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Rig design overloads motor?

Discussion in 'Motor actuators and drivers' started by FlyingColander, Dec 14, 2013.

  1. FlyingColander

    FlyingColander Member

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    I have a highly modded RnR. The base has been widened. The roll arms have been lengthened and reinforced. I'm now trying to upgrade the old pneumatic pistons with DC motors and Jerks.

    [​IMG]

    The motor is a Model ZY7712, 12 volt, 200 watts running off a 40 amp power supply.

    [​IMG]

    The motor arm is 25cm long. The push rod is 36cm long.

    The chair is well balanced and rolls left or right with little effort when pushed.

    However, when the motor is controlled by mouse under the Pololu utility, it can't seem to roll the chair any where near its full range. When a passenger is seated in the simulator, the motor just twitches a few degrees port and starboard. The motors need to move a 100kg.

    As soon as I disconnect the levers from any load, they move fast and crisply.

    The pitch motor looks like this:

    [​IMG]

    This motor is mounted underneath the roll arm of the frame. I suspect this one in particular is underpowered as the pitch mechanics of the chair are tougher than the roll.

    Are these motors, or design, inappropriate for a RnR type simulator? Suggestions?

    Cheers,

    Flying Colander

    Attached Files:

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    Last edited: Dec 14, 2013
  2. Ads Master

    Ads Master

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  3. RufusDufus

    RufusDufus Well-Known Member

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    Hi, I would suggest your lever arm (the one wrapped in yellow/black tape) is way too long. The longer this arm the greater the torque needed from the motor. Typical designs use lever arms around 50mm to 75mm. The torque on the motor is: T = radius x Force

    So in your case the radius is 5 times longer than say a 50mm lever design which is requiring 5x torque from the motor.

    The shorter the lever arm the easier the motor has to work (and the cooler your H-Bridge will be) however the downside is the smaller the lever arm the less movement you will get. You can get around this if you really want to but the designs generally start to get a bit different - I use a rope/pulley setup that has an "effective" lever arm of about 20mm, the motors have no problem moving the seat and I have 200mm overall movement.

    Personally I have only ever built the one sim so maybe some members that have experience with more than one can confirm this for us.
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  4. eaorobbie

    eaorobbie Well-Known Member Staff Member SimTools Developer Gold Contributor

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    My Motion Simulator:
    2DOF, DC motor, JRK, SimforceGT, 6DOF
    Agree on the size of the levers, but in turn, need to know what setting you are using in the Jrk, as in PID and Motor Tab.
    Basically are the motors running flat out, have you maxed the values yet.

    I would be trying to run at 600 duty cycle and 600 acceleration and have the amps set at unlimited. Then I would slowly increase the P value in the PID Tab.
    Before giving up on these motors , try tuning them in the pololu software.
  5. bsft

    bsft

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    As its for flight slow the speed but keep the power up.
    Max Duty Cycle at say 200, and Max accell at 600. This should slow the motor but give more power.
    Try PID of 2/2 0/3 1/1.
  6. FlyingColander

    FlyingColander Member

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    I cut the lever arm down on the roll axis to 8 cm. In the Pololu utility I can roll -- with a passenger seated -- to any degree and hold that position for however long . Problem solved.

    Pitch is killing me. The nose up / nose down axis is proving much harder to solve. The previous owner used two pneumatic pistons on either side to power the pitch.

    RnR extended base 101_0588b.jpg

    I tried cutting down the lever arm on the pitch motor but no luck. Even using the eaorobbie's and bsft's PID & Motor settings the movement was weak and position couldn't be held. This being a flight rig holding a angle trumps the quick up and down bumps and vibrations one needs to simulate while driving. Imagine a steep bank in an airplane. Basically the rig needs to lean and hold steady which challenges the motor differently.

    My next experiment is using two motors to push and pull the pitch. One motor mounted on each side of the roll arm gimbal but acting as one.

    RnR reinforced arm 101_0589b.jpg


    My questions are these:

    1) What sort of geometry should I be aware of as I mount the motors? This is the old set up.

    [​IMG]

    Motor lever and push rod must be at 90 degrees to one another. Check.
    What about the hard point? Should it be behind the seat? More towards the passenger's knees?
    Just not sure of the mechanics and best leverage for the setup.

    2) How do I wire two motors and two Jrks to operate in tandem?

    Do I go through the LEARN procedure in the Pololu utility for one motor and then type in the same values for the 2nd motor? Will this work? Ideas?

