Custom micro motor adapter

[msx80]

so i've always desired to have smaller motors than the ones available in PF or Mindstorm (those are huge), they're too bulky to create a small motorized model. I've made some experiments and finally made a working micro motor with adapter for Lego.

 

The assembly have a footprint of about 2x4 studs (with a little extra on the back). Height is a little more than one brick (can be enclosed in a 1 brick + 1 plate).

The cool things about this gearmotor that makes it perfect are:

• the rotating point is about the same size of a Lego bar (3mm) greatly helping with centering the adapter
• it comes with many gearing, mine is 100:1, quite slow but super powerfull
• works with voltages from 6 to 12, so can be wired directly to PF and works with IR correctly at all speeds.

Creating the adapter was not easy and required modifications on both the motor and the bricks, but it was still easier than with other motors i tested. Stuff needed: the motor, a 2x1 technic brick, a half pin/half axle (i used legos from my super old collection to avoid destroing new legos :P), superglue, some power tool and stuff. It was all pretty cheap, the motor costs between 15 and 3 € depending on where you buy it.

I'm very satified with it, i plan to attach a regular 9V battery as a power source, that is much smaller than the Lego battery box. That should give me basically the smallest possible motorized platform :P

Here it is in use:

 

 

 

Some videos (i hope they're visible, otherwise you can check my flickr):

 

 

 

 

[Sariel]

https://www.bricklink.com/v2/catalog/catalogitem.page?P=2986#T=C

[Capparezza]

8 minutes ago, Sariel said:

https://www.bricklink.com/v2/catalog/catalogitem.page?P=2986#T=C

Yeah, and starting at 15 bucks for a working one... postage NOT included! I dare to guess that the OP's version is much cheaper than that.

 

@msx80 I'd appriciate any info about that small motor. Where is it from? Gutted out from older toys? Or new? What are the specs?

[msx80]

8 minutes ago, Sariel said:

https://www.bricklink.com/v2/catalog/catalogitem.page?P=2986#T=C

yeah i know, loved that part, but it's not in production since 2001 and prices are no less than 15€ for a working used one (no younger than 17 years old). And it's not PF compatible (while still being 9V).

Anyway, that's the size i want for a Lego motor, it would be awesome if they made a similar part today.

PS huge fan of your work sariel :) you rock!

2 minutes ago, Capparezza said:

 

@msx80 I'd appriciate any info about that small motor. Where is it from? Gutted out from older toys? Or new? What are the specs?

I purchased it new from Sparkfun some years ago, i kept it on my electronic parts till some days ago. Specifications are as follow:
 

Quote

 

Features:

• Voltage: 6 - 12 Volts
• Gear Ratio: 100:1
• Stall Torque: 12/25 oz-in. (6/12V)
• Speed: 140/270 RPM (6/12V)
• No Load Current: 40/80 mA (6/12V)
• Stall Current: 360/1600 mA (6/12V)
• DC Reversible

Dimensions:

• Motor Size: 26 x 12 x 10mm
• Shaft Size: 3mm Diameter x 10mm Length
• Weight: 17g

 

At the time i paid mine 15 €, but now you can find them on sites like aliexpress for less than 3 € each (they look identical, but i'm not 100% sure they're the same production. I've ordered some days ago, when they'll arrive i'll check). They come in a wide range of gear ratio.

[TechnicRCRacer]

48 minutes ago, msx80 said:

And it's not PF compatible (while still being 9V).

Well it is, i think. You can attach a normal 9V wire to the motor and a PF extension wire to the 9V wire.

[Capparezza]

@msx80 Thanks a lot Maybe you can post back when you get your latest shipping?

[msx80]

43 minutes ago, TechnicRCRacer said:

Well it is, i think. You can attach a normal 9V wire to the motor and a PF extension wire to the 9V wire.

ah didn't know that

16 minutes ago, Capparezza said:

@msx80 Thanks a lot Maybe you can post back when you get your latest shipping?

sure, will do

[Philo]

Very cute! Too bad it's a tad longer than a 2x4...

[msx80]

2 minutes ago, Philo said:

Very cute! Too bad it's a tad longer than a 2x4...

indeed, but you have to leave some room for the cable anyway so not that bad

[Philo]

Well, if it was significantly shorter AND made room for cable...

 

[Void_S]

3 hours ago, Philo said:

Very cute! Too bad it's a tad longer than a 2x4...

Hmm... What if use 2x4 brick without a short side, inner stud-holders (those three cylinders in the middle) and a hole for the cable as a cover for this micro motor? It should be 2x5 brick with motorized axle as result, I suppose.

