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Post by hexpod on Jan 5, 2017 22:50:02 GMT
hexpod I think you put wrong torque and gearbox efficiency, According to the specs it's 3.38nm rated at max 700rpm for that torque. www.teknic.com/model-info/CPM-MCVC-3441S-RLN/Also the efficiency should not be 96% for the gearbox, I would say 60% is more realistic. See attached sheet that I did the calculation for you, it's much closers to your empirical test results. 187kg... Thanks Thanos I do not think I made a mistake correction: the efficiency of the boxes in two stages in the catalogue is rated ≥94%! the teknic motor model is 3432S, not 3441S www.teknic.com/model-info/CPM-MCPV-3432S-RLN/ limited to 800rpm and 4.4 Nm
cheers
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Post by tronicgr on Jan 6, 2017 0:07:01 GMT
Well, the torque is not so much...
Cont. (RMS) Torque (@75 VDC) = 2.77 N-m (392.2 oz-in)
Don't count the region of peak torque, this is for short run accelerations, not full load.
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johann
Junior Member
Posts: 57
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Post by johann on Jan 6, 2017 11:16:37 GMT
Hi friends,
sorry I could not answer earlier. There are 2 questions to my reworked list.
1. Constant payload safety factor 1.5 this one is only used to calculate the colors of the platform load capacity. It has no influence to the values itself. You always get the result of Thanos basic calculation. For example payload 170Kg + safety factor 1.5 = 255kg. It is not used for any calculations only for the colors in the last 2 columns.
result 1 166Kg color red result 2 241Kg would be ok but color is yellow depending on safety factor 1.5 result 3 265kg is more than ok color green For this examples see my picture above.
2. Calculate gearbox efficiency inside the first line you have to give this value from datasheet for it and get as result the torque after gearbox and output RPM. Torque after gearbox is calculated as:
Torque after gearbox = (direct motor torque Lb-ft x gearbox ratio) x worm gear efficiency.
So far so good.
For line 2 I have from datasheet given the gearbox ratio, torque after gearbox and output RPM. So I used Thanos formula from line 1 and did the following calculation for the efficiency:
worm gear efficiency = torque after gearbox Lb-ft /( gearbox ratio x direct motor torque Lb-ft)
In both cases direct motor torque is calculated via motor HP and max RPM. If this is ok than the rest should be also ok. If not we have to change my formula in line 2
I hope this explanation is helpful and you get the answers you asked for.
Thanks Johann
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Post by hexpod on Jan 6, 2017 14:08:32 GMT
Well, the torque is not so much... Cont. (RMS) Torque (@75 VDC) = 2.77 N-m (392.2 oz-in) Don't count the region of peak torque, this is for short run accelerations, not full load. Ok, I got it. In this case the excel calculator is a bit pessimistic giving me 165 kg.
I see you decided to multiply a single motor capacity x2 to obtain a 6dof playload. That's gives a very substantial margin.
cheers
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Post by tronicgr on Jan 6, 2017 17:26:27 GMT
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Post by hexpod on Jan 7, 2017 9:47:33 GMT
vicpopo , do you have the information what is exactly the motor/gear combo used in the ckas v4 platform, or any other model??
it seems you did some investigation in that matter back then.
it would be interesting to compare with Thanos payload calculator if the australians used also "motor load capacity x2" to calculate the payload for their 6 dof products.
cheers
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johann
Junior Member
Posts: 57
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Post by johann on Jan 7, 2017 10:16:22 GMT
Hi Thanos, thanks for your new List. What about motors including the gear itself. This one which I've used inside of my reworked list? The datasheet gives the following information: power: 0.55KW output rpm: n2 = 18 gearbox ratio: i = 51 torque after gearbox: M2 = 182Nm worm gear efficiency: fs = 0.7 explanation see here www.js-technik.de/en/geared-motors-informationsThe only thing what is different to my calculation based on your first list is the value of worm gear efficiency. It’s calculated as 0.61 and inside the datasheet given with 0.7? See my list on page 2 and also the attached picture. You know I’m not the specialist to calculate torque based on some parameters from different kind of motors and datasheets too. What would you recommend to do? Thanks Johann
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Post by vicpopo on Jan 7, 2017 19:05:15 GMT
vicpopo , do you have the information what is exactly the motor/gear combo used in the ckas v4 platform, or any other model??
it seems you did some investigation in that matter back then.
it would be interesting to compare with Thanos payload calculator if the australians used also "motor load capacity x2" to calculate the payload for their 6 dof products.
cheers Hi Guy's , Ckas seems not using at all worm gears reducer because bad efficiency .Gear boxes are helical or helical bevel , the ratio is around 100:1 so between 8 and 15 rpm at the output gear box shaft. For the payload if you make the calculation with a better efficiency you need less power according the payload capacity. As I know ckas for its smaller 6dof has been used 0,25 kW ac motors and gear boxes helical bevel with 100:1 gear ratio ( 193Nm ) and for a payload between 150 / 180 kg. i don't know if this one is the V4 I used the same specs for my 6dof exept the gear boxes which are just helical , the output shaft is on the same axle as the motor shaft.
