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Motors Moving Faster In One Direction Vs Other?

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by Richard Ortengren, Oct 29, 2022.

  1. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    Been working on my 2DOF w/ traction loss for a few months and am finally testing everything in SMC3. Everything is working very well except that on all three motors they move slightly faster (but noticeable) in one direction vs the other. Weird thing is that it's faster with clockwise movement on one motor and counter clockwise on the others. One moves faster going up and the other going down, so not a gravity/weight issue. All three motors have their own IBT2's and 12V power supplies. I read Chris Twigg's post from earlier this year https://www.xsimulator.net/community/threads/motors-faster-in-one-direction-only.16784/
    but there was not an answer that seemed to apply. Not sue if I am missing something in SMC3 or the sketch.
    Here is a link to a video of the issue:

    Here is my setup:
    Arduino uno
    (3) IBT2
    (3) 12V 50A power supplies
    (3) 50:1 GEAR RATIO, 1.5 HP, 12V 40A, Reversible Action, 44 NM Torque Motors

    Any help appreciated!
  2. Ads Master

    Ads Master

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  3. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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  4. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    Thanks for the feedback. I did use the instructions you referenced to determine placement of the uni joint. However, I did not position the joint high enough, thanks for your suggestion. I will move the joint and try putting a load in the seat while testing in SMC3.
  5. Gadget999

    Gadget999 Well-Known Member

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    My Motion Simulator:
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    Swap the wires from the ibt2 to the motor and also the direction pin

    Is it now slower on the other direction ?

    It could be the ibt2 is the problem
  6. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    OK, I will try that once I'm done WELDING. It's on the table undergoing surgery right at the moment. I'm moving the U-joint up to the very top per noorbeasts suggestion. I do have a bag full of half a dozen IBT2's handy... I had trouble with 2 out of 3 at the beginning. If there's a better motor controller I'm all ears.
  7. Gadget999

    Gadget999 Well-Known Member

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    You can use 2x ibt2 together so they share the current

    Check out my latest build, i use a different dc motor driver
  8. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    Wow, that looks beefy. 100Amp, where did you procure them? Do you have a part number? Thanks.
  9. Gadget999

    Gadget999 Well-Known Member

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    Ebay iirc
  10. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    I relocated the uni joint directly under the seat per noorbeast suggestion. I also welded additional supports to the motor brackets to reduce some flexing and mechanical slop. I removed the motor from the rig and tested it on battery alone and it rotates at 50 rpm in both directions while unloaded. I then installed a second IBT2 in parallel on one motor per Gadget999 suggestion. The end result was the the same. Slower while lifting. The traction loss motor has the same speed in either direction, thus I think it is a mass issue as noorbeast suspected. I am going to try to add weight to the seat to simulate the rider or at least counterbalance to see if it goes away. Will post once complete.
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  11. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    I counterweighted the rig with 90lb in the drivers seat and the motor speed equalized in both directions. I see now that a heavy frame rig with knee located motors is very sensitive to proper balance. Perhaps more powerful motors will reduce this sensitivity, I am concerned that when kids or my wife use the rig it will be out of balance. If anyone has suggestions on the appropriate course of action I would appreciate it.
  12. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Lightening the top frame structure would likely help (I use aluminum), as it is not just the mass of the frame but also reversing the momentum of that mass quickly.

