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Thread: Trossen motor encoder not working properly

  1. Trossen motor encoder not working properly

    I've contacted Trossen support twice with no response.

    I purchased two of the following:


    Item : Robot DC Gearhead Motor & Wheel Starter Kit [InterbotiX Labs]
    SKU : KIT-MTR-WHL [KIT-MTR-WHL]


    I've been trying to get these motors to work properly off and on since they arrived. Both turn okay and I get a constant stream of pulses from Channel A, but both miss pulses in Channel B. I've tried a variety of signal conditioning methods but nothing fixes this.


    Is this a known problem and if so, how can I fix it?

  2. #2

    Re: Trossen motor encoder not working properly

    How are you testing whether you get the pulses?
    Do you have an oscilloscope you can post a picture from?

    Also, I've found Trossen to be good about responding, so my guess is they somehow is not seeing your contact attempts.
    Try some other method?

  3. #3
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    Re: Trossen motor encoder not working properly

    Generally we answer tech support through our ticket system, the e-mail address is on our contact page.

    How are you reading the pulses? Generally with encoders you need to attach them to interrupts as polling is not reliable at those speeds.

  4. Re: Trossen motor encoder not working properly

    Quote Originally Posted by Tyberius View Post
    Generally we answer tech support through our ticket system, the e-mail address is on our contact page.

    How are you reading the pulses? Generally with encoders you need to attach them to interrupts as polling is not reliable at those speeds.
    Now I have a support ticket.

    I first ran the motor using an Arduino and motor shield and looked at cha and chb using two external interrupts. I then tried various stock signal conditioning solutions. Finally I disconnected it from the Arduino, powered only the encoders and attached it to a scope to watch what happens with the encoder only while I turn it by hand. I got the same results each time. Channel A seems just fine, while Channel B seems to randomly, but consistently lose about 10% of the pulses. Feeling that I would soon be shaving a yak, I decided to post on this forum hoping someone else may have seen something similar.

    If lots of these have been sold and nobody is reporting a problem, then obviously I'm doing something wrong. If that is the case, I have a couple of friends who I can draft to help me look for something obvious that I've missed.

  5. #5

    Re: Trossen motor encoder not working properly

    Most hobby parts are made to hobby standards, not industrial enginering standards, so I'd totally expect there could be manufacturing defects.

  6. Re: Trossen motor encoder not working properly

    Quote Originally Posted by jwatte View Post
    Most hobby parts are made to hobby standards, not industrial enginering standards, so I'd totally expect there could be manufacturing defects.
    These motors are about $20 each and the kit with 2 motors and wheels is $71+ IIRC. Maybe my expectations are different? I would at least expect that there would be some mention of this in the product specifications. Like maybe that sensor readings may be +or- 10%.

    The reason I posted on this forum is the hope that someone else has used these motors and can say something like 'I've used them with no problems' or 'oh yeah I say that and it was xXX which was easy to fix by doing yyy'.

    I'm using these motors to study PID and Root Locus control theory and practical application which will require a consistent sensor output. If this is unreasonable with a $20 motor then I've paid tuition in my study, learned something important, and will move on.

    I sincerely hope you are wrong about these motors and aren't speaking for Trossen.
    Last edited by joepardue; 11-20-2016 at 10:41 AM.

  7. Re: Trossen motor encoder not working properly

    And just FYI among the signal conditioning efforts tested, I had the internal pullups set and I tried not setting them and using external pