and Wheels, I performed the following steps:

• Wrapped the four O-Rings on each of the four wheels.
• Pressed "Gear, Axle, Front (8, 1.5).stl" onto "Axle, Front.stl" exactly 21.20mm from one end of "Axle, Front.stl". If the gear was not tight on the axle, I used a small dot of cyanoacrylate glue to secure it in place.
• Pressed "Gear, Axle, Rear (8, 1.5).stl" onto "Axle, Rear.stl" exactly 25.20 mm from one end of "Axle, Rear.stl". If the gear was not tight on the axle, I used a small dot of cyanoacrylate glue to secure it in place.
• Positioned the front axle assembly between the left and right frames such that the gear aligns with "Gear, Idler, Front (8, 1.5).stl".
• Pressed one "Wheel, Front.stl" onto the front axle assembly, with the axle flush with the wheel outer surface.
• Pressed the remaining "Wheel, Front.stl" onto the axle assembly, 180 degrees out of phase from the first wheel, with the axle flush with the wheel outer surface.
• Positioned the rear axle assembly between the left and right frames such that the gear aligns with "Gear, Idler, Rear (8, 1.5).stl".
• Pressed one "Wheel, Rear.stl" onto the rear axle assembly, with the axle exactly 4mm proud of the wheel outer surface.
• Pressed the remaining "Wheel, Rear.stl" onto the rear axle assembly, with the axle exactly 4mm proud of the wheel outer surface.

With the wheel axles and wheels assembled, I made sure that both the front and rear axles rotated freely.

Step 5: Final Assembly.

I performed the following steps for Final Assembly:

• Positioned "Foot, Right.stl" onto the assembly and secured in place with one "Axle, Foot.stl" and one "Hub, Foot.stl".
• Positioned "Foot, Left.stl" onto the assembly and secured in place with the remaining "Axle, Foot.stl" and remaining "Hub, Foot.stl".

And that is how I printed and assembled Windup Bunny 2.

I hope you enjoy it!

Comments

[ToddK4]

I just printed one of your PLA Spring Motor 2's a week or so ago. It has provided several hours, I'd guess, of entertainment and proved to me that a PLA spring works. I believe when I get a chance to print the Bunny 2, it will entertain my little girl (probably me as well) quite well. I'll have to order some brighter color filament (I'm thinking pink and purple) -- she doesn't pay much attention to things printed in black or blue like I usually use.

Thanks for sharing your wonderful work!

[gzumwalt]

Hi ToddK4,

I'm glad you enjoyed the spring motor, I have two on my desk and they indeed make a great fidget toy and conversation piece. I hope you do print Bunny 2, my kids and grandkids enjoyed it and I bet your little girl will too.

And you are very welcome, I truly enjoy sharing as my goal is creating smiles!

Greg

[ToddK4]

Finally found the time to get this done. Little one managed to break one the feet almost immediately, but it won't take long to print another.

[gzumwalt]

Hi ToddK4,

Wonderful work, congratulations !

Greg

[nlkirchn]

I've printed and assembled the Windup Bunny and the problem I have encountered is the floating pinion while being very free binds with the front and rear wheel gear to the point that the spring cannot turn the wheels. Without the pinion engaged everything moves freely. Can you suggest a solution to this problem or why it has occurred. It acts like one or both of the gears are too large.

[gzumwalt]

Hi nlkirchn,

I'm sorry for the difficulties you are having.

Please check the following:

1) Check to make sure none of the frame or carriage components are warped (I had a carriage side warp slightly, so I had to wash my glass build plate and print it again).

2) Check to make sure all the build plate side "ooze" has been removed from the gears as this will cause binding. I'm now using a handheld motor tool running at slow speed with a wire brush attachment to clean the gear teeth as opposed to filing, it is much faster and I'm slowly getting better at it.

3) Check to make sure the floating pinion gears rotate freely about "Gear, Compound ((8, 1.5), (40, 1.5))" before the axles and wheels are installed. If not, you may need to slightly loosen the carriage axles and bolts.

4) Check to make sure the gear motor operates freely and rotates the carriage assembly fully to the crossmember stop, then releases, before the axles and wheels are installed.

5) Check to make sure the carriage is installed in the proper orientation as shown in the exploded views (yes, I did do that, once).

Hopefully, these items will help. An any event, please keep me updated and I will try to come up with other solutions.

Again, I'm truly sorry for the difficulties you've encountered.

