[chbot] Discrete servos

[Geoff]

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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