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Post by clyevo on Apr 14, 2015 2:52:30 GMT
This questions may require some knowledge of mechanical physics
1) which of the torque specification is relevant to arm lever 6dof design : peak torque or continuous torque? - i've read specification that has varying torque at certain rpm which of course depends on the load and it confuses me
2) how does the gearbox ratio increases the torque? does the 50:1 gear ratio increase torque by 50 times? for example if the motor has continuous torque of let say 4nm does it mean 50:1 gear ratio increase it to 200nm?
3) for a platform load of 120kg including bodyweight, how do i calculate the minimum required torque of a motor + gearbox for a particular length of lever. I only know that 10nm is around 1 kg and that torque = F (r sin angle)
correct me if am wrong: so for each set of motor-gear-lever must support 120kg divide by 6 motor = 20kg = 200 newtons (F) so for lever arm (r) of 1/4 meter, we would need a motor with 1/4th of the rated torque (T) needed for the specified load
but how do i put angle of rotation [T = F (r sin angle)] into calculation in relation to determining the motor torque needed?
*i am not an engineer
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Post by hexpod on Apr 14, 2015 23:49:17 GMT
This questions may require some knowledge of mechanical physics 1) which of the torque specification is relevant to arm lever 6dof design : peak torque or continuous torque? - i've read specification that has varying torque at certain rpm which of course depends on the load and it confuses me 2) how does the gearbox ratio increases the torque? does the 50:1 gear ratio increase torque by 50 times? for example if the motor has continuous torque of let say 4nm does it mean 50:1 gear ratio increase it to 200nm? 3) for a platform load of 120kg including bodyweight, how do i calculate the minimum required torque of a motor + gearbox for a particular length of lever. I only know that 10nm is around 1 kg and that torque = F (r sin angle) correct me if am wrong: so for each set of motor-gear-lever must support 120kg divide by 6 motor = 20kg = 200 newtons (F) so for lever arm (r) of 1/4 meter, we would need a motor with 1/4th of the rated torque (T) needed for the specified load but how do i put angle of rotation [T = F (r sin angle)] into calculation in relation to determining the motor torque needed? *i am not an engineer hi,
1) 6dof even without moving has to support the load. You have definitely to consider continuous torque and rated speed (not the max speed) for your calculations. peak torque will give you the ability to accelerate. 2) yes, don't forget to include gearbox efficiency in your calculations 3) this is my approximative formula: motor torque x gearbox ratio / length of lever. The result in kg I would multiply by 3 in order to get the payload with some margin for your acrobatics. ex: 2Nm/10 (conversion to kg) x100 (conversion to cm) x 40 (gear ratio) /12cm (lever) x 3 = 200kg (platform payload) i am also not an engineer :-) cheers
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Post by clyevo on Apr 15, 2015 1:00:26 GMT
3) this is my approximative formula: motor torque x gearbox ratio / length of lever. The result in kg I would multiply by 3 in order to get the payload with some margin for your acrobatics.
ex: 2Nm/10 (conversion to kg) x100 (conversion to cm) x 40 (gear ratio) /12cm (lever) x 3 = 200kg (platform payload) why multiply by 3? is this for 3 motor 3 arm 3dof? if for 6dof, i should multiply by 6 then? ex: 2Nm/10 (conversion to kg) x100 (conversion to cm) x 40 (gear ratio) /12cm (lever) x 6 = 400kg (platform payload) the 2nm will be continuous torque as rated in specification sheets?
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Post by hexpod on Apr 15, 2015 2:27:48 GMT
3) this is my approximative formula: motor torque x gearbox ratio / length of lever. The result in kg I would multiply by 3 in order to get the payload with some margin for your acrobatics.
ex: 2Nm/10 (conversion to kg) x100 (conversion to cm) x 40 (gear ratio) /12cm (lever) x 3 = 200kg (platform payload) why multiply by 3? is this for 3 motor 3 arm 3dof? if for 6dof, i should multiply by 6 then? ex: 2Nm/10 (conversion to kg) x100 (conversion to cm) x 40 (gear ratio) /12cm (lever) x 6 = 400kg (platform payload) the 2nm will be continuous torque as rated in specification sheets? 400kg would be the theoretical limit in horizontal position with perfectly balanced load. I guess you want your platform to move :-) For ex. by tilting the platform, the distribution of weight on the arms will change completely. Also your torque consumption will depends on how hard you will want to accelerate.
cheers.
