[chbot] Cheap Rack and pinion servos?

[Yani Dubin]

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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