    Cheers,

    Flying Colander

    Attached Files:

  7. eaorobbie

    eaorobbie Well-Known Member Staff Member SimTools Developer Gold Contributor

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    My Motion Simulator:
    2DOF, DC motor, JRK, SimforceGT, 6DOF
    Have you thought about using a chain drive system in order to increase the torque of the motors , even a 2:1 setup will nearly increase the torque by double.
    @value1 shows a good design on his joyrider , simular weight and movements involved.
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  8. FlyingColander

    FlyingColander Member

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  9. eaorobbie

    eaorobbie Well-Known Member Staff Member SimTools Developer Gold Contributor

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    My Motion Simulator:
    2DOF, DC motor, JRK, SimforceGT, 6DOF
    Have you got a friend that can help, or just give it a go on some scrap. ?
  10. value1

    value1 Nerd Staff Member Moderator SimAxe Beta Tester SimTools Developer Gold Contributor

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    My Motion Simulator:
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    It's not that difficult with nowadays welding machines! I took a 1 day course where we joined some scrap and then I started with my sim. Try a MIG welding machine with a endless wire - no magic really :)
    :grin Yes, I'm an actor now. I don't have a Walk of Fame star though :D
  11. FlyingColander

    FlyingColander Member

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    Thanks for all the feedback, fellows. Circumstances, unfortunately, don't allow for sparks and welding fumes.

    Any other ideas? Doesn't seem to be any enthusiasm for a tandem pitch motors. That's probably the best I can do given my skill set, tools and situation.

    Happy holidays all.

    Flying Colander
  12. eaorobbie

    eaorobbie Well-Known Member Staff Member SimTools Developer Gold Contributor

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    My Motion Simulator:
    2DOF, DC motor, JRK, SimforceGT, 6DOF
    Not sure if the two motors will work together, another one I have actually seen is two wipers joined together with bike chain moving one cog, both motors were wired to the same controller.
    Another option might be to use wire and a pulley setup, like @RufusDufus shows , mostly build from wood. May be an option, I and @bsft and in the middle of developing our own linear 12v/24v actuators that would work perfectly on what you have described. Early next year I hope to bring some more light on them, funds are the issue, once I get Christmas out the way I can start the build.
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  13. RufusDufus

    RufusDufus Well-Known Member

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    Keep thinking, more than one way to solve the problem... If you like the chain and gear approach but not interested in welding, what about using rope and pulleys. You may be surprised how strong a pulley made by gluing three discs of MDF wood sheets (or plywood, etc) together can be - one smaller disc in between two larger discs - and there are plenty of ropes available that will hold up to the job.

    example.JPG
    I am sure there are plenty of other ways to move you sim as well - get creative, do some experiments :grin

    (Edit: That's funny @eaorobbie had a similar thought while I was typing)
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  14. FlyingColander

    FlyingColander Member

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    Thanks for the brainstorming.

    eaorobbie: Looking forward to your collaboration with bsft for a DIY actuator.

    I actually tried wiring two motors into the one Pololu 12v Jrk controller.

    DON'T DO IT!

    At least don't do it the way I did. The motors moved in unison for ten seconds and then the very annoyed Jrk folded its arms and refused to play anymore. I thought I had murdered a $100 chip but the Jrk is a tough little piece of kit. It came back to life after I reset all settings to DEFAULT under the File Tab in the Pololu Utility. Remember the Jrk does not have any over-volting protection of any kind, it only has reverse-voltage protection. This comes straight from the Pololu Help Desk.

    I'm still curious if anyone else has figured a way to manage this without a metaphorical shower of sparks.

    Rufus thanks for the pulley diagram. A picture truly is worth a thousand words. This'll be my fall back solution.

    Now everyone go home and spend the Holidays with your families!

    Cheers,

    Flying Colander
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  15. eaorobbie

    eaorobbie Well-Known Member Staff Member SimTools Developer Gold Contributor

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    My Motion Simulator:
    2DOF, DC motor, JRK, SimforceGT, 6DOF
    Sounds like the draw is two large, are you running a dc battery in parallel with the psu as when the motors go into a free spin as in sim pitches down the motors will feed back a current like a generator, specially if its a big movement and if it has now where to go , like dissipating into a battery it will over heat the Jrk prematurely.
    My self I would either look at a lever that multiply the torque or even a cog or two another recent sim here shows this well, to me he should just about double the torque range of the motor with the use of two gears.
    But in all the pulley idea I like the most and feel it will bring the best success,
    Early next year I will be starting my linear actuator build, crossing my fingers it will be the answer to remodelling stuff like you have and should be easy enough for most to build.
  16. FlyingColander

    FlyingColander Member

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    I think you're spot on. I am learning the hard way about dc motors being dc generators too! Luckily, Jrks are built tough.

    I pinched the fan belt off my drill press and made some crude V-channel pulley wheels out of wood. Now I have to figure a way of attaching the biggest one to the point of Pitch. Will report back. At this point I'm trying to figure out the mechanics of it.

    FC