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Dec 16, 2019, 09:15 AM
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crossup's Avatar
Thanks Martin, thats a bigger help than I expected because without putting much real thought into it I foresaw it taking two simultaneous equations. Now I see my thought was simplistic, I would have never come up with the star configuration nor the method to calculate the values, bravo.
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Dec 16, 2019, 09:25 AM
First joined Sep 2001
Working good on my end, quite happy. No reg, voltage is to low for sensor.
Dec 16, 2019, 11:35 AM
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crossup's Avatar
Picture of your setup(mechanical) please. As I feared I've likely damaged something electronically despite how robust these things are.
Dec 16, 2019, 03:33 PM
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Thread OP
CR0810_A isn't a MCU ? and need to be flashed?

Quote:
Originally Posted by crossup
US source so no customs(they opened my package from Solarbotics) and should be a couple days faster within the US.

https://www.robotshop.com/en/3vdc-38...8aAiCdEALw_wcB

Another find, 3.4mm stepper motor/gearbox. Looks like a good candidate for retract servo use as its very slow at 12RPM but that is still only 1.25 sec to 90 deg. and pretty strong. Seems to also be available with a brushed motor. Perhaps worth the weight if a small quantity retailer can be found. I'm thinking it might work out as true direct drive solution for retracts- mount the LG on an extension of the output. So no mechanism, linkage etc. just a hall sensor/magnet
https://www.alibaba.com/product-deta...3cef26c0t98Io8

CR0810-A source. There are several listed on Alibaba but this one has both a proper picture and description as driver IC
https://bestway-ic.en.alibaba.com/pr..._CR0810_A.html

This looks pretty legit too:
https://www.aliexpress.com/item/4000...739b7f8eBjifxV
Dec 16, 2019, 04:34 PM
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crossup's Avatar
Maulionc,
All info I've found says its a motor driver IC. Have not seen any which can be flashed, not to say they dont exist.
Dec 16, 2019, 05:06 PM
First joined Sep 2001
Quote:
Originally Posted by crossup
Picture of your setup(mechanical) please. As I feared I've likely damaged something electronically despite how robust these things are.
Pics soon.

Quote:
Originally Posted by crossup
Maulionc,
All info I've found says its a motor driver IC.
"Motor driver IC". I'm not so sure about that.
Edit: The typical "motor driver IC" seem to have a forward and reverse input and need a micro controller. Servos with "motor driver IC" seem to have 2 x IC.
Last edited by BlRDMAN; Dec 16, 2019 at 05:18 PM.
Dec 16, 2019, 05:50 PM
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crossup's Avatar
Birdman, I guess if you obtain a datasheet then all will be know. But the fact is as I stated it, every reference I have seen that I gave credence to said " motor driver IC" and mentioned typical use as RC servo. This may be false info or it maybe a simplistic description but
Dec 16, 2019, 06:11 PM
First joined Sep 2001
Yeah, I hear ya. But to drive a pager motor for example does not require feedback like a servo. Very different requirements.

Out of many many many IC I've looked at they all had forward and reverse "inputs", bar one that had a feedback pin.
Dec 16, 2019, 08:54 PM
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crossup's Avatar
Birdman,

First off, I bow to your superior electronic knowledge- being serious here. I have a LOT to learn but I'm getting into the nuts and bolts more everyday, so definitely trying to learn. I've been looking at a lot of driver chips and all the serious sub-industrial level stuff is not only programmable but has lot of power under the hood. But I also see PWM controlled drivers that lack only the feedback that are very basic architectures . I do know feedback can be one of the more computation intensive parts of driving a servo. On the other hand, that function was handled by discrete transistors in fairly simple analog circuits back in the day. I also know some analog circuits can be emulate digitally easily and some are bitches, so I'm not comparing the simplicity of one versus the other just suggesting it may not be that hard without a programmable MCU.

My take at this point is the CR0810-A is a purpose designed chip which is simplified by eliminating the ability to be programmed for multiple parameters- simplified like fixed gain, no temp compensation, has voltage dependencies, little error handling and who knows what other compromises. I hope you can get that datasheet. Perhaps you can say where you are trying so we can try others to make sure this happens if possible.
Dec 17, 2019, 02:35 AM
First joined Sep 2001
Electronics is just another hobby for me and on the grand scale of it my knowledge is limited, like you always learning.

Going to try worm gear on motor, if it works out should make a compact servo.

Like to hear peoples thoughts on servo arm travel. The small bricks have 4mm each way, I'm thinking 3 (@ 6.34mm) would be enough for the smallest servos, the control horn on a tiny model is not going to be very long. Good resolution and slop free linkages being more important.
Last edited by BlRDMAN; Dec 17, 2019 at 02:42 AM.
Dec 17, 2019, 07:20 AM
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crossup's Avatar
Birdman, can you post a picture of your working gearbox servo? I am looking for reasons why my setup is jittery. While I certainly can not eliminate damage to my two components, to me the fact it works at all says maybe its another factor. No point in me making another with the same issue just to test the theory when you have a properly working unit.
Dec 17, 2019, 11:56 PM
SpinsMakeTheWorldGoRound
Bob Bailey's Avatar
Instructions for adapting gearbox to smaller motor.

