Rotating Chair Bearings

  • Thread starter dmend
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  • #1
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Main Question or Discussion Point

Hello Everyone,

I'm new to your forum and have a personal project that I need some help with. I'm not an engineering student; just a back-yard hack with a welder and grinding wheel. My project is making a chair seat with an electric motor so it rotates 1 rpm and stops. The mechanical issue I'm dealing with now is reducing the resistance produced by the seat when it is loaded. For a 200 lb person on the chair it takes 15 lbs-ft with thrust bearings installed.

Through gearing I can reduce the 15 lbs-ft to 5 lbs-ft, but I'm challenged finding a used small DC stepper motor with that power. A new motor at $350 plus is not in the budget. Even using a compound gear set-up to reduce torque I'm having a hard time finding the right motor.

So, my thinking is to reduce the resistance. I replaced the thrust bearing with a tapered roller bearing and it took up to 35 lbs-ft to rotate the loaded seat.

Chair Description:
The chair is actually a boat seat. A steel, pedestal base that supports an aluminum vertical post (1-3/4" OD). The seat base has a 3/4" steel shaft that inserts into the top of the vertical post. The vertical post does have a resin-based insert to accept the 3/4" shaft. The bearings set between top of the aluminum post and the seat base.

The drive system will be 1/4" ANSI #25 roller chain and roller chain sprockets.

Can anyone suggest a way to reduce the friction (other then using a lighter person in the seat)?

Thank-you,
dmend
 

Answers and Replies

  • #3
Jasongreat
I'm no engineer either but I have a few thought that may help.

If you could make the seat post and bearing assembly air tight, you could use an air pump to counteract the weight of the person. Even if the person was 500lbs the bearing would only ever have the friction of say a 5 lb person, but then you would add a little friction from the seals. Or if the seat will always have the same load, to get rid of the ease of adjustability, you could use grease to build the pressure, it would be easier to seal grease than air in a moveable assembly but it would be a lot messier and not as easy to adjust. The downside to that method would be the precision needed to get it sufficiently sealed up, since you didnt mention a lathe or a mill in your tool list. You could even probably rig it up with no bearing and just let it spin on a cushion of air or grease, as far as that goes, it would probably be pretty easy to change out the seat mounting pipe for an air shock and mount the seat to the shocks shaft along with a stop at which height you want so it wouldnt raise up when you stood up.

If it isnt that important to have the precision of a stepper motor, you could always go with an automobile starter, found used and cheap in a junk yard. Plenty powerful enough I would think. Sometimes there are used mill powerfeed units for sell on ebay, which I figure could be adapted with a little work.

Hope I helped.
 

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