[MOC] Pullback motor experiment: Running dino (linkage)

[Joostv]

This is a little experiment with a pull-back motor. The idea was to do something other than wheels, so I tried legs 😊.
I got this to work quite reasonably as you can see in the video.

The idea was to have a linkage for the feet that is linear on the front to back movement, but moves in an arc on the back to front movement so the feet can overlap. The overlap is in the center.
I have made instructions (free ofcourse) which are here: https://rebrickable.com/mocs/MOC-252160/MejoliDesign/md007-running-dino-experiment
You can just scroll through the PDF and see the dino from various angles. This will give you a better idea of how it was built. 

I managed to include a moving tail, which really helps balancing the dino. With the tail the run was much more stable than without it.
I have made attempts to make it a bit prettier, but basically any additions downgrade performance or upset the balance.

The sprint is short: 1 tot 1.5 meters. If the power runs out it falls, and power runs out quickly with a pull-back motor. Depending on how well it was positioned at the start and how well you guide the first step the sprint will go straight, curved or it will do something weird like hop on one foot and rolling on its back. I think you can compare it to rolling a coin: it takes a bit of practice. 

In one way the pull-back motor is the excellent choice for this. The advantage of the pull-back motor is that it will accelarate hard if load is removed. This is precisely what happens in moments when both feet are off the ground. Due to the acceleration of the pull-back motor in this moment, the feet will quickly regain contact with the ground again. You can see these little accelerations in the slow motion part of the video if you look closely. 

I had quite a lot of fun experimenting with this. So if you want to have a bit of fun building something small that jumps/runs/hops/flaps/... I recommend playing around with a pull-back motor 😉

 

[2GodBDGlory]

That's really impressive! Nice work!

[gyenesvi]

Indeed, this is really neat mechanically, and the pullback motor is a great fit for this! The result is quite smooth movement!

[Joostv]

10 hours ago, 2GodBDGlory said:

That's really impressive! Nice work!

Thanks 😊 

9 hours ago, gyenesvi said:

Indeed, this is really neat mechanically, and the pullback motor is a great fit for this! The result is quite smooth movement!

Thanks 😊 I was pleasantly surprised by the performance of the pull-back motor in this application.

[Jurss]

This is cool, and well implemented!

[Bartybum]

Oh man this scratches my itch in just the right way, I love it

[Mikdun]

That's so funny! 

But also innovative and real-life like. Pull back motor put to good use!

[Davidz90]

Wow, this is really cool!

[Joostv]

8 hours ago, Jurss said:

This is cool, and well implemented!

Thanks 😊

8 hours ago, Bartybum said:

Oh man this scratches my itch in just the right way, I love it

😂 Thanks!

4 hours ago, Mikdun said:

That's so funny! 

But also innovative and real-life like. Pull back motor put to good use!

Thanks! I learned to announce tests of this one. First succesfull test run in the living room caused a little scream..  Bit too life-like 😉

3 hours ago, Davidz90 said:

Wow, this is really cool!

Thanks 😊

[Toastie]

@Joostv strikes again.

Man - this is so nice to watch. For one, how the lill dino runs away ... but then after sharply sucking in air - revealing the mechanism behind it. 

Simply fantastic.

All the best
Thorsten

[Jundis]

Watched it 10 times and giggled all the way, what a cool movement :D

[Timewhatistime]

This little wind-up dinosaur once again proves that 'simple' ideas, well executed, are still the best. Not only is the motion very satisfying, the little beast really runs! I really like it, just as the other members do.

Edited February 21 by Timewhatistime

[Joostv]

On 2/20/2026 at 11:39 PM, Toastie said:

@Joostv strikes again.

Man - this is so nice to watch. For one, how the lill dino runs away ... but then after sharply sucking in air - revealing the mechanism behind it. 

Simply fantastic.

All the best
Thorsten

On 2/20/2026 at 11:43 PM, Jundis said:

Watched it 10 times and giggled all the way, what a cool movement :D

19 hours ago, Timewhatistime said:

This little wind-up dinosaur once again proves that 'simple' ideas, well executed, are still the best. Not only is the motion very satisfying, the little beast really runs! I really like it, just as the other members do.

Thanks for the positive feedback all 😊 

[AJB2K3]

Wow, Sweet. Now there a start to a technic set we haven't seen for decades.

[Holodoc]

Absolutely cool build!
I in general like moving LEGO and even better: This one is made with just a handful of parts - very ingenious!