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Post by hexpod on Jan 7, 2017 21:18:04 GMT
"For the payload if you make the calculation with a better efficiency you need less power according the payload capacity."
Yes and no. For me it is not so obvious
I have also efficient boxes (around 95%) and without moving I am taking almost 50 perc. of my RMS.
I guess that with less efficient boxes (around 60%) I could draw much less without moving.
After that, I agree, to move this static load with less efficient boxes you would need more power but as you've just spared some on your static state, you automatically have more to use.
What do you think? does it make sense to you?
If somebody find the exact motor specs used in ckas platforms, please post it here
thanks
cheers
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Post by tronicgr on Jan 7, 2017 21:36:15 GMT
My opinion, we are talking for two different things in terms of loading the motor.
Here is a simple example
1. You have an AC motor with Worm gearbox. The gearbox cannot be back driven from the load so the motor only works when it needs to re-position the load. In that case it might have a little high current on start and lose much of the power due to low efficiency of the gearbox. But the platform will have stability, even when power is lost unplanned.
2. You have a bevel or bevel Helix gearbox on the same motors. It's more efficient for the motor and will not have much resistance to move even more load. BUT, the load can back drive the gearbox and the motor has to keep moving/apply torque on the gearbox to hold the position, ending up spending same energy as the worm gearbox solution. If the PID is not tuned correctly it will also have bouncing motion around the hold position trying to find target.
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Post by hexpod on Jan 8, 2017 1:52:36 GMT
My opinion, we are talking for two different things in terms of loading the motor. Here is a simple example 1. You have an AC motor with Worm gearbox. The gearbox cannot be back driven from the load so the motor only works when it needs to re-position the load. In that case it might have a little high current on start and lose much of the power due to low efficiency of the gearbox. But the platform will have stability, even when power is lost unplanned. 2. You have a bevel or bevel Helix gearbox on the same motors. It's more efficient for the motor and will not have much resistance to move even more load. BUT, the load can back drive the gearbox and the motor has to keep moving/apply torque on the gearbox to hold the position, ending up spending same energy as the worm gearbox solution. If the PID is not tuned correctly it will also have bouncing motion around the hold position trying to find target. Thanks for the precisions.
You are right, I've forgot that worm cannot be back driven at all. "ending up spending same energy as the worm gearbox solution" If I understand you correctly, at the end, worm and helical will apply similar load to the motor although their efficiency are significantly different. If that's the case, you could think to implement a efficiency coefficient for wormboxes in your payload calculator.
cheers
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Post by tronicgr on Jan 8, 2017 2:00:24 GMT
I don't think, it needs coefficient for the difference, either way you will have to spend energy to produce work. You cannot produce work from thin air. At least that's the case for constant loaded systems as the 6dof platform are. Perhaps that's why your motors gave less load estimate on the calculations a few posts ago... you can't really cheat physics laws...
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Post by vicpopo on Jan 8, 2017 8:56:19 GMT
My opinion, we are talking for two different things in terms of loading the motor. Here is a simple example 1. You have an AC motor with Worm gearbox. The gearbox cannot be back driven from the load so the motor only works when it needs to re-position the load. In that case it might have a little high current on start and lose much of the power due to low efficiency of the gearbox. But the platform will have stability, even when power is lost unplanned. 2. You have a bevel or bevel Helix gearbox on the same motors. It's more efficient for the motor and will not have much resistance to move even more load. BUT, the load can back drive the gearbox and the motor has to keep moving/apply torque on the gearbox to hold the position, ending up spending same energy as the worm gearbox solution. If the PID is not tuned correctly it will also have bouncing motion around the hold position trying to find target. Ok , but for a 6 dof playing with car simulation you don't have moments where the car drive without any acceleration .It's more true for a flight simulation ! All worm gears aren't not reversible it depends on the gear ratio and the gear components used ( helical angle). And for the load the big gear ratio is also a big advantage .Try to move the output shaft manually in the goal to move the input shaft.You will find a difference between a gear boxe with big ratio (100:1) than an another with low ratio (10:1) hexpod : for the efficiency what is always true is that P = C omega. So if you have less efficiency in the transmission you loose mecanical power needed to move the plateform.The result is that you have to oversize your plateform accoding the payload. I'm pretty agree with Thanos post for the energy cost ( should once measured according the payload between both technology (worm/helical).But it's not the same thing to compare. For the regulation for ac motors what could help is using an encoder in the motors to drive better the regulation.The most advantage is that the inverter could be drive the motor better on the moment where we want to sustain the load at 0 rpm. But it's more cost . One more point to mention in the quality of the gear boxes.If you choose a poor quality you will have some backlash which is a big problem for the regulation and a bigger problem also if the gear ratio isn't big. i would say don't spare money with the gear boxes , It's easier to find a suitable motor for our plateform than to find the right gear boxes
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