Edited April 13, 2017 by Void_S

[kolbjha]

6 hours ago, msx80 said:

Features:

• Voltage: 6 - 12 Volts
• Gear Ratio: 100:1
• Stall Torque: 12/25 oz-in. (6/12V)
• Speed: 140/270 RPM (6/12V)
• No Load Current: 40/80 mA (6/12V)
• Stall Current: 360/1600 mA (6/12V)
• DC Reversible

I don't have extensive knowledge about DC motors, but assuming I can interpolate between 6V and 12V to find 9V characteristics for stall torque and speed (I guess the speed referred to above is no-load speed), means that for 9V:

• Stall torque: 18.5 oz-in. = 13.06 N-cm
• No-load speed: 205 RPM

Using Philo's site as reference:

As RPM/Torque curve is linear, it means that max. power will be at half of no-load speed (and consequently torque that is half the stall torque), this motor will have a max. power of 205/2 RPM (= 1.708 rotation/sec) x 13.06/2 N-cm (= 0.0653 N-m) x (2xPi) = 0.701 W

Comparing with PF M motor and measurements from Philo:

• Stall torque: 11 N-cm
• No-load speed: 405 RPM
• Max. power = 405/2 RPM (= 3.375 rotation/sec) x 11/2 N-cm (= 0.055 N-m) x (2xPi) = 1.166 W

Summing up, comparison with PF M motor:

• Apx. 20% higher torque than PF M motor
• Apx. half the RPM of the PF M motor
• Apx. 60% of the power of the PF M motor

Pretty impressing for that size IMO. But of course, I guess some of the reason the PF motors are bigger is the housing and BI's.

Philo, or others with knowledge about DC motors, please correct if I am wrong, or comment.

Edited April 13, 2017 by kolbjha

[VKTechnic]

4 hours ago, Philo said:

Well, if it was significantly shorter AND made room for cable...

 

Could shave down that 1x2 Technic brick?

[kolbjha]

3 minutes ago, VKTechnic said:

Could shave down that 1x2 Technic brick?

Well, that 1x2 Technic brick for sure serves as a BI, and if I understand msx80 correctly, he is using a axle pin, as it makes connection to the motor axle easier.

And to msx80: Very interesting indeed, thanks for sharing 

[andythenorth]

This looks great.  

I hold out hope that TLG produces a PF 's' motor with roughly these dimensions 

[Boxerlego]

It does look great. @msx80 Excellent work on the Micro Motor. It looks like it could fit perfectly in between two plates one one top and one on bottom. Also it looks like it could be one Strong Micro Servo Motor.

[msx80]

2 hours ago, VKTechnic said:

Could shave down that 1x2 Technic brick?

You'll lose the only connection point (top and bottom studs) for the stator. 

2 hours ago, kolbjha said:

Well, that 1x2 Technic brick for sure serves as a BI, and if I understand msx80 correctly, he is using a axle pin, as it makes connection to the motor axle easier.

And to msx80: Very interesting indeed, thanks for sharing 

Thanks :) Yes i'm using an axle pin. The design "waste" a brick but makes things much simpler to build.

1 hour ago, Boxerlego said:

It does look great. @msx80 Excellent work on the Micro Motor. It looks like it could fit perfectly in between two plates one one top and one on bottom. Also it looks like it could be one Strong Micro Servo Motor.

Not really, the motor plate is a little higher than the brick level, it requires an additional plate. On the bottom is flush, you can attach a tile/plate combo but not a plate, for there's no space for the studs. Here's a couple of images:

 

 

4 hours ago, Void_S said:

Hmm... What if use 2x4 brick without a short side, inner stud-holders (those three cylinders in the middle) and a hole for the cable as a cover for this micro motor? It should be 2x5 brick with motorized axle as result, I suppose.

it would be possible in principle, but not easy to align precisely. It would be 1 plate taller than the frontal brick (for the metal plate, no real problem there) but the gearbox is hard to attach stuff to, you'd have to glue it down to the motor body, perhaps using a lego scaffold to align it. Might try your idea!

Here's the basic components:

 

[PorkyMonster]

Here's a matching servo

way smaller than Lego's servo...

Edited April 14, 2017 by PorkyMonster

[syclone]

Very interesting , will wait for a test of the cheap ones . I guess after a bit of cutting , sanding and glueing it would be possible to make a case for that motor from an empty PF housing. ( PF M-motor cut down to 4 studs would work since there's plenty of space for a wire inside)

[msx80]

8 hours ago, PorkyMonster said:

Here's a matching servo

way smaller than Lego's servo...

I actually considered adapting a servo too :) but they're too distant from PF, both in voltage, electronics and size. Would require extra circuitry etc.

2 hours ago, LXF said:

Very interesting , will wait for a test of the cheap ones . I guess after a bit of cutting , sanding and glueing it would be possible to make a case for that motor from an empty PF housing. ( PF M-motor cut down to 4 studs would work since there's plenty of space for a wire inside)

will report when they arrive :) aliexpress usually take ages to ship so it won't be soon.