A well deserved frontpage! 

[Joostv]

21 hours ago, AJB2K3 said:

Wow, Sweet. Now there a start to a technic set we haven't seen for decades.

19 hours ago, Holodoc said:

Absolutely cool build!
I in general like moving LEGO and even better: This one is made with just a handful of parts - very ingenious!

A well deserved frontpage! 

Thank you both! 😊

[SpacePolice89]

I can't stop watching this! Great build and funny! 

[Thirdwigg]

Very cool build. I'll have to give this a build and try it out myself.

[Zerobricks]

What an amazing a cute model! Reminds me of the road runner.

[Joostv]

On 2/24/2026 at 2:08 PM, SpacePolice89 said:

I can't stop watching this! Great build and funny! 

Thanks, glad you enjoy it 😊

On 2/24/2026 at 2:14 PM, Thirdwigg said:

Very cool build. I'll have to give this a build and try it out myself.

Thanks! Have fun 😊 check the first pages of the instructions for alternative parts of you don't have DIGatron.

On 2/24/2026 at 7:04 PM, Zerobricks said:

What an amazing a cute model! Reminds me of the road runner.

Thanks 😊 I watched road runner a lot as a kid 😊

[SaperPL]

Really cool model. Any chance that you would figure out a way for it to have a spool with a thread for winding it up that would be guided through the tail?

It might be a strong contender to ideas or bricklink designer program if you had a solid reliable way of winding it up without holding the mechanism by the gears / feet to not unwind.

I'm also imagining something like the tail being a pipe guiding the thread for winding up and once the thread is spooled up at the end of the run, the thread pulls the tail up and it does something like for example if it was a peacock and at the end tail spreads. The only problem i see is how to not make it overcomplicated and heavy in comparison to what you already did. But the core of wind-up mechanism seems like an important piece missing from it being polished.

Anyway great job!

[Timewhatistime]

@Joostv Please, is there any possibilty for you to decrease the size of the instructions' file?

Rebrickable requests a registration and a login for "a file of this size" (14,6 MB).

[2GodBDGlory]

I had to hop on the hype and build a cute little guy for myself! It's pretty fun! I ended up sticking an axle with 24T gear into a cordless drill for super fast rewinds, which worked quite nicely!

[Joostv]

On 2/26/2026 at 8:47 PM, SaperPL said:

Really cool model. Any chance that you would figure out a way for it to have a spool with a thread for winding it up that would be guided through the tail?

It might be a strong contender to ideas or bricklink designer program if you had a solid reliable way of winding it up without holding the mechanism by the gears / feet to not unwind.

I'm also imagining something like the tail being a pipe guiding the thread for winding up and once the thread is spooled up at the end of the run, the thread pulls the tail up and it does something like for example if it was a peacock and at the end tail spreads. The only problem i see is how to not make it overcomplicated and heavy in comparison to what you already did. But the core of wind-up mechanism seems like an important piece missing from it being polished.

Anyway great job!

Thanks! A quicker / easier way to wind up, like pulling a thread as you suggested, would be great. The problem with adding it to the dino itself would be that it adds weight and impacts the balance. Adding a spool to the wind up tool should be feasible, but it would require an additional solution to wind up that spool. Which could be something simple, like rolling it over the floor. That would be worth a try I think. Another solution would be something electric, like a Lego version of @2GodBDGlory's drill solution.

11 hours ago, Timewhatistime said:

@Joostv Please, is there any possibilty for you to decrease the size of the instructions' file?

Rebrickable requests a registration and a login for "a file of this size" (14,6 MB).

Hi @Timewhatistime, I didn't know about this size restriction. I will try and see if some compression can be achieved at the cost of resolution and will upload it as a seperate version. This way you should be able to select the smaller version.

10 hours ago, 2GodBDGlory said:

I had to hop on the hype and build a cute little guy for myself! It's pretty fun! I ended up sticking an axle with 24T gear into a cordless drill for super fast rewinds, which worked quite nicely!

Thanks! and thanks for sharing that solution! I will be exhibiting (for the first time) next month and will definitely bring along my cordless drill 😉

[Joostv]

16 hours ago, Timewhatistime said:

@Joostv Please, is there any possibilty for you to decrease the size of the instructions' file?

Rebrickable requests a registration and a login for "a file of this size" (14,6 MB).

@Timewhatistime I have added a low-res / minimum size version that is under 5MB at the cost of visible compression in the instructions. Please, let me know if this works.