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Optical Encoders
Before our team goes to the CORI event on June 23, we are trying to improve our robot. One of our goals is to connect optical encoders to our shooter, and attach a camera to track the hoops. Our shooter uses two Banebot RS-775 motors with P60 16:1 gearboxes. Will the optical encoders given in the KOP work with these, or do we have to buy different encoders?
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How do you intend to mount the encoder, e.g. are using a live or dead axle, what is the axle diameter, direct drive or belt/chain/gear driven etc. How fast will you be driving the encoder. Do you plan to attach it to FPGA or Jag. Do you plan to use 1x, 2x, or 4x decoding. How do you intend to use the signal. PID, Take-back-half, Bang-Bang, something else? Some are more immune to noise than others. |
Re: Optical Encoders
The short answer is yes, they can be made to work.
For more details, consider the questions posed by Ether and let us know, so we can offer some suggestions. And, if you don't know what something means, say so, we'll be happy to explain. |
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I only know a few of the answers, so I sent an email to two of my programmers/electrical to try and answer the rest. What I know is: the shaft of the gear box is .5in, it is run belt/chain/gear driven etc., and at full speed (but we only go about 35%) it can go up to 3,408 rpm.
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I do not understand the question of dead or live axle. And the other questions I think my programmers should be able to answer.
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Dead axle => axle does not turn |
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1) Your 775 motor is connected to a gear box. 2) The output shaft of that gearbox is 1/2" diameter 3) There's a sprocket on the output shaft of the gearbox 4) There's a chain on that sprocket 5) That chain goes to a sprocket connected to the wheel 6) The wheel rides on a dead axle. How and where do you plan to physically mount the encoder? What is the gear ratio of the gearbox? What is the tooth count on the two sprockets? |
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All of that sounds right, but Im going to post a picture just to make sure.
I do not know how or where we will mount the encoder, what is the best way? The gear ratio of the gear box is a 16:1. http://banebots.com/pc/P60K-S7/P60K-44-0007 The tooth count I believe a 32 tooth on the big one, and a 10 tooth on the other. |
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Im having trouble uploading the picture..
If you go to our website www.stcharlesrobotics.com , I just put the picture as the first one. |
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I followed the steps, its not uploading them properly. But the ones one the website work.
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You are gearing the motor speed down with the gearbox, and then gearing it back up with the sprockets. Generally speaking, you want to avoid doing that if possible. I don't see a good place to mount the encoder without making changes/additions to the design. Perhaps you could drill a hole and tap threads into the end of each wheel axle and make an adaptor for the encoder disk. EDIT: See attached pic |
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When I try to upload the image it says:
Upload Errors aDSC_0142.jpg: Attachment in Progress. Can be deleted here. But I've sat here 5minuets and nothing has happened. |
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How large is the file you are trying to upload. |
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I have to agree with an earlier poster that there isn't a really good spot to mount the optical encoder. However, do you have a sensor that you could use to count the sprocket teeth or chain links as they go by? Hrm ... probably overthinking things...
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An RS775-12 free speed is 7300 rpm, and an RS775-18 free speed is 13,000 rpm. You numbers don't add up1. 1assuming the pronoun "it" in your post refers to the immediately preceding proper noun, i.e. the gearbox output shaft |
Re: Optical Encoders
The Banebot motor-18v (http://banebots.com/p/M7-RS775-18) has a 17040 rpm. After the P60 gearbox with a 16:1 deduction goes on (http://banebots.com/pc/P60K-S7/P60K-44-0007), it has a 1065 rpm. Then the 32 tooth chained to 10 tooth sprocket makes it 3408 rpm.
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I just found this. http://banebots.com/docs/EN-G0361-KT-Assembly.pdf . Is this the way to go?
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Factor in the loss of efficiency from the geardown/gearup transmission and it's less than that. |
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I would speculate that they do have the room to mount the encoders he linked to. It's mounted to X bar and should be able to slide back an inch or more.
Jengles, those encoders would be a good option. Although less costly options exist, those may require more work to get them installed. Another consideration: at 128 pulses per revolution, times about 1000 RPM, 128,000 pulses per minute is a lot of data. In software, there is a way to count only every "Nth" pulse (like every 8th pulse for example) that will allow your software to not have to spend all its time counting pulses. Have your programmers look into how that's done, as they'll need to learn how eventually.... |
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Hi,
I am looking into a similar option for my team involving encoders. We tried to implement some during build season but due to mechanical inaccuracies, we couldn't get them to fit on and read correctly. (We don't have a machine shop and use hand tools to make all our parts in house.) The banebots encoders that go on the gearbox would fit in nicely with our system, but I was wondering if they would provide an accurate enough reading for wheel speeds being attached to the gearbox rather than the axle. We have a similar setup with live axles, and chained banebots motors with attached gearboxes. We would use the encoders to vary the wheels speeds automatically. We already have a camera set up for alignment. I'm just wondering if the speed read at the gearbox can be used in the code with some adjustments for friction losses accurately. I don't do programming so I can't answer a lot of questions personally on how we wrote the code for the set up we tired to implement earlier. Thanks! -Anna |
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I had something similar happen, where I wasn't allowed to upload attachments. If you contact the CD staff they can assist. (I think it has something to do with rampant spam-botting.)
Anyway, here's what ours look like. |
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