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Post by clyevo on Apr 15, 2015 3:49:24 GMT
Yeah i understand that you are sayign that there has to be a margin for acceleration of movement and asymmetrical position where balance is off and one arm may take more load than the other.
So the conclusion: 1) "peak torque" is important for acceleration 2) "continuous torque" is important for holding the load at 0 movement 3) 2nm of continuous torque is suitable for my application (120kg load) with considering the need for extra torque to accelerate the movement of platform
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Post by vicpopo on Apr 29, 2015 18:30:08 GMT
You can increase the gear ratio, 60:1 is for me not big enough. If you have 15 / 20 rpm at the shaft output is enough.Your gear ratio could be 90:1 with a 4 poles motor ( 1400 rpm nominal speed). And with a bigger gear ratio you will increase a lot the torque available.
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Post by clyevo on Apr 30, 2015 7:09:54 GMT
15 rpm means it would be too slow to complete a cycle of movement especially if i plan to build high angle joint. The heim joint i am looking at has misalignment reducer which result in about 55 degrees angle compare with without misalignment reducer will only be 34 degrees angle.
So i think i ll buy a 2hp 4pole motor with 60:1 gear that will be about 23-24rpm output and plan to run this 100% motor speed on thanos board settings.
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Post by vicpopo on Apr 30, 2015 11:07:59 GMT
Hi , It's your choice ! I didn't understand quiet well what is the relation between the max speed reducer and the heim joint angle for the motion ?
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tino
Junior Member
Posts: 71
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Post by tino on Apr 30, 2015 18:36:14 GMT
15 rpm means it would be too slow to complete a cycle of movement especially if i plan to build high angle joint. The heim joint i am looking at has misalignment reducer which result in about 55 degrees angle compare with without misalignment reducer will only be 34 degrees angle. So i think i ll buy a 2hp 4pole motor with 60:1 gear that will be about 23-24rpm output and plan to run this 100% motor speed on thanos board settings. There is a bit of caveat here. Using bigger gearbox means you can have longer lever (using the same motor), which results in more platform movement without sacrificing speed. Speed is determined ultimately by the amount of torque you have, but you can have more platform motion by using bigger gearbox and longer lever. Think of small wheel vs big wheel...
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Post by clyevo on May 1, 2015 3:12:20 GMT
15 rpm means it would be too slow to complete a cycle of movement especially if i plan to build high angle joint. The heim joint i am looking at has misalignment reducer which result in about 55 degrees angle compare with without misalignment reducer will only be 34 degrees angle. So i think i ll buy a 2hp 4pole motor with 60:1 gear that will be about 23-24rpm output and plan to run this 100% motor speed on thanos board settings. There is a bit of caveat here. Using bigger gearbox means you can have longer lever (using the same motor), which results in more platform movement without sacrificing speed. Speed is determined ultimately by the amount of torque you have, but you can have more platform motion by using bigger gearbox and longer lever. Think of small wheel vs big wheel... I never though it that way, u added a new perspective, thanks. So the maximum angle and displacement of platform is not determined by how fast final rpm is. Nevertheless, the travel speed of the platform and the time taken to complete a single movement will be reduced if the rpm is lower. To complete a single one way full movement (180 degrees gear output shaft rotation), it will take 250ms for 30rpm. Eg: Let say if u loss traction the yaw movement will spin you at about 250ms. This is very fast travel of platform (u can get high G especially if the lever arm is long like 200-250mm). However if u reduce the rpm to 15, it will take 500ms to achieve this movement. I am not sure this is acceptable if you want high fidelity movement and fast platform travel especially rally racing since that is what i am interested in. Please correct me if my theory is wrong, especially the one that get to experience this practically.
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Post by vicpopo on May 1, 2015 7:29:57 GMT
I tested once at 30 rpm with 80 mm arm level , it was from far to harsh for me. But it depends of many parameters , the movement setup (smooth ) , the accelerations ramp up and down , etc ... It's the question of personal feeling and costs .What is sure is if you have too much power , you can decrease the power setup ( motor speed , etc..) if you find your sim too harsh. Look at my sim rig with motor 0,25 kW , 12 rpm(200Nm torque) , arm level 110 mm ( i assume that 0,25 kW is too low for 150kg playload , I can't mount screens on my plateform ... Waiting for occulus rift solution ) youtu.be/g88ONQXnKNQ
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Post by clyevo on May 1, 2015 11:37:54 GMT
Vicpopo - what material did you use for the platform, steering and seat holder. Is it stainless steel? how much is your payload For my experiments and tests, if you have 200kgf, in the top of the arm, your payload for a 6dof will be 200kg. Doenst matter if you are using 3 or 6 motors, it only define the dof's. If you have 30º for roll per example, in a exit of a corner, one motor for a short time, will need handle all payload. My first 6dof, i used 0,75KW a/c motor. It generate with 60:1 reduction, about 20nm torque. Using an arm of 0.15m, the maximum payload using wigh acelerations about 50hz on the VFD, and 100% on the AMc, was about 200kg. Now im building a 700kg payload 3 dof platform. I will use 3Hp motosr to handle the mass. The output torque after the reduction will be somethiung like 90nm When you talking about 6 dof, huuuuuuuuuuuge motors are welcome! You always need more torque! Trusth me! Regards how do you manage to get 700kg payload? if my setup using 2hp AC motor with 60:1 (about 2/3rd torque of yours if u using 60:1) and 250mm arm lever (about 2x of yours) how much payload can i take? Base on your model i can say mine would be able to withstand 700*2/3*1/2= 230kg only
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tino
Junior Member
Posts: 71
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Post by tino on May 1, 2015 16:52:56 GMT
I never though it that way, u added a new perspective, thanks. So the maximum angle and displacement of platform is not determined by how fast final rpm is. Nevertheless, the travel speed of the platform and the time taken to complete a single movement will be reduced if the rpm is lower. To complete a single one way full movement (180 degrees gear output shaft rotation), it will take 250ms for 30rpm. Eg: Let say if u loss traction the yaw movement will spin you at about 250ms. This is very fast travel of platform (u can get high G especially if the lever arm is long like 200-250mm). However if u reduce the rpm to 15, it will take 500ms to achieve this movement. I am not sure this is acceptable if you want high fidelity movement and fast platform travel especially rally racing since that is what i am interested in. Please correct me if my theory is wrong, especially the one that get to experience this practically. You can use this site to calculate the final speed: www.endmemo.com/physics/rpmlinear.php(refresh the site after every calculation) basically: Radius 0.1m (100 mm lever) RPM 30 ------------------ Liner velocity = 0.31416 m/s radius 0.2m (200 mm lever) RPM 15 ------------------ Linear velocity = 0.31416 m/s
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Post by vicpopo on May 1, 2015 18:26:29 GMT
Yes it's stainless steel . The total payload is near 150 kg ( just my weight is 93 kg !! )
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Post by blizzard on May 2, 2015 14:46:36 GMT
Hi all,
I follwed this thread with great interesting and I've a question to my own set up.
I'm just experimenting with a mockup in a scale of 1:3. I'm planing to build a platform with a size of 2,50x3,00m and 6DOF for a 737NG Cockpit. I've calculated a payload of about 750Kg, so one gear motor have to take a weight of 125Kg. My first 3-phase worm gear motor are able to generate a torque of 460Nm (1,1KW=1,5hp, ratio 63, 15Upm), so my possible handable max. weight of each motor is 191Kg(under the conditon the platform is horizontal).
The very interesting question is what happens if the platform is e.g. in a max lat.flexion of 45°, because then it's a inclined plane(logical) and how will be the load of the 6 motorgearaxis in different. And finally, are there an extremely situation are possible and imaginable, that in a max flex position of the platform one motor will move only or it is all the time a motion of several motors? Under the condition of my muckup I'm able to move one motor only.
The handable force of each motor is known depending of the lever(24cm) and the angle( which angel? In relation to the platform?!) and would be in my case 191Kg(angel 90°) and 110Kg(angle 10°).
If the load is greater then the motorgear are able to force, will the motor stop completely or overloaded for a short time only, but still move?
Do you have experiences?
regards
Rolf
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