    Other options for consideration would be repositioning the motors somewhere near the feet to give greater inherent design leverage (or shoulder mount), or converting to a seat shaker rather than full frame design.
  13. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    Thank you for your suggestions. I am very much considering them, but I was hoping the knee position with full frame design would work with the motors I selected. In using SimCalc, on the first tab it suggests that my current motors, levers and positioning are good for 677 N of force. On tab 2 it indicates with my dimensions put in for the knee motors, I should achieve a Pitch force of ~1300 N. I attached screen shots. In your opinion, is this not enough force for the knee motor position given that the frame, wheel, pedals and driver load is approximately 125 Kilos? I also attached my motor specs. I would appreciate any feedback. Thank you.
    upload_2022-11-6_17-45-21.png
    upload_2022-11-6_17-44-41.png
    upload_2022-11-6_17-46-47.png
  14. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Disregarding mechanical loss, to know what Newtons it will take to move something it will be Mass (kg) x Acceleration (m/s) = F (N). So to move 100kg at 0.7 m/s needs 70 N. It takes 9.8N per kg to counteract gravity. Keep in mind there is significant mechanical loss in things like the gearbox, depending on the ratio you may want to allow between 10% to 50% loss for worm gears and the greater the gear ratio the higher the % loss is: http://www.meadinfo.org/2008/11/gear-efficiency-spur-helical-bevel-worm.html
  15. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    Hi Gadget999, I purchased 3 of the 100A controllers at your suggestion and should have them in 2 weeks. From the pictures of the product I see the pinout is written in Chinese, did yours come with instructions in English? Also can you recommend how to wire them for a 3 motor 2 DOF with traction loss? I know they each can control 2 motors, so I bought a spare, or I could use all three and lighten the load on the controller. Right now my Arduino sketch is set up for Mode 2 because of the IBT2. I will need to change that to Mode 1, is that correct? Thank you for your recommendation and assistance.
  16. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    Thank you for the link. After reading, I am wondering if the efficiency (or inefficiency) is already taken into consideration in the motor output rating. Any type of gear reduction loses energy in making the transfer to the output shaft. This makes sense to me, but it would not make sense to sell motors based on the input torque of the electric motor to the gear reduction and not the output shaft. Do you know if this a common marketing ploy of gear motor manufacturers? I would expect the N rating of the gear motor to be at the output shaft, otherwise engineers would have to back into a lot of calculations to spec gear motors for their projects!
  17. Gadget999

    Gadget999 Well-Known Member

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    The advert shows the wiring pins
    It needs 2 direction pins and a pwm pin

    Attached Files:

  18. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    Thanks! So for this 100A controller, do you agree that this would be the appropriate wiring diagram?
    upload_2022-11-10_20-26-8.png
    Do you know what are the two unused pins Voltage and Current Detection can be used for?
  19. Gadget999

    Gadget999 Well-Known Member

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    that looks good, i don't know what the other pins are for. I don't use them.

    I suspect these pins go high if the voltage is not between 12v and 60v and the current is too high
    Last edited: Nov 11, 2022
  20. Richard Ortengren

    Richard Ortengren Florida Racing Fan Gold Contributor

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    I finally received the 100A controllers from China and installed them. I fried 2 of the 3 instantly :( I did not notice that I had my PWMax set to 255. I was messing with the SMC3 settings when trouble shooting the dual IBT2's and had raised it and forgot to change it back. The rig did center itself with the new controllers, but only for 1-2 seconds before smoke came pouring out. Makes me wonder if they truly are 100A continuous with 200A surge. My 12V LED power supply is supposed to deliver 50A and the motor supposedly only draws 40A... Anyway, I bought 3 of them, so I went for broke. I adjusted PWMax down to 20 and then went higher slowly to get a single motor working and so far it seems to work great at a PWMax of 60. I ran it in motion for 20 minutes without it even getting hot. I ordered 2 replacements and will update after I can test all three motors.

    Question, I was wondering if you think I can use both of the motor outputs of one controller to achieve a higher amp draw ceiling on a single motor? Similar to using 2 of the IBT2's. I was thinking maybe I could split the direction and pwm signals across the 6 input pins and then combine the outputs of motor 1 and 2 to a single motor? If you have any thoughts on whether this would double the capacity please let me know. Thanks.
  21. Gadget999

    Gadget999 Well-Known Member

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    I am suprised your motors are pulling that many amps with no weight on your rig

    Are your motors 1.5 hp each ?
    Are they 12v 24v or 48v ?

    My motors are 800w and have been 100% reliable unless i have wired them wrong

    Set your pid numbers to small numbers and then work up from there slowly

    It does not matter if the pwm max is 255 imo

    I dont see why you could not use 2 channels on one motor, but i am suprised that you would need to.
    Can you put a clamp meter over the motor wire and measure the actual current used.

    What pid numbers do you have ?