Author Topic: Chinese 25mm Gearboxes (For Beetleweights)  (Read 5030 times)

IanMcMahon

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Chinese 25mm Gearboxes (For Beetleweights)
« on: July 12, 2015, 01:34:27 pm »
I spent 4 hours today going through my 25mm Chinese beetle gearmotors and have the following results:
1.   The gearboxes can use motors with a bolt pattern of 14mm or 17mm. These correspond to Mabuchi 280 and 370 motors.

2.   The stock pinions are brass 12T 0.4 mod with a 2mm bore. Steel versions are available here although they will probably need to be filed to reduce the width. http://www.lynxheli.com/product_info.php?products_id=24706

3.   The 500 RPM gearbox has a ratio of 24.7:1. The gearbox is longer because they added a 20T to 12T stage. I bought this one: http://www.ebay.com/itm/25GA-DC12V-500RPM-2000mA-High-Torque-Electric-Gear-Box-Motor-25MM-2A-2-5kg-cm-/181635271676?pt=LH_DefaultDomain_0&hash=item2a4a4e4bfc . It actually runs at 600 rpm at 12 volts. The motor stalled at 2.3A at 12V. The gearbox itself might be a good choice for the brushless drive crowd.

4.   The 1000 RPM gearboxes have a ratio of 14.8:1.

5.   The Kitbots gear motor stalled at 1A at 2.3 Volts. At 12V, it should stall at 5.2A. I think this is why Pete sells that particular gearmotor; it is roughly twice as powerful as the other 1000 rpm motors.

6.   This 1000 RPM gear motor stalled at 2.1A at 12V. http://www.ebay.com/itm/3A-DC-12V-1000RPM-25GA-3000mA-High-Torque-Electric-Gear-Box-Motor-25MM-1-5kg-cm-/181635279753

7.   The motors are consistent between batches but are not all the same. The motors seem to have a kV between  1240 and 1300 rpm/V. I have tried to look up the model numbers, but they seem to be from assorted lots sold for other purposes and datasheets aren’t really available.

8.   The Mabuchi RC-280RA-2485 would be a good motor choice if you want to run at lower voltage. It is available from Banebots at http://banebots.com/pc/MOTOR-BRUSH/M2-RC280-60. At 7.4 volts, it would give 880 rpm with the 14.8:1 gearbox for 2.3 ft/s with 2” wheels. The Kitbots gearmotor would only do 620 rpm at this voltage for 1.6 ft/s with 2” wheels.

Harry Hills

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Re: Chinese 25mm Gearboxes (For Beetleweights)
« Reply #1 on: July 12, 2015, 03:15:06 pm »
Thank you for this information, very helpful.

Jeff Gier

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Re: Chinese 25mm Gearboxes (For Beetleweights)
« Reply #2 on: July 12, 2015, 08:54:50 pm »
Great post!  I've heard that the more powerful 25mm motors have a plastic back.

Luke

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Re: Chinese 25mm Gearboxes (For Beetleweights)
« Reply #3 on: July 20, 2015, 10:58:09 am »
Thanks, quite useful for beetle I'm plotting.

adrian

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Re: Chinese 25mm Gearboxes (For Beetleweights)
« Reply #4 on: July 30, 2015, 04:10:56 pm »
Yes, thank you! Does your non-kitbots one have a plastic or metal back? Is there anything else we can use to tell the high and low power ones apart? I can test my plastic back ebay motor for the stall current when I get home.

adrian

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Re: Chinese 25mm Gearboxes (For Beetleweights)
« Reply #5 on: August 03, 2015, 01:23:04 am »
I just tested and then took apart my 1000rpm motor with the plastic back that I bought on eBay in 2013. For stall current, I tested at 1V because apparently I blew the 10A fuse in my meter. When the motor was cold, I got 175mA, or 2.1A at 12V. Over the next 30 seconds, current rose to 225mA, or 2.7A at 12V, as the coils heated up. The motor can was still cold to the touch. These seem in line with Ian's measurements of the 500rpm eBay motors.

When I opened it up, the gearbox had three sets of motor mounting holes, with 14, 15, and 17mm spacing. Its a shame there's no 16mm spacing, as that's a common dimension for 24mm brushless inrunners. I wonder if it would be possible to expand the holes slightly to fit.