Aluminum Weighs Less

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Aluminum Weighs Less

Postby martin007 » 03 Feb 2019, 22:22

Hello.


I´m reading (again) BM3´s construction steps.

> http://www.wheelchairdriver.com/BM-MK3- ... uction.htm


Would it be possible to replace steel with aluminum?
A lighter powerchair consumes less energy.
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Re: Aluminum Weighs Less

Postby Burgerman » 03 Feb 2019, 23:54

Yes.

You can lose about 30% of the weight with a more sensible design. Or a hacksaw. All those bolted together brackets and boiler room engineered arms and swingaways adds up!

If it was a modern japanese bike, it would have alloy wheels, frame, seat mount, swing arm, brake calipers, spacers, etc. If it was raced, it would get lighter wheels, magnesium aor titanium parts, titanium bolts axles, engine parts, and possibly carbo wheels and brakes...
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Re: Aluminum Weighs Less

Postby ex-Gooserider » 05 Feb 2019, 04:28

For the same volume of metal, aluminum is lighter... However it is weaker. Therefore unless you do a lot of engineering design work to optimize construction, you lose some of the weight reduction in order to recover strength....

Aluminum is also harder to weld and do some fabrication operations on, compared with the cost of steel...

Titanium is lighter for comparable strength, but even more expensive and difficult to work with.

In a manual chair, the frame is one of the largest pieces that contributes to the weight of the chair, so there are big advantages to taking advantage of the weight savings of titanium or aluminum (and even more recently carbon fiber) to shave every ounce off the frame as this gives a big %age weight reduction.....

So the traditional steel "E&J" transport chair can weigh on the order of 50-60lbs (~25kg) and doing light weight engineering to make the frame out of aluminum or titanium cuts that down to around 20-25lbs (~10kg) it is WELL worth the costs and effort for the better than 50% reduction in weight...

In a power chair, the frame is only a small part of the total, with the motors and batteries weighing far more... My chair weighs around 250lbs - very roughly....
100lbs of lead bricks
60 lbs of motors (guessing - I've never actually weighed them)
60 lbs of seat and other stuff including wheels, electronics, etc.
30 lbs of frame....
250lbs total....

Going to lithium chops the battery to 50lbs
can't do much about the motors... Some of the other stuff is electronics and so on, so can't do as much with that as might be possible with the frame...
So figure I redesign for light weight and cut 50% off the frame and 20% off the seating etc... I end up with

50 lbs of batteries
60 lbs of motors
40 lbs of seating and other stuff
15 lbs of frame
165lbs total...

That's a nice weight reduction, but nothing like what you get with a manual chair - so it's a lot harder to justify the effort...

ex-Gooserider
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
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Re: Aluminum Weighs Less

Postby Scooterman » 05 Feb 2019, 12:32

On my powerchair I replaced everthing from the rolling chassis up with aluminium. So armrests, backrest, centre footplate. For the seat base I used plywood but with 10 swg 6080 aluminium channel side rails. Although I'm thinking of replacing the plywood with Nylon 6 some time in the future (wood creaks)

One ironic thing with aluminium is that although it's a more expensive material than mild steel, on eBay it tends to be cheaper and more ubiquitous as it's cheaper for the seller to post out.

The chair is really nimble now, especially being re-programmed the BM's suggest r-net settings. But I'm only very lightweight myself so aluminium is strong enough for me at the guage I used, but might not strong enough for a heavier user.
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Re: Aluminum Weighs Less

Postby martin007 » 06 Feb 2019, 00:10

Do you have a photograph of your powerchair?
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Re: Aluminum Weighs Less

Postby Scooterman » 12 Feb 2019, 09:04

martin007 wrote:Do you have a photograph of your powerchair?

Blue was it's original colour https://postimg.cc/gallery/p3bcct00/
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