Motorized Revolving Chair

Discussion in 'The Projects Forum' started by dmend, Sep 11, 2010.

  1. dmend

    Thread Starter New Member

    May 11, 2010
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    Hello everyone,

    Sorry for the long posting, but the devil is often in the details and as indicated before, I am a novice in this area. In a previous thread on this project (Forward and Reverse Motor Controlls) I introduced what my project is (see project description below) and got some good direction from this community. I'm now ready to continue my project and will appreciate your expert comments on the description below. Thanks in advance....

    As time has allowed I’ve assembled the chair and settled on the gear system (roller-chain and two gears) and have determined it takes 15 foot pounds to move a 200 lb person sitting in the chair. So that appears to have been the easy part of the project.

    After converting the 15 ft lbs: = 20.337 269 28 Newton meter or
    =2880 ounce inch, or 632.1015 nM*n (milliNewton meter) I’ve searched the previously referred websites and others for a motor of this magnitude with little luck. I was hoping to find a take-out, but realize I may be buying new.

    It looks like the major components I need to acquire are the
    • Power source (ac/dc converter matched to controller and motor),
    • User control buttons and cables
    • Controller and cables,
    • Timer and Bell or buzzer device,
    • Sensors
    • Motor.

    The Motor Specs:
    • Bi-polar, Constant Voltage or Resistance Limited
    • PM permanent Magnet or Hybrid
    • 650 mN*m or equivalent

    Q1. Can anyone refer me to a source for this type of motor?


    The Controller:
    I think I’m looking for a Bi-directional DC Motor Speed Controller for a 4 wire bi-polar stepper motor.


    Q2. Can anyone refer me to a source for a bi-directional DC Motor Speed Controller for a 4 wire bi-polar stepper motor that would be appropriate for this project?


    The sensors:
    I presume the sensors will connect into the controller. I’m thinking that a small magnet placed on the gear located on the chair post will be the signal for the chair location. Then on a stationary plate will be four sensors to pick up the magnetic signal as the magnet passes over the sensors.

    Left Rotation:
    Sensor 1: a sensor to indicate a position of 315 degrees from the starting point. This will indicate the motor control to slow down.
    Sensor 2: a sensor at 350 degrees position cutting power to zero.

    Right Rotation:
    Sensor 3: a sensor to indicate a position of 315 degrees from the starting point. This will indicate the motor control to slow down.
    Sensor 4: a sensor at 350 degrees position cutting power to zero

    Q3: Based on this design the two sensors opposite of the rotation will have to be “off” as magnet passes over them. My thinking is that each set of sensors will be tied into the controller so as they are “off” at the appropriate time. Does that sound correct?

    Project Recap: Motorized Revolving Chair
    Attach a stepper motor to a chair seat to make it rotate in both directions.
    The chair needs to rotate one revolution and stop in the time period of one minute (approximately).

    Operation:
    1. The seated user presses a button to start the chair rotating to the right.
    2. The motor is delayed in starting causing a waiting period of approximately 10-15 seconds, and then the chair starts to rotate until it competes 360 degrees and then stops. Although the motor may need a slowdown period, from the user’s perspective a sudden stop is acceptable.
    3. After approximately 15 seconds a timer bell sounds indicating the end of the rotation.
    4. The seated user then presses a different button to rotate to the left (or possibly presses the same button depending on the electronics or programming to be added to the control mechanics)
    5. Again, the motor is delayed approximately 10-15 seconds, and then begins to rotate the chair to the left 360 degrees and then stops.
    6. After approximately 15 seconds a timer bell sounds indicating the end of the rotation.

    Thank you for your feedback.
    Dmend
     
  2. John P

    AAC Fanatic!

    Oct 14, 2008
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    Yes, I remember your previous thread about this project.

    What's missing here is how fast you want the chair to rotate. You could have a flea-power motor which would be geared down enough to move the chair, and it might start up and finish 1 revolution the same day. That wouldn't contradict anything you've said, but it probably isn't what you want!
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Have you selected gears yet? At 3:1 need only 5 ft lb @ about 4 RPM.
    Look at The Electronic Goldmine gear head motors like G17807.
     
    Last edited: Sep 13, 2010
  4. dmend

    Thread Starter New Member

    May 11, 2010
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    I believe the chair speed will be: 0.0421 inches per second (s=d/t 360 degrees/2.53 inches) using a 30 tooth gear from McMaster.com, product #2737T22.

    Q1: Does the speed value come into play in the motor selection or is that more relevent to controlling the motor voltage?

    McMaster also has a 10 tooth gear (273T71) with 1/4" bore which will give me the 3:1 gear ratio Bernard suggested.

    I looked at the Electronic Goldmine motor. It has a 9mm shaft. Using McMasters gears I'm limited to 1/4" or 3/8" shaft.

    Q2: The gear on the chair must have 3/4" bore. If I used a metric sized gear on the motor there could well be a problem meshing with the chain (ANSI #25 1/4" pitch)?

    Q3: You've shown me with gearing how I can use a smaller motor. Given the motor shaft requirement would it be more practical to search for a small motor with the right shaft size and work towards matching gears to get within range of my specs?
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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  6. John P

    AAC Fanatic!

    Oct 14, 2008
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    I believe the chair speed will be: 0.0421 inches per second???

    Come on pal, you need to do better than this. You can't measure the rotational speed of something in inches per second! How about "x revolutions per minute" or "y seconds for a full 360 degree rotation"?

    If it were 15 seconds per rev (4 rpm) then the input shaft would be turning at 12 rpm and the required torque would be 5 lbft or 60 lbin.

    That works out to .011 horsepower or 8.5 Watt.

    Here's a motor that looks as if it can do the job, if you can accept a 5/8" shaft:
    http://www.herbach.com/Merchant2/me...uct_Code=TM02MTR4552&Category_Code=DCGEARHEAD


    The trouble is that your torque requirement is so high that most small motors won't have gearing strong enough to drive your load. Could you install an additional gearing stage to make it higher speed and lower torque? Then you'd have more choice of inexpensive motors.

    Edit:
    I just took a look at the parts in the McMaster-Carr catalog. I think you'd be better off if you use larger diameter sprockets, which would allow you to use more powerful gearmotors, which you may need in order to get the torque you want. For example, if you used 18 and 54 tooth sprockets, you would be able to use a motor with a 5/8" shaft. I'm not going to knock myself out looking for motors, but I haven't seen any with 60 lbin torque and a 1/4" shaft.
     
    Last edited: Sep 13, 2010
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Could you give us a sketch of chair post & base fitting? Might consider bicycle chain & sprockets to give up to 5:1 reduction. If you have access to a drill-press a hub can easily be made.
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Found this for # 25 chain : ElectricScooterParts.com 80 tooth [SPR-2580 ] & 15 tooth [SPR-2515A ], giving 5.3:1 rediction, would be my choice. I would still check out bicycle parts for lower cost.
     
    Last edited: Sep 14, 2010
  9. dmend

    Thread Starter New Member

    May 11, 2010
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    Sorry to take so long to reply. Life gets in the way of doing the fun stuff.

    A)The chair needs to rotate at 1 revolution per minute +/- 5 seconds. (I thought you were asking something else)

    B) I’ve got 6” from the center of the seat post (3/4” thick) to the foot rest support. I think I can expand this to 7.5” with some reworking of the frame. I need to stick with a smaller motor.

    C) I like the idea of compound gears over the bicycle sprockets due to the size of the sprockets. I have to fabricate the motor mount so adding an extra axle is no problem. I found a formula that seems to work for me. This certainly widens my motor options.

    Gear ratio =No. of teeth on B / No of teeth on A x No. of teeth on D / No. of teeth on C
    A=drive gear on motor
    B=second drive gear
    C=first follower gear
    D=second follower gear (on chair post)
    If I’m doing this correctly:
    Ex: 15/20 X 20/30 = 2 x 1.51 = 3 = 3:1 ratio
    Thus, controlling a stepper motor at 3 rpm to make the chair rotate once.

    The Electronic Goldmine motor G17807 looks interesting, I can't decipher if it will have enough power. It’s cheap enough to get just to experiment with it. Details:Super heavy duty gearhead motor operates from 3VDC up to 18VDC. Operates in both directions and has 18" flexible leads for power connection. At 6VDC the RPM is about 15, and the current draw is 170mA. Size of motor is 1.5" in diameter x 2-7/16" long. Gearhead is 2-1/2" x 3-1/2" x 15/16" thick. Shaft is 9.5mm in diameter x 1" long "D" shaped with a threaded hole for an 8-32 screw on its end

    This looks like a workable motor with plenty of torque at 150 oz/in with a 3:1 gear ratio:
    Superior Electric Co. Slo-Syn M063-FD09, $40.00,
    Stepper Motor, 200 Steps/Rev, 150 oz/in, 1/4" shaft, 2.25V, 4.6A, 6 wire, NEMA 23, 5% accuracy. This motor cross references to the current model M063-LS09 motor with leads or the M063-CS09 with connector.

    Would you agree I have a winner here?

    Dmend
     
  10. John P

    AAC Fanatic!

    Oct 14, 2008
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    Anyone who knows me will say that I'm most likely to be motivated by a desire to see good engineering design, rather than by enjoyment of giving anyone a hard time. Nevertheless, you said, quite correctly:

    15 ft lbs: = 2880 oz in.

    Now you're proposing a "workable motor with plenty of torque at 150 oz-in with a 3:1 gear ratio". It's not clear whether that 150 oz-in applies before or after the gears, but either way, it's nowhere close to 2880. You need to gear the motor down way more, or it just won't cut it.

    As for the Electronic Goldmine motor, they don't list torque, but to my eye it just doesn't look big enough to have room for the kind of gears that it would take to deliver that kind of torque. But maybe I'm wrong on that.
     
  11. dmend

    Thread Starter New Member

    May 11, 2010
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    I see that my pea brain executed a transposing error. Not uncommon for me.

    Is it correct that if I need 15 ft-lbs to move an object, and apply a gear ratio of 3:1, then the ft-lbs will be reduced by 1/3, i.e., 15/3 = 5 ft lbs of torque?
     
  12. John P

    AAC Fanatic!

    Oct 14, 2008
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    Yes, that is perfectly correct. So the small sprocket needs 5 lb ft (you can say ft lb, but in school they'd try to get you to say lb ft, because a ft-lb is a unit of energy rather than torque).

    But 5 lb ft is still a fairly large torque. You need to be sure that the motor has the torque you need, and that the gearing between motor and output will withstand it.
     
  13. dmend

    Thread Starter New Member

    May 11, 2010
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    I can see I need to re-engineer the chair so it takes a lot less energy to rotate it. So back to the drawing board for me. I can't thank you all enough for your patience and your guidance. Hopefully, my next post will be letting you know of my success.

    Thank you again!
    dmend
     
  14. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Electronic Goldmine motor G16034 looks the same as All Electronics, DCM276 @ $ 9. with reader comments. I would og with a 5:1 gear chain reduction. Could you give us a sketch of space available under chair? Does chair have a ball bearing thrust bearing ?
     
  15. dmend

    Thread Starter New Member

    May 11, 2010
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    Well, it helps to read the directions on how to get an image onboard. I think I've attached a photo of the working space of the chair.

    Yes, I'm using the ball bearing thrust bearings. I rigged up a roller bearing and got worse results so I'm keeping with the thrust bearings.

    Also, decided on compound gearing and got the lbs-ft down to 101. Found a motor driver combo and am awaiting deliver. It should be here by Friday. I've been working on the circuitry. I've attached at test file to make sure I can attach a drawing successfully. After seeing the motor documentation I'll post a draft of the circuits.

    Thanks,
    dmend
     
  16. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Are you driving this chair from a hub or fixture at the shaft(center of chair) or are you thinking of using the drive at the outer edge of a large sprocket beneath the chair seat. This WILL affect how much torque you must use. By driving from the outer edge you gain a small amount of moment arm to overcome the inertia of the chair.

    [​IMG]
     
  17. John P

    AAC Fanatic!

    Oct 14, 2008
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    "got the lbs-ft down to 101".

    And it was 15 before?

    Point me at the wall, I think I need my head banged.

    [​IMG]
     
  18. dmend

    Thread Starter New Member

    May 11, 2010
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    Those darn typos again, s/b 101 oz-in.

    I'm using a compound gear set-up. Motor to idler gear set #1, then from idler gear set #1 to a gear on the shaft.

    I've attached a concept diagram showing the placement of the relays and timers.

    How it is to work:
    1) The user presses Start button (SPST momentary), that initiates the latching relay which powers timer #1 (delays the motor starting for 15 secs).
    2) Then, timer #1 activates timer #2 which activates the motor and allows it to run for 60 seconds and the motor stops.
    3) Mounted under the seat will be two micro switches. At the end of one chair revolution Microswitch #1 (NC) opens and depowers the latching relay. Microswitch #2(NO) closes and initiates the 555 timers. The first 555 timer delays for 15 seconds and the second 555 timer sounds the buzzer for 1 second.
    4) Next, the user switches the direction (CC/CCW) with a toggle switch.
    5)The cycle can begin begin moving the chair in opposite direction. Microswitch #2 will reopen causing the first 555 timer to reset.

    Does the placement of the timer and relay components in the diagram correctly reflect how I'd like it to work?

    Thanks,
    dmend
     
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