New encoder boards - Need to update the name and docs...
RobotWorkshop
Posts: 2,307
It is great to see that the new quadrature encoder boards for the wheel kit are available from Parallax:
http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/29321/List/0/SortField/4/ProductID/869/Default.aspx
This makes the wheel kit more attractive for other robot controllers which expect quadrature inputs. I think that it is unfortunate the way the new product is named and will end up causing confusion with the original version here:
http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/665/Default.aspx?txtSearch=position+controller
Reading the product pages it would seem to the casual observer that both of these will report 36 positions back to the controller. Just looking at the encoder wheels I can see that is wrong. The original encoder wheel has 9 dark and 9 open segments which can give 36 different positions. The new encoder looks like it probably has 4 times the resolution. However it looks like it is being advertised as a lower resolution encoder and that the only difference is that it has a raw quadrature output.
Can someone from Parallax (Matt??) comment on these and confirm what these new encoders really put out?
Robert
http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/29321/List/0/SortField/4/ProductID/869/Default.aspx
This makes the wheel kit more attractive for other robot controllers which expect quadrature inputs. I think that it is unfortunate the way the new product is named and will end up causing confusion with the original version here:
http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/665/Default.aspx?txtSearch=position+controller
Reading the product pages it would seem to the casual observer that both of these will report 36 positions back to the controller. Just looking at the encoder wheels I can see that is wrong. The original encoder wheel has 9 dark and 9 open segments which can give 36 different positions. The new encoder looks like it probably has 4 times the resolution. However it looks like it is being advertised as a lower resolution encoder and that the only difference is that it has a raw quadrature output.
Can someone from Parallax (Matt??) comment on these and confirm what these new encoders really put out?
Robert
Comments
You are dead-on accurate - the Product description definitely needs to change, my bad.
Bottom line first (then the explanation):
Old encoder = maximum of 36 positions per wheel revolution.
New encoder = maximum of 144 positions per wheel revolution.
Backup data:
The old encoder "insulated" the user from the raw data (as you know). This new Encoder simply delivers two steams of pulses, whereas the "old" encoder had a built-in pre-programmed microcontroller that insulated the user from the raw data.
The old one had a 9 position disk, which resulted in the ability to resolve to 36 discrete positions. (rising and falling edges of two channels = 2 x 2 times the number of positions on the disk = 2 x 2 x 9 = 36 discrete "ticks".
The *new* encoder has a 36 position disk. Couple that with a quadrature data stream, and you get 2x2 (rising and falling edges of two different channels) x36 raw encoder positions = 144 discrete ticks of resolution.
We're just wrapping up (today, in fact) the new revision of the MMWK (#27971) which includes all this data. I shall port that over to the web description pronto!
You guys/gals keep me hoppin' here :-)
Thanks!
-MattG
I think these new encoders will enable the wheel kit to be used for many other projects now that these new encoders are available. I need to get a pair of these new sensors to try out. In particular these may work out well with the LEAF controller board and LEAF robot project. They will be on my Christmas wish list...
It would be good to keep the original "intelligent" position controllers around since many people have already built those into projects and they are useful to offload the motor control functions form the host and also let those motors work with controllers that may not have the resources to control the motors directly.
Robert