Photo A : Adaptor.

1 Machine a rod for the mold. It can be teflon, delrin, or aluminum. Center drill it to the motor shaft size you are using. Turn down the outside of rod to 2.70 max. 2.65 min.

2 The mold should fit on motor like this.

3 Cut a piece of 1/8 heat shrink and stretch open one end of it with needle nose, so it will fit over motor. I use 1/8” clear pvc it is lighter and stiffer than the polyfin.

4 Smear a small amount of Vaseline on mold for easy removal. Put heat shrink on mold and shrink.

5 Remove adaptor and trim to desired length.

Photo B : Motor modifications.

This is the motor I am currently using. Unfortunately it has a .6mm shaft, but it is fairly easy to put the pinion gear on it and you can make it lighter than any other motor.

https://www.ebay.com/itm/10PCS-DC-1-....c100047.m2108


0 Stock motor.

1 Remove motor mount. The motor is glued to this mount, take an exacto knife and put it between mount and motor. Push down until you feel the glue crack lose. Do the same on the other side. Remove motor and scrape off glue.

2 Take 2 pairs of pliers and grab eccentric weights. Twist and pull. One of the weights will come off.

3 Chuck motor shaft in a battery drill, grab the other weight with pliers. Twist and pull.

4 Remove solder pads.

5 Chuck rear shaft in battery drill to keep shaft from spinning and cut off front shaft flush with the bushing.

6 Heat and stretch a piece of 1/16 heat shrink so it is a snug fit on the rear shaft. This is to keep the commuter and brushes in place..

7 File around the front corner of motor until you see a faint line all the way around. Clean fillings off of motor with blue tack. Grab front bushing with pliers. Twist and pull. This bushing is not necessary, the sun and planetary gears will do the same job, just like a ball bearing. This also allows us to glue the sun gear to the shaft with out worrying about getting glue in this bushing.

Photo C : Gearbox

1 Heat stretch a pice of 1/16 heat shrink to fit inside the magnet. Slide heat shrink over out put shaft of gear box and push magnet down onto shaft. This should be done before removing gear box from motor. If not and you accidently push the shaft in the planetary gears will come spilling out. There should be a small amount of in and out play on the shaft if every thing is right. Trim off excess heat shrink.

2 Pull the motor out of gear assembly. Do not turn assembly up side down, gears will fall out. To remove the sun gear, take a piece of 1/16 heat shrink it over a 1.3 mm metal shaft. Remove the shaft and use this heat shrink as a holder for the sun gear and to keep it clean. The sun gear is teeny tiny and hard to handle. Put heat shrink over sun gear and remove from motor shaft.

3 Smear a thin layer of super glue on output shaft of the new motor. Hold with shaft down and allow to cure. Test fit sun gear. If it has a lot of play apply another layer of glue. If it is too tight scrape off glue and try again. If there is little or no play, apply a little more super glue and push sun gear on to shaft. Remove heat shrink holder when cured.

4 push the motor inside the adaptor. Push the gear box carefully in side the adaptor. There should be a slight amount of in and out play on both the motor and gear box shafts. You can push in carefully on the rear shaft of the motor to adjust this. Parts inside the red circle are not used.

5 Chuck rear shaft in battery drill and cutoff shaft with dremmel tool.

Finished weight should be around .31 grams.
Last edited by Bob Bailey; Dec 18, 2019 at 05:08 AM.
Dec 18, 2019, 12:25 AM
SpinsMakeTheWorldGoRound
Bob Bailey's Avatar
Quote:
Originally Posted by BlRDMAN

Going to try worm gear on motor, if it works out should make a compact servo.
The motor and worm gear in that photo are longer, larger, and heavier than this planetary gear & motor. You will need a 125 tooth gear to get the same gear ratio That's going to make a pretty large servo. The planetary gear & motor is 17 mm tall. You can use that measurement for comparison with what you want to make.

It would be possible to use one stage of this gear to get a 5 to 1 reduction, attach a jack screw to the out put shaft and make a long, narrow linear servo. You would have the problems of using a hall effect sensor for linear movement instead of radial but that can be over come.

Below is a photo of the planetary gear / motor next to a 1.7 gram servo for size reference.
Dec 18, 2019, 08:33 AM
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crossup's Avatar
Nice write up Bob, thanks for sharing.

I figured out my issue with the jittery motion. Turns out my nice Hitech servo programmer/tester does not like my powersupply output. I presume there is noise on the output as running the tester off the onboard battery gives nice smooth action. Looks like I need to come up with a noise filter for the powersupply so this does not bite me again.
Dec 18, 2019, 03:55 PM
Registered User
Thread OP
Hello all

I make new test on another 1.7g servo, the weight is arround 0.68g
I use small motor with plate shape but this motor create too much noise with the CR-0810A.
I need to change the motor to a normal 3.2mm motor
2*1mm magnet radial


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