Greg

[nlkirchn]

Thanks for the assistance, my windup bunny is chasing the Energizer bunny now. I was unaware that my extruder had gone out of tune I was over-extruding and it affected the gears mostly. They were coming out too large and that explains why I had to chase every thread and ream every hole to make things go together. Once I recalibrated the extruder things went together as expected. Its another addition to my gzumwalt collection.

[gzumwalt]

Hi nlkirchn,

You are very welcome and I'm glad you were successful!

Again, I'm truly sorry for the difficulties I caused.

Greg

[nlkirchn]

I seem to create my own problems I just need your expertise to solve them. If you keep creating new things I'm going to need a bigger shelf for my gzumwalt collection.LOL

[gzumwalt]

Hi nlkirchn,

Well, I create enough problems myself before a design is completed, so I'm in the same boat (or bunny in this case). I try to catch all errors before publishing a design, and, well, more than once, as in this case, I've missed.

:)

Greg

[dkingma]

Hi gzgumwalt, Everything printed beautifully but I have a question.. I'm trying to connect the spring and paul onto the Knob and Axle, but the length of the hex section on the knob is not long enough to accommodate both the spring and paul. In fact, when I press the spring onto the hex section of the knob/axle, the hex section doesn't protrude at all from the spring when the spring is bottomed out on the frame. What am I doing wrong? Thanks!

[gzumwalt]

Hi dkingma,

You are doing nothing wrong, it's my fault, and I'm truly sorry for the difficulties.

I made a mistake and uploaded an incorrect "Frame, Left.stl" and have since uploaded the correct "Frame, Left.stl". There is a "spacer" extending from the hole for "Knob and Axle.stl" in the left frame that should not be there (the spacer also appears in the assembly images in "Step 3: Assemble the Frames"). The spacer needs to be removed using a small hand saw, motor tool with a cutoff wheel at slow speed, or a modeling knife using multiple passes. Once removed, when "Spring.stl" is pressed onto "Knob and Axle.stl", the spring should be within .4mm from the inside of "Frame, Left.stl". If you do not have tools to remove the spacer, you will unfortunately need to print the new "Frame, Left.stl".

My sincerest apologies for my error.

Greg

[rjford]

Hello. I too had a problem with the spring, so I actually just designed my own knob and axle. But, I would prefer to use the correct one.
I just downloaded Frame, Left.stl again....but it looks exaclty the same.
Was there a problem uploading the new file?

[gzumwalt]

Hi rjford,

I downloaded the latest "Frame, Left.stl" and it is the latest with the spacer removed from the hole for "Knob and Axle.stl". Could you pease try again and check to see if you receive the frame with the spacer removed?

Many thanks, and I'm truly sorry for my error.

Greg

[kshowell]

Thank you so much for sharing. This is a fun little machine.

[gzumwalt]

Hi kshowell,

Many thanks, I'm glad you enjoyed it!

Greg

[jimbarstow]

i printed this for my granddaughter and ran into a problem. The "knob and axle" has a hex portion that locks into the spring and pawl. When placed in the frame, however, there is a riser on the frame that covers most of this hex section and prevents them from interlocking. It also makes this section of the assembly too wide. It looks like the riser on the left frame shouldn't be there.I've attached a picture with the left frame with the knob and axle and spring assembled. You can see that the hex portion ends before exiting the spring.

[gzumwalt]

Hi jimbarstow,

I'm truly sorry, I uploaded an old "Frame, Left.stl" and have since uploaded the correct "Frame, Left.stl". The riser indeed should not be there, and can be removed with a small saw or motor tool if you have those tools available.

Again, my sincerest apologies.

Greg

[jimbarstow]

Thanks.
I'm trying a fix I did myself using the new mesh editing tool in fusion; gave me an excuse to learn a new fusion feature. I'll compare it with what you uploaded to see if it works as well.

Perhaps you can answer a question..

Why do people only upload STL files for 3D printed items? Do the sharing sites not allow the underlying cad files? It absence of the cad file really limits the usefulness of sharing. I'm about to share some of the things I've been working on and hope to include the fusion project. To me, it's like sharing source code versus a binary.

[gzumwalt]

Hi jimbarstow,

Best wishes on your success using the mesh editor!

For me, it depends on the project as to why I upload the cad files. I've created Instructables where I do provide the cad files for tutorials such as https://www.instructables.com/id/Designing-a-Simpl... and this https://www.instructables.com/id/Designing-a-Param... and for designs allowing customization such as this https://www.instructables.com/id/Ping-Pong-Popper/...

But for most designs, I simply publish the STL files for printing as deriving the individual components in the correct orientation from the CAD file places too much burden on the person who simply wants to print a model.

Greg