Project Idea Question...

If you want to say something that doesent fit anywhere else!
MAIN WEBSITE: http://www.wheelchairdriver.com

Project Idea Question...

Postby ex-Gooserider » 18 Jun 2012, 03:03

One of the things I'm running into over at the Asylum, is a fair number of equipment items that are either only operated by a foot-pedal, or which really work best with one... Among other items are the TIG welders, and the Sewing machines. In both of these cases (and probably many others) you need both hands free to use the machine. Obviously since my feet don't work, this poses a problem.

Rather than try to come up with a different solution for each machine, I have been thinking about trying to come up with a "universal pedal pusher" that I could use on any sort of equipment, possibly with some sort of configuration / adjustment needed.

What seems like a possible approach would be to have some sort of mildly spring-loaded bite mechanism driving a potentiometer or other sensor, and connecting that (presumably via an Arduino or equivalent) to some sort of high speed servo or actuator that would be mounted in an adjustable frame that can be made to hold the foot pedal.

Presumably the actuator should operate as quickly as possible, so that it tracks the movement of the bite sensor as accurately as possible, with minimal delay.

I see the following adjustments as presumably being needed -

1. Analog / digital pedal selection switch - This would control the function of the bite switch / actuator - in 'analog' the actuator would match the switch position across a semi-infinite range, in 'digital' the actuator would go from full off to full on and back as the switch passed some threshold in it's travel...

2. Holding the foot pedal locked in place. (As movement would probably mess up any other adjustments)

3. Adjusting the height of the actuator to match the pedal - presumably I would want the actuator tip just touching the pedal in it's retracted position.

4. A 'maximum travel' setting to allow the pedal to be fully depressed, without over-pressing and possibly damaging it... The controller should be able to map the full range of the bite sensor to whatever the allowed travel distance is.

Any thoughts or suggestions -

What should I use for the "pedal presser"? Some folks have suggested an actuator, others have suggested a servo - which would be better, and why, or is there another better option?

Possibly more of a challenge, any suggestions on the bite sensor? Sources? Design? Other possible control inputs? (note that the sensor should be small enough to fit under a welding helmet without interference, ditto possibly other sorts of protective gear?)

Other ideas?

ex-Gooserider
User avatar
ex-Gooserider
 
Posts: 5046
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: Project Idea Question...

Postby ex-Gooserider » 18 Jun 2012, 07:50

In looking at servos, I found the articles mentioned in my hobby servo question thread very useful...

My working assumption is that I'd want about 3-4" of pedal travel ability, with a fairly high possible force applied. The helicopter article seemed to say that 2-300 inch/ounce servos were about the best, which would give me about 10 lbs of force from a 2" arm, and 4" of travel if I had a 180* stroke...

In addition to the information, the helicopter site linked to a servo database, and I found 3 servos that had over 300 oz of force at 6.0 volts, which wouldn't be a problem for an Arduino to handle...

Search results here - http://www.servodatabase.com/servos?modulation=Digital&support=singlebearing,dualbearings,triplebearings&torque60=gt-300&speed48=lt-.24&range=gt-90

Interestingly, the specs seemed to not show a lot of difference between the three, except that the Hyperion unit was significantly lighter (not a concern, but makes me wonder what they leave out) and had a "street price" of under US$40 while the other two were around $120. The Hyperion servo only had a 140* stroke, but that would probably be enough, and the price makes up for a lot of other things...

Are the Hyperion servos any good? Is there a reason other than profit seeking why the other two units are so much more expensive?

ex-Gooserider
User avatar
ex-Gooserider
 
Posts: 5046
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: Project Idea Question...

Postby Burgerman » 18 Jun 2012, 10:36

There are hundreds of different servos. Who knows wHat is good/bad. Never saw a hyperion servo. Remember the heli guys are looking for speed, weight precision.

I generally just use cheapish RC manufacturers ones, Futaba, JR, Hi-tec etc. There are huge powerful servos available for all kinds of jobs. Including lower geared ones for sail winches etc.

All seem pretty good even some of the cheap chinese ones... Get yourself to a model plane show, look at thousands for a deal!

Up to 20kg servos here cheap! http://www.ebay.co.uk/sch/i.html?_nkw=p ... &_from=R40

But you dont want to load them to the max, so choose something that is 3x more powerful than you need.
User avatar
Burgerman
Site Admin
 
Posts: 45261
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: Project Idea Question...

Postby ex-Gooserider » 19 Jun 2012, 09:10

Burgerman wrote:There are hundreds of different servos. Who knows wHat is good/bad. Never saw a hyperion servo. Remember the heli guys are looking for speed, weight precision.

I generally just use cheapish RC manufacturers ones, Futaba, JR, Hi-tec etc. There are huge powerful servos available for all kinds of jobs. Including lower geared ones for sail winches etc.

All seem pretty good even some of the cheap chinese ones... Get yourself to a model plane show, look at thousands for a deal!

