Hank Fletcher

For the record, it wasn't me!

You came to the same conclusion I had: that it might be easy enough to modify the gearboxes to accommodate motors of slightly different shapes. Ideally, I thought I'd see if I could find any other motors that were as close to exact as possible. I still say the 4.5V nominal rated FC-130 would be a better product for Tamiya to use, but maybe it wasn't in production when they first developed their various gearboxes?

Let me know how easy you think some modification will be once you get your gearbox. Making sure the shaft is where it ought to be seems like the biggest challenge. I can see some leeway with gearbox models with plastic frames, but the one I'm most interested in modding now is the universal gearbox, which has a metal frame.

zanes

Ah! I thought you meant the plastic ones, I'm getting the double gearbox. Looking at photos of the universal one, I think it would be possible to modify it as well, a motor bracket would need to be made though. Is it more power you're after, or higher voltage tolerance?

Hank Fletcher

I thought it'd be fun to see if I could put a bit more power through the gearboxes, but now knowing what I know about the FC-130, and it being essentially dimension-perfect to the FA-130, I just wish the FC-130 came stock with the Tamiya gearboxes instead. I guess my main criteria for that desire is that the FC-130 seems better suited to the specs for the above mentioned h-bridge IC (more appropriate voltage and current ranges with the FC-130), so it's mainly a convenience-of-compatibility issue.

3v0

The SN754410 powers the motor from VCC2. If you want to run them at less then 5 volts you could lower the voltage. The datasheet says it will work between −0.5 V to 36 V.

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blueroomelectronics

Tamiya also makes some HE gearboxes with more torque and bigger motors.

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zanes

Right, my gearbox arrived today. A few observations;
It's a very fast gearbox, I've built it in the lowest ratio configuration. Without PWM this will be more than sufficient. PWM would allow the next ratio to be used, I think the top two will be useless for robotics.
The gearbox is a strong unit, so it should be able to take a more powerful motor.
Now the good bit, if you were to remove everything to the left of the red line in my attachment you would be left with a flat bulkhead with holes in it. This would be easy to adapt to take a larger motor (with bracket and suitable gear).
Having said this, the gearbox and motor combo is already impressively fast and powerful.

Attached Images

1024x768-robot.JPG (430.5 KB, 9 views)

blueroomelectronics

Problem might be the motors are side by side, only a slight space exists between them. A larger diameter motor won't work.

Attached Images

MongooseGearbox.png (86.8 KB, 4 views)

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zanes

I think if you moved the spur gear to the middle of it's shaft, you could fit slightly larger motors. Or you could use the single motor version, or just use a larger motor and different gearbox (probably the best option!)

blueroomelectronics

Those little gearboxes have plenty of torque at 114:1 or higher, what sort of load are you trying to move.
The little brass bearing won't hold out for big loads, you'd realistically need ball bearings.

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zanes

It's hank who wants to mod them, to take a higher voltage motor from what I can tell. I just thought it was fun to have a nosy at the gearboxes to see what could be done!

Hank Fletcher

I'd thought about that for the universal gearbox, which has up to about 700:1 gear ratio. Observing the small robot arm models they have at the local community college, I noticed that the servo-driven joints have additional structure axles. What I mean is, the servo horn is connected to the joint, but the design allows for radial movement of the joined parts by the servo, but there is no force perpendicular to the servo shaft on the servo shaft. Instead, there's another part that takes the perpendicular-force load. I can remember how that did that on the opposite end of the servo horn, but I'm a little fuzzy at how they went about it at the business end - I'd have to see it again. Definitely a bushing not a bearing solution, but then they were small robots made of fairly robust metal (aluminum?).