Chapman GP7 Project

Chapman GP7 Project

Postby ConnRiver » Fri May 27, 2016 3:42 pm

I'm posting three screen shots of a Mashima 1024 motor I drew in 3D. It was created using an online spec sheet. The flywheel is my concoction, though. Perhaps it is too large? Somewhere here, I have an article or two about flywheels. . . .

Soon, I'll post a 3D drawing of a possible frame, based on the HO Proto 2000 GP7 model. After that, I'll dig into drawing a tower truck (with worm and spur gears), and finally, motor-truck linkage.

Sure would like critiques/suggestions as I move along toward my goal of creating a working TT scale power chassis. Once a design meets with general approval here (assuming one can), I'll CNC cut the parts and see what results. This might be kinda fun. . . .

Brian C. / Cedar Rapids, Iowa
Attachments
1 - Mashima 1024 - Top.jpg
2 - Mashima 1024 - Side.jpg
3 - Mashima 1024 - End.jpg
Last edited by ConnRiver on Fri Jul 01, 2016 1:00 pm, edited 1 time in total.
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Re: Chapman Chassis - Frame

Postby ConnRiver » Fri May 27, 2016 4:11 pm

Would a frame based on the Proto 2000 GP7 model serve well? Or, would someone here disagree?

Brian Banna, a modeler of renown, has developed a chassis based on the prototype's profile. In the below link can be found Brian B.'s construction blog, if you'd care to take a look. The frame he designed is plastic, but I believe he writes it would serve as a master for metal casting:
http://www.pbase.com/image/51606762

(Brian B. has some interesting You Tube videos, too.)

His frame is designed so that an Athearn plastic walkway (with end steps) slips over the top. In TT scale, though, I wonder if a frame should have "wings", metal that extends outward to under the walkway and end platforms.

-Brian C.
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Re: Chapman Chassis Project

Postby dwyaneward » Fri May 27, 2016 5:54 pm

Brian,

have you seen D Rickman 3d Printed trucks
https://www.shapeways.com/product/VJ8WV ... 10mm-motor
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Re: Chapman Chassis Project

Postby ConnRiver » Fri May 27, 2016 6:10 pm

Dwayne, it's interesting, but . . . lot of work yet to be done on the design, I see. I wonder what (2) 10mm x 12mm motors would cost, compared with (1) 10mm x 24mm motor.

The axle spur gears are driven by worms, also interesting.
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Re: Chapman Chassis Project

Postby ConducTTor » Fri May 27, 2016 9:20 pm

dwyaneward wrote:Brian,

have you seen D Rickman 3d Printed trucks
https://www.shapeways.com/product/VJ8WV ... 10mm-motor


It's a good looking design. However, I fear the lack of flywheels will make for poor drive characteristics. I'm also sceptical of that being able to swivel within a narrow hood.
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Re: Chapman Chassis Project

Postby Bernd » Fri May 27, 2016 9:43 pm

dwyaneward wrote:Brian,

have you seen D Rickman 3d Printed trucks
https://www.shapeways.com/product/VJ8WV ... 10mm-motor


Ken and I collaborated on designing tender drives back in 2013 on MRH. Here's the link to that page.

http://model-railroad-hobbyist.com/node/17247

It starts on the first page. Scroll down a bit and you'll see it. i started the post. There may be more posts around that time frame, 2013-2014 on MRH.

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Re: Chapman Chassis - Frame

Postby Bernd » Fri May 27, 2016 9:45 pm

ConnRiver wrote:Would a frame based on the Proto 2000 GP7 model serve well? Or, would someone here disagree?


Not familiar with the Proto 2000 chassis. Anything like the Athrean frames?

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Re: Chapman Chassis - Frame

Postby ConnRiver » Fri May 27, 2016 9:55 pm

Bernd wrote:Not familiar with the Proto 2000 chassis. Anything like the Athearn frames?
Bernd


Here's a 3D drawing of the P2K HO GP7 frame I did a few years ago. It's pretty accurate.
Attachments
Frame - P2K.jpg
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Re: Chapman Chassis Project

Postby ctxmf74 » Sat May 28, 2016 2:27 am

"It's a good looking design. However, I fear the lack of flywheels will make for poor drive characteristics. I'm also skeptical of that being able to swivel within a narrow hood."

Yeah, dual motor drive also add the complication of getting the two trucks to run smoothly together. I think a simple basic single motor drive would be better than something unproven. The MTB switchers apparently have some motor quality issues but the drive in my two locos runs great. Nice and slow speed and throttle response with a cheap Digitrax decoder. I don't think design is a problem for prospective TT loco manufacturers, it's more experience and how to turn design into production reality. One of the major loco builders in other scales would have no problem turning out great TT locos if they were inclined to make the investment..... DaveB
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Re: Chapman Chassis Project

Postby Richard-B » Sat May 28, 2016 9:39 am

I think there are good, rational design reasons why commercial products tend to settle on a BCP (Best Current Practices) solution:
  • Motor Size / Power / Cost
  • Gear train complexity / part count / cost
  • Power truck turn angle (i.e. minimum radius)
  • Potential DCC compatibility (~single motor)
The result: (SWAG - order of magnitudes)
  • 0.01% Multi-motor trucks
  • 2% Motor per truck
  • 2% Tank Drive
  • 95.9% Single motor + gear tower trucks
That said... for one-off or limited-run solutions, ANYTHING can be made to work.

Hey... How many of us remember replacing the rubber bands in the original Athearn Hi-Fi drives????
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