Up to 20kg servos here cheap! http://www.ebay.co.uk/sch/i.html?_nkw=p ... &_from=R40

But you dont want to load them to the max, so choose something that is 3x more powerful than you need.


Well the three choices offered were Futuba, Hitec and Hyperion, with the first two being MUCH more than the Hyperion. The database I pointed at apparently was not intended just for the Heli guys, but claimed to be a pretty exhaustive list of all the hobby grade servos, where one could compare specs and pick what was important to you... Mostly I was just wondering if the Hyperion servos had a good reputation, or if there was some reason they had so much lower prices...

At any rate, thanks for the ebay link - I might try doing a similar search on eBay US - as I figure that will be easier / cheaper for shipping if nothing else... I might also see if there are other options like CNC gear or some such...

In terms of requirements, I don't care all that much about weight and bulk, within reason. Precision isn't all that critical as long as it's reasonable, but I think speed is fairly important, for the same reason that one doesn't want delays in chair programming - the ideal would be to have the "pedal presser" be working as fast as an AB could use his foot. This probably won't be possible, but it is what I'm aiming at...

ex-Gooserider
User avatar
ex-Gooserider
 
Posts: 5046
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: Project Idea Question...

Postby Burgerman » 19 Jun 2012, 09:39

Most good servos are faster than your foot. Definitely faster than mine!

I would just get a big cheap one for that job.
User avatar
Burgerman
Site Admin
 
Posts: 45261
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: Project Idea Question...

Postby ex-Gooserider » 06 Jul 2012, 07:34

Well I was not getting on for a few days because I was seriously busy down at the Asylum...

The "Red Bull" people sponsored a contest for creative inventions that made use of a "Bullduino" board - essentially an Arduino UNO clone that was made on a big PCB shaped and printed with the Red Bull logo... I figured it was worth trying to enter as the "worst case" scenario was that I'd get a free board (worth about $25 US) and top prize was $10K and a paid trip to the "Maker Faire" in NYC - possibly the biggest maker / hacker event of its sort in the US....

My contest application was accepted, and I got my Bullduino, so I had to try and get as much built as possible by the July 3rd deadline - Can't seem to upload my contest video - even after cropping the heck out of it, and lowering the frame rate and quality settings to get it under 2mb, I'm then told that MP4's aren't allowed (any video formats that are?)

At any rate, I had to spend a lot of time in the shop on the Bridgeport, as well as a quick training session on how to do Aluminium TIG welding - result is seriously ugly welds, but seems mostly to hold together...

I also picked a SERIOUSLY gutsy servo - http://www.servodatabase.com/servo/xq-power/xq-s5040d big, but 48 kg/cm torque, 0.18seconds / 60* rotation...

I still need to finish the hardware in terms of installing the servo, switches, wiring and so on, but it is at least in semi "show & tell" condition.

I also need to get the software working on the Bullduino board....

(Minor note - not sure how global it is, for those not familiar with it, Red Bull is an "Energy Drink" - never tried the stuff myself, but I'm told it's pretty vile. I don't do carbs that I can avoid, and I'm allergic to the aspartame they sweeten the low-carb version with...)

Ex-Gooserider
User avatar
ex-Gooserider
 
Posts: 5046
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: Project Idea Question...

Postby malamar » 06 Jul 2012, 10:30

Like copy here finding it a definitive and useful classification:


My observation here in the US is that scooters tend to be used mostly by folks that are fairly mobile, and can stand / walk for at least short distances OK, but need some help for the longer distances... Typically the scooter users I see are elderly and / or very obese. Mostly they don't seem to want to modify their scooters beyond decorative things or accessories like cargo baskets. At least the bigger scooters have reasonable speeds, tolerable suspensions, lights, and so forth, so they are reasonably complete packages that don't NEED a lot of modifications... However since the user is generally semi-mobile, the fact that a scooter is less manoeuvrable isn't a big issue.

OTOH, power-chairs tend to be sold more to folks with more severe limitations where the user has very limited ability, or can't stand / walk at all, and essentially has to 'live' in the chair when not in bed - typically spinal cord injuries, and other severe handicaps - often if the mobility / rehab industry has anything to say about it, not even in good enough shape to push a manual chair.... Since the chair is our legs, we can only go where the chair can, and we must go for manoeuvrability over other factors like stability, suspension, speed, etc... Given the more severe nature of the chair user's handicaps, and the other things that were sacrificed for manoeuvrability, there is a lot more demand for modifications to make the chairs fit our needs better, especially for those of us that don't like those sacrifices...

ex-Gooserider
ex-Gooserider

Posts: 1386
Joined: Tue Feb 15, 2011 6:17 am
Location: Billerica, MA. USA
malamar
 
Posts: 495
Joined: 31 Jul 2011, 10:24
Location: Madrid Spain


Return to Anything

Who is online

Users browsing this forum: No registered users and 35 guests

 

  eXTReMe Tracker