Thread: Wheel chair lift

So back in this post https://metalworkforums.com/f303/t20...00#post1982600 i did a test lift and lifted 56kg with a spool connected direct to the motor and now i have a combined 5:1 gearbox and 2:1 cable reduction = 10:1 and the thing would barely lift a 90kg lump, that's me. I got dragged away before i could work out what is not happening but it must be losing power somewhere in the relay box??? And it will need more spring tension as i could get the cut-out switch to work with a bit of a bump down....... teething problems.....

only got a couple of pics..

John,
how does the diameter of the test spool that lifted 56kg compare to the diameter of the spool in the current arrangement? Any difference will alter the effective reduction ratio I think.

Originally Posted by jack620

John,
how does the diameter of the test spool that lifted 56kg compare to the diameter of the spool in the current arrangement? Any difference will alter the effective reduction ratio I think.

G/day Chris, it is a little bigger in dia but with the 10:1 reduction the motor should blitz it, i will hook up the battery directly to the motor in the morning and see what happens....

Or even take some voltage readings across the components from the battery to the motor to see if you have voltage drops anywhere along the circuit. A bad connection, or high resistance on any relay contacts when under load will show as a significant voltage where any power is being lost. As I said once before, that is a very nice looking piece of work there Shed, it absolutely looks factory built, and I suspect that close examination would put it into the top end category.

Originally Posted by Ropetangler

it absolutely looks factory built, and I suspect that close examination would put it into the top end category.

Thanks Rob but i still have some problems to solve, was it Edison who said that he knew 1000 ways not to make a light globe? I could tell you a few stories about places not to put grease nipples and welding things on and then cutting them off and welding them on again a few mm away then having second thoughts and cutting off again and making a slightly different shape and welding on again......you know 3 steps forward one step backwards two steps forwards.......

So today i decided that before i do anything i will load test it then i will have some data to compare with any modifications or hopefully any improvements that i make.

So i wrapped a tie down strap around the platform beam and the folding support leg and inserted the crane scale and held the switch in the lift position while watching the kgs pulling on the gauge, the motor was just slowly chugging away and struggling and i was flicking my eyes around the lifter and tie down strap back to the gauge trying to see what was bending or slipping, yup the leg was moving up so i kept my finger on the button and at 159 kilo's the weld on the leg stop let go, cool....more weld more steel and just one more thing to add to the to do list..... i was pretty happy that the flanges on the beam didn't bend.

Shed, did you take any current readings during your test run? If so did you get anywhere near full load amp draw? Or did you find any weak spots?
I do understand what you mean when prototyping any complex device like your lift. I guess that for people familiar with and competent in software like Fusion 360 and other even more powerful packages that allow machines to be synthesised, operated and clearances, stresses and strains all to be analysed, allows them to avoid the chopping and changing that the rest of us do to even get some basic operating happening, let alone achieve long term reliability and ease of maintenance when the time comes. Keep up the great work,
Rob.

Originally Posted by Ropetangler

Shed, did you take any current readings during your test run?

Rob i had a volt and clamp meter in view but was having so much fun demolishing that i forgot to look at them

I will bomb proof that leg and re visit the lecky stuff

G/day fella's, a little more progress with this, as John Baron suggested I fitted 2 ceramic capacitors to the motor brushes but I still had problems with the DC to DC converter, I would test it on the bench hooked up to the winch motor and it seemed to work fine, resealed the box and fit it to the lifter and was only getting 12v to the motor??? Pulled it off and removed the cover checked it and wiggled all the connections and all good, lifter going up and down with 24 volts like a champion...
Put it all together and back on the lifter...yup only 12v again pulled it apart again and shortened all the wires and fitted new connectors and tested a ok again....put it all together and back on the lifter and WoooHoo 24v..... ummm oooopsie.... it stopped and let the magic smoke out of the converter.....but no genie
So I did what I always do when something breaks.....go bigger... I piffed the chinese reversing relay (tested ok but I was suss about it) and I hot glued 3 x 12v 40a relays and the remote control module into the box and wired them up with a plug for a manual switch also...so new wiring and relays and a new larger converter... Talk about a head f*c#
Tested no problemo...so far.
I cheated with the spring tension on the winch for the limit switch, as you can see in one of the pics I fiited another spring over the top of the winch and after a few adjustments i got it to open the switch at about 240 kgs.
So a bit of a new problem there ....need more spring tension there as there is more friction than I anticipated at the pivot points on the parallel arms that control the lifting arm...just a bit more mucking around i guess, the cable is rated at 290kg from memory but the cable reduction should allow for twice that so the extra load should be ok.
I weighed the lifter and it weighs a measly 80kgs. I will make a slip on roller blade to move it around.
I put 165 kgs on it and it takes between 50 and 55 seconds from bottom to top.
The amps at the 12v battery cable start at 14A and climbs to 15 - 16.5A as it gets higher, then when the linkage control is activating and lifting the load higher it pulls 26 amps... I think i need to find a way to reduce the friction there, there is a hell of a lot of leverage there.
Still a few things to do before it goes onto the car but happy to say that it does work....

I made this gizmo to be able to maneuver this lump around and to get it on and off the car, just nip up the one nut and it is held firmly. To steer it just lean it over a bit onto the side wheel and roll that end around to get the lump to point in the direction you want to go, i did a couple of laps around the workshop with no incidents or fatalities.
To get it onto the car the idea is to line it up to the towbar and just poke it in...

G/day fella's, i had to do a couple of mods to the wheelchair to get it into the car, the backrest needed to fold down and the r/h armrest also needed to be modified to allow it to be lowered otherwise the controller was a bit high when the chair is raised up.
The tow bar mounting has an axle inside there so there is no through hole for a pin to retain it so i knocked up a g-clamp to do the job.
The back tyres on the car will throw a fair bit of water stones and muck at it so I have ordered a double swag carry bag to cover it up, fingers crossed it will do the job,
Here are some pic's showing the chair mods and the folding it out sequence......
and here is vid of it doing a lift, not sure i like the sounds coming from the cable so i will just keep an eye on it and deal with it if it becomes a problem.... https://www.youtube.com/watch?v=A2K89hGruRY

That is impressive!