3D printed motor block

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ge_rik
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3D printed motor block

Post by ge_rik » Thu Apr 13, 2023 1:44 pm

Just finished off my second 3D printed motor block for my GVT Glyn loco. The Bachmann block I used originally was underpowered (seems to be an issue for me with Bachmann blocks), so I 3D printed my own using the ubiquitous MFA Como 918D 30:1 gear motor.
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It was no better in terms of hauling capabilities than the Bachmann block. So, to coin a phrase, I "went large!". I adapted the motor block to take an MFA Como 942DLN gear motor with 50:1 reduction. Somewhat of a beast compared to the 918D, but I managed to squeeze it into the capacious body of the GVT Glyn.
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I would imagine this loco (with sufficient ballast weight) now has the capability to haul almost all the stock on my railway. Overkill, maybe, but I certainly can't complain about its pulling power now.




I think these blocks are probably have somewhat of a niche appeal, but would be happy to upload the files if there is any interest.

Rik
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philipy
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Re: 3D printed motor block

Post by philipy » Thu Apr 13, 2023 1:57 pm

That loco looks really good with those coaches, and it is certainly very smooth running.
Without checking its dims, I'd guess that motor is physically too big to fit in a 32mm chassis ( I realise that yours is 45mm)?
Philip

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Peter Butler
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Re: 3D printed motor block

Post by Peter Butler » Thu Apr 13, 2023 2:30 pm

Hi Rik, I watched your video before seeing it posted here, another triumph for your chassis construction method. That seems to be a huge motor and needs to have a large space to conceal it inside a loco, there is an alternative which I have used in the past.....
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The same motor is also used by GRS in their SM32 chassis unit and just fits between the wheels on a short chassis.....
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It can also be used to drive two axles via a 1:1 bevel gear system, similar to the one you have done.....
IMG_3068.JPG
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This requires an extended chassis.
The best things in life are free.... so why am I doing this?

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ge_rik
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Re: 3D printed motor block

Post by ge_rik » Thu Apr 13, 2023 4:19 pm

Hi Peter
Thanks for the ideas. I do like the way you've used the bevel gears to provide four wheel drive. The motor you've used is the same as that I used in my first motor block (ie the MFA Como 918D with 30:1 reduction. Although it worked well, I found it didn't have enough power at 12v for some of my longer goods trains which is why I opted for the larger MFA motor.

I've since sourced a smaller Polulo gear motor (at Graeme(GTB)'s suggestion) which is nearer in size to the 918D but is supposed to be more powerful. It should fit between the frames of a 32mm gauge loco. I'll have a go at designing a motor block for it and let everyone know the outcome.

Rik
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Re: 3D printed motor block

Post by GTB » Fri Apr 14, 2023 1:23 am

ge_rik wrote: Thu Apr 13, 2023 4:19 pm Although it worked well, I found it didn't have enough power at 12v for some of my longer goods trains which is why I opted for the larger MFA motor.
What do you mean by not enough power? Did the loco stall with a heavy load, or did it wheel slip to a stop, as the fix is different.

Stalling - not enough torque, needs a bigger motor or higher gear ratio.

Slipping - needs more weight.


I've never owned a Bachmann large scale loco, so no experience. I know they use Mabuchi motors and typical of chinese made mechs, the plastic gears split..... Their use of bright plated driving wheel treads doesn't fill me with confidence either.


Like Gregh I like to take performance measurements of my mechs as I build them. The important numbers in this context are train rolling resistance and loco drawbar pull.

I measure both using a small digital spring balance and mine came from the local Jaycar branch years ago. They've stopped selling them, but they are widely available on Ebay. Usually described as being for weighing fish, or hand luggage......

This one is an Aust listing, but is typical of the breed. https://www.ebay.com.au/itm/26621537220 ... R6Stoc3vYQ


The rolling resistance of a train more or less doubles on a curve (which is why I use free wheel wheelsets) and it increases on grades as well. The increase on grades is a function of the train weight and the gradient and can be calculated, but is easier to measure with the spring balance.

As mentioned above, bright plated shiny driving wheels don't help traction. Neither do plastic driving wheels, if it comes to that.

With normal metal wheels on metal rails, the drawbar pull of a loco is about 20% of the weight on the driving wheels. Plastic on metal rails will be lower. Bullfrog Snot on the driving wheels has better grip, but I can't say I've ever seen a railway loco with bright green driving wheel tyres. Traction tyres, beloved of continental manufacturers, are an invention of the devil.......

Regards,
Graeme

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Re: 3D printed motor block

Post by ge_rik » Fri Apr 14, 2023 6:21 pm

GTB wrote: Fri Apr 14, 2023 1:23 am
ge_rik wrote: Thu Apr 13, 2023 4:19 pm Although it worked well, I found it didn't have enough power at 12v for some of my longer goods trains which is why I opted for the larger MFA motor.
What do you mean by not enough power? ........
Stalling - not enough torque, needs a bigger motor or higher gear ratio.
When climbing my 1:40 gradients I was having to open the throttle to full power with a fairly modest train and even then it slowed to a crawl. No wheelslip just lacking ooomph! I like to have a bit of additional power in reserve. My LGB motor block powered locos have no problem pulling far in excess of what their real life equivalents would have been able to haul. I seldom need that sort of power but it's comforting to know it's there. For example, (by coincidence filmed when Greg was here on a visit)



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Re: 3D printed motor block

Post by GTB » Sun Apr 16, 2023 9:39 am

ge_rik wrote: Fri Apr 14, 2023 6:21 pm When climbing my 1:40 gradients I was having to open the throttle to full power with a fairly modest train and even then it slowed to a crawl.
Hmmm......... MFA-Como motors aren't easily available in Oz, so I've never used a 918D and hadn't realised they were so gutless. I can see why Piko motor blocks are popular.

A big slow revving motor beats a small one screaming it's head off at max revs every time, but it's not easy to fit a big block Chevy in a Morris Minor. 8)

Since you have grades to worry about, you might find it an interesting exercise to do some rolling stock testing and investigate the rolling resistance of your stock. It can be measured with either a digital balance, or a simple inclined plane (basically a piece of track on a board). I think Greg has done more work on rolling stock testing than I have.

Graeme

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Re: 3D printed motor block

Post by drewzero1 » Wed Apr 26, 2023 12:44 am

Rik, I took your advice from the Youtube comments and went with a similar 25mm geared motor. It provides a beautiful smooth crawl, much better than I was hoping to achieve and much quieter than the screamin' toy motor I used in my scrapbashed industrial diesel. Next time I'll separate the motor block from the loco frame to save all of the tedious cutting and reassembling every time I change my mind on something. :thumbright:

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Re: 3D printed motor block

Post by ge_rik » Wed Apr 26, 2023 8:01 am

drewzero1 wrote: Wed Apr 26, 2023 12:44 am Rik, I took your advice from the Youtube comments and went with a similar 25mm geared motor. It provides a beautiful smooth crawl, much better than I was hoping to achieve and much quieter than the screamin' toy motor I used in my scrapbashed industrial diesel. Next time I'll separate the motor block from the loco frame to save all of the tedious cutting and reassembling every time I change my mind on something. :thumbright:
Pleased to hear it. I've been large scale modelling for seventeen years but still have a lot to learn. There are some incredibly talented modellers on this forum against whom my skills are extremely modest. The Railway Modeller magazine which has been published here for nearly 75 years used to have the subtitle - "For the Average Enthusiast" which is very much where I sit. But I hope that my blog and videos encourage others to come and join us.

Rik
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