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Power supply options

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by Doon1, Jan 25, 2018.

  1. Doon1

    Doon1 Member

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    I have 24 volt motors. They have 1.4 ohms of resistance so they should max out at about 18 amps. My choices are 1. Hook a pair of variable (15 volt max) power supplies in series. 2. Hook up a pair of 12 volt 400cca/26a batteries in series with a 24v/10a battery charger. I have all of these components.
    Due to the size of the chair I will be mounting the power supply/control system remotely about 4 feet from the chair. I have some space constraints so I can't use the power supplies and batteries together and it's my understanding that having a battery in parallel with the PS is important.
    I'm trying to determine if the two batteries in conjunction with the charger will be enough to provide the power for a several hour racing/flying session or will it run out of power half way through.
    Does anyone use a battery/charger combo to run their chair?
  2. Javo5

    Javo5 Active Member

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    My Motion Simulator:
    2DOF, DC motor, Arduino
    18A*2=36A. In theory needs a 36A/h battery for each hour of play (108 A/h battery for 3 hours for example). But the motors not have full power always, and the batteries not have 100% efficiency
    • Like Like x 1
  3. Zed

    Zed VR Simming w/Reverb Gold Contributor

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    My Motion Simulator:
    2DOF, DC motor, JRK
    A lot of the 6 dof guys run battery/power supply hybrid systems due to the higher power requirements. Might have a look at those threads.
  4. Doon1

    Doon1 Member

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    So If I'm pumping in 10A/h with a battery charger then (in a perfect world) I would get an hour of gaming in. Hmm...
    I've been scouring the net trying to find a good answer to undervolting the motors. I have those 2 15.3v/40a power supplies. How much performance loos would be experienced running the motors at that lower voltage. I know speed would be reduced but there are several conflicting answers on whether or not the torque would drop as well. Doing the math, the amp draw would increase from 17A to 27A (37%) at 15 volts. Not sure if the motors can handle the level of increase or if the torque rating of the motor would be less. Darn 24 volt motors...
  5. RandomCoder

    RandomCoder Active Member Gold Contributor

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    Why do you think the amps would increase?
    If you use a lower voltage your current will also be lower as will the power drawn by the motor and the torque output of the motor.
    Voltage and current are directly proportional to power.
  6. Doon1

    Doon1 Member

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    A day's worth of reading. It seems that Ohm's law kinda goes out the window when dealing with motors. All that measuring the resistance of the windings do for you is give an indication of the startup current with no additional load. But even that is only an indication as you have to factor in a bunch of other stuff.
    I was a mechanic for several years and I always knew that low battery voltage would burn up the starter because the current would increase. It always seemed counter intuitive. Now I get it.
  7. RandomCoder

    RandomCoder Active Member Gold Contributor

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    Ahh I see where you are coming from now!
    The problem with motors is that because of the windings you are no longer able to measure pure resistance and apply this to straight forward ohms law. That's because coils create an inductance.
    Therefore a motors resistance is actually referred to as impedance.

    I'm more familiar with working with AC supplies but this still holds true for DC when you are dealing with coils.
    • Informative Informative x 1
  8. Doon1

    Doon1 Member

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    So I found the gearbox info in an archived electrocraft catalogue.
    It's the R683-A28 box. still haven't found the servo info. I pretty sure it's made by Reliance Electric. All of their E660 servos (motors) are 90 volt though.
    I mounted the motor to a metal plate and mounted the plate on a vise. Using the 2 12 volt power supplies hooked in series I did a stall torque test on it for a half a second. it maxed out the power supply's 4o Amp capability. That's a lot of amps. I may crank up the voltage to 30 volts to see if the amps are within the capability of the power supplies. I tried to hook a torque wrench to it but it kept loosening the bolt that I had torqued down to 50 lbs/ft. so I need to figure out another way of checking torque. Here's the gearbox specs in case anyone might need it in the future.

    Attached Files:

    Last edited: Jan 29, 2018
  9. Doon1

    Doon1 Member

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    I'm forging ahead without firm motor data using data from similar motor specs from Motion Dynamics. Can anyone give me some feedback on the pitch force and torque numbers? Are they within the acceptable range?

    Attached Files:

  10. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
    3DOF, DC motor, JRK
    I am not sure I can properly envisage the design you intend from your SimCalc inputs. Can you please supply a picture of the intended design and anticipated user/rig/peripheral load, as it seems to me you plan a compact design with a very high CTC and I suspect inadequate torque may be an issue.
  11. Doon1

    Doon1 Member

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    Yes it is a compact full motion seat. The intended load is about 250 lbs. I have the motors tucked under the seat. the CTC is 75 mm. The connecting rods are 160 mm long. The connection point on the seat is directly above the actuator arm when it is centered, forming a 90 degree angle, and are 200 mm behind and to the sides of the universal joint. the travel of the actuator arms is 45 degrees in each direction resulting in a 15 degree pitch of the seat in each direction. If need be I can move the motors outward and back and I can shorted the actuator arms. I wish to maintain as much travel as possible as this will primarily be used for flight simulators.
    Here is a picture of the base unit and test motor bracket. I have fabricated the motor bracket 4 times to make it strong enough while staying lightweight. Now I just have get the measurements for optimum motor placement.

    Attached Files:

  12. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
    3DOF, DC motor, JRK
    Disregarding mechanical loss, it will be Mass (kg) x Acceleration (m/s) = F (N). It takes 9.8N per kg to counteract gravity.
  13. Doon1

    Doon1 Member

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    I've been taking some pictures along the way that might help you better understand the CAD drawing. It was tough to hold and take the pics so I just laid it on the ground. The motors will be mounted to the chair. The batteries, PS, and controller will be mounted in a separate box remotely.

    Attached Files: