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Nov 14, 2019, 01:43 AM
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DIY 500mg servo


Hello all

I've tested to make a small servo based on 125:1 4mm gearbox
https://solarbotics.com/product/gm25/

I use 3.2mm motor
8 pin chip from 1.7grs servo
49e hall sensor

total weight is 480mg very nice result

video :
micro servo 480mg (0 min 21 sec)


but my problem is the travel of the servo , and i dont know if my problem is from my hall effect choice ???

charles
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Nov 14, 2019, 08:24 AM
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Cool


Quite cool.
Afraid I cant help you with the Hall sensor.
But could you please show how to wire up the servo-chip? Thanx
Nov 14, 2019, 09:52 AM
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crossup's Avatar
I'm a million miles from knowledgable on hall effect sensors but my thought is the sensor arrangement you have only works over a small motion range and while your travel shown is small its still too much so you go out of range of the sensor. I would suggest testing the sensor by wiring it to DVM so you can see how the output varies with distance and orientation. with a sensor that is designed to sense N-S it seems to me you should orient the magnet on edge so when it move one direction the N face is closest and the output decreases and S face would give an increase. Not sure how that would work when both faces are centered over the sensor.
But it seems as you have it now you are getting only half the output range.
Nov 14, 2019, 09:58 AM
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Regardless of whether you get this working or not you have obviously gotten it to the point where it CAN be made to work. PLEASE post details- which 1.7 g servo, schematic of course.
I know of at least 2 other who are trying to use that gearbox for a servo, I have heard its extremely fragile and fiddley but to me it still seem better than the alternative of using very little gear reduction as other micro servos do.
Nov 15, 2019, 01:35 AM
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Hello

Please find schematic of the 8 pin chip ( CR0810-A) from 1.7g servo

Charles
Nov 15, 2019, 01:36 AM
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Quote:
Originally Posted by crossup
Regardless of whether you get this working or not you have obviously gotten it to the point where it CAN be made to work. PLEASE post details- which 1.7 g servo, schematic of course.
I know of at least 2 other who are trying to use that gearbox for a servo, I have heard its extremely fragile and fiddley but to me it still seem better than the alternative of using very little gear reduction as other micro servos do.
Yes totally agree with you the small gearbox 4mm is too fragile.
I need to use gear from 1.7g servo i think
Nov 15, 2019, 08:18 AM
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Some quick ideas for making a HK5320 lighter...
Pick of the bottom cover and forget it somewhere.
The gears are pretty good, so lets keep them but replace the axles with carbon. Screw out all the screws, and use glue or heat shrink insted. I have seen someone shave material of the upper "cover" so only the fittings for the axles remain. Pretty cool, but my argument against that is... dust. If we then replace the heavy wires we could get a 1.5g servo. The small potentiometers weigh 0.2 to 0.3g. How much of that can you save by using a Hall sensor insted?
And is there a drawback to using only the chip and not the whole servo-board?
Again, very cool idea.

An after thought... the planetary gear is pretty cool but far too small. How bout using one or two spiral"worm"gears?
Nov 15, 2019, 09:48 AM
SpinsMakeTheWorldGoRound
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This is the Hall Effect Sensor that Nick uses. Data sheet is on this page.

https://www.allegromicro.com/en/Prod...ICs/A1304.aspx

This is the magnet he is using

https://supermagnetman.com/collectio...t=540892889102

I think your problem is in the mounting of your sensor magnet. You can see how Nick does it in the photo below.
Nov 15, 2019, 09:52 AM
SpinsMakeTheWorldGoRound
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Photo
Nov 18, 2019, 05:44 PM
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Hello

I test to used a 1.7g servo for the gearbox because i dont have tools to make similar servo as Nick.

- 1.7g servo gears
- 8 pin chip CR810-A milled
- sot 23 hall effect 49e
- 3.2mm motor
- magnet from 4mm motor cutted to 1mm
Nov 18, 2019, 09:20 PM
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Great job cutting weight down, let us know how it works, maybe another video if you can.
Nov 22, 2019, 06:22 AM
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diy 500 mg based on 1.7g servo (0 min 26 sec)


you can see it works weel i just have some game on the next gear
Nov 22, 2019, 06:48 AM
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Hello Bob

Thanks for the link but freight cost for the magnet is arround 42 usd to France.

Quote:
Originally Posted by Bob Bailey
This is the Hall Effect Sensor that Nick uses. Data sheet is on this page.

https://www.allegromicro.com/en/Prod...ICs/A1304.aspx

This is the magnet he is using

https://supermagnetman.com/collectio...t=540892889102

I think your problem is in the mounting of your sensor magnet. You can see how Nick does it in the photo below.
Nov 22, 2019, 09:32 AM
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Congratulations, you have proven that the Hall sensor can replace a pot and that is huge. I'm going to apply that to the gearbox you tried as I see how to do that and given I have a machine shop to make what ever I need.
I'll post results here. My thought is a simple shaft adapter to mount the magnet on the shaft with the output arm on the magnet. Then a bracket to hold the sensor over the magnet.
I presume you used no other electronic components beyond the servo chip and Hall sensor?
Nov 28, 2019, 07:27 AM
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crossup's Avatar
Did you use the motor pinion from the supplied 4mm motor on the 3.2 ?


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