[chbot] Discrete servos

[Richard Jones]

Back in my Philips CCTV days for Pan, Tilt, Zoom and Focus control I got
the motor driver electronics down to a single IC per channel. L272 for Zoom
and Focus, and L6202 for Pan and Tilt. These devices might be worth a look
as they interface nicely to port pins and are large enough for us to see :-)

Richard Jones

On Thu, Dec 1, 2016 at 2:48 PM, Geoff <sdfgeoff at gmail.com> wrote:

> Several things:
>
> 1) Smart servos have very good/smooth motion control:
> http://www.robotshop.com/en/smart-servo-motors.html
> I've used the DS101, and know some guys who used some dynamixels for
> holding a several kg camera on a robot arm.
> 2) Some hobby servos do have a lot of torque, but you'll pay for it:
> https://hobbyking.com/en_us/jr-ds8911-high-torque-
> digital-servo-with-metal-gears-and-heatsink-25-0kg-0-19sec-69g.html
> 3) On an agricultural robot <https://www.youtube.com/watch?v=RJ8BJNaI8bA>,
> we needed to steer some wheels in contact with the ground. We used some
> windscreen wiper motors, a feedback pot and these drivers:
> http://www.robotshop.com/en/30a-5-30v-single-brushed-dc-motor-driver.html
>
> One thing to consider is heat. If you're not at zero load when holding
> position, things will get hot. One final year project used some smart
> servo's at ~30% of their rated torque only to find that after holding a
> camera for more than a few minutes they would enter thermal shutdown.
>
> Specs about speed/precision etc would be good.
>
> Geoff
>
>
> On Thu, Dec 1, 2016 at 1:57 PM, Andrew Errington <erringtona at gmail.com>
> wrote:
>
>> Some metal-geared RC servos have a /lot/ of torque.  Are you sure an RC
>> servo won't work?
>>
>> Andrew
>>
>> On 1 December 2016 at 09:50, Charles Manning <cdhmanning at gmail.com>
>> wrote:
>>
>>> A couple of stepper motors out of old printers or something like that
>>> would do it.
>>>
>>>
>>> On Thu, Dec 1, 2016 at 1:29 PM, Mark Atherton <markaren1 at xtra.co.nz>
>>> wrote:
>>>
>>>> More info about the load please.
>>>>
>>>> Size, weight, expected rotational velocity, supply voltage, acceptable
>>>> control interfaces...
>>>>
>>>> -Mark
>>>>
>>>> On 1/12/2016 12:52 PM, Robin Gilks wrote:
>>>>
>>>>> Greetings all
>>>>>
>>>>> As usual, I'm building something and I can't seem to find what I want
>>>>> off
>>>>> the shelf. Think pan head for CCTV system.
>>>>>
>>>>> I can get really cheap ones from AliExpress but they are just about all
>>>>> Pelco-D controlled which allows pan direction and speed and not actual
>>>>> proportional control. They are also very slow, taking some 20-30
>>>>> seconds
>>>>> for their full range of movement.
>>>>>
>>>>> A standard rc servo isn't going to be up to the job although the API
>>>>> (pulse position) would suit, I'm thinking 12v or 24v DC motor,
>>>>> H-bridge,
>>>>> gearing, feedback pot and control circuitry. Its the last where I can't
>>>>> get it off the shelf as the industry standard M51660L is 5v only.
>>>>>
>>>>> Any ideas what would be best to start from such that the mechanics can
>>>>> be
>>>>> easily adapted with some sort of discrete controller for the
>>>>> proportional
>>>>> bit?
>>>>>
>>>>> Thanks
>>>>>
>>>>>
>>>>
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>>
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>
>
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