[chbot] Cheap Rack and pinion servos?

[Charles Manning]

How about:
Old using a second hand stepper out of a printer + a threaded rod
($10/metre at Bunnings)?


On Wed, Apr 22, 2015 at 4:34 PM, Yani Dubin <yani.dubin at gmail.com> wrote:

> This would be a fairly close match to what I was raving about:
> http://catalog.linak.com/Linak/ENGLISH/DATASHEET/LinearActuatorLA27DataSheetEng/
> .
>
> On Wed, Apr 22, 2015 at 4:31 PM, Yani Dubin <yani.dubin at gmail.com> wrote:
>
>> Sorry, accidentally hit send.
>>
>> Was trying to paste the following in:
>>
>> "The way these actuate from memory is to rotating a toothed inner
>> cylinder, driven by the motor at one end, and gripped by a tooth (a float?)
>> at the other end - which is held rigid against an outer cylinder / housing
>> to stop it rotating with the inner cylinder, forcing it to slide along. In
>> most cases, this extends a retractable metal cylinder with a bolt in the
>> end (fixed to the load being lifted)."
>>
>> On Wed, Apr 22, 2015 at 4:28 PM, Yani Dubin <yani.dubin at gmail.com> wrote:
>>
>>> Hi Brahm,
>>>
>>>
>>> On Tue, Apr 21, 2015 at 9:16 PM, Brahm Boelee <
>>> brahmboelee84 at hotmail.co.uk> wrote:
>>>
>>>> That linearmotion site is super interesting
>>>>
>>>
>>> I have salvaged some of the hospital bed type actuators (which feature
>>> on the homepage of this site - not sure if these are the ones you are
>>> interested in).
>>>
>>> However not sure the ones I have had more than 30cm of travel. But I
>>> thought I'd mention a few things to be aware of with these, from my brief
>>> experimentation, if you are considering them.
>>>
>>> The two brands of unit I have pulled apart were based on a 24V brushed
>>> DC motor design (one was German, one Taiwanese from memory).
>>>
>>>
>>> The insulation rating in each case means you only get a 10 percent duty
>>> cycle (the name place specifies something like 2 mins on 18 mins off).
>>> Therefore they are designed for brief spurts at maximum power, and if you
>>> exceed this, you risk damaging the insulation and reducing the life of the
>>> motor.
>>>
>>> One (or both) of them had a ~40:1 reduction gearing ratio between the
>>> motor worm and the toothed actuator arm (orthogonal coupling), meaning it
>>> took quite some time to actuate (at a very rough guess, 15 seconds for 30cm
>>> - about what you might expect to gently raise/lower a patient). So not
>>> suitable for rapid movement.
>>>
>>> I evaluated the speed of the motor by cobbling together a DIY
>>> tachometer. The Dewert motor was achieving 2000rpm with the 15.7V my bench
>>> supply could provide, and sucking 200mA. So maybe 3500 rpm at rated load,
>>> and I think I saw a 50W mentioned somewhere.
>>>
>>>
>>>
>>> No idea if this is of interest, but if you want to know more about these
>>> or see one in motion, let me know and will see whether I can reassemble one
>>> :)
>>>
>>> Regards,
>>> Yani.
>>>
>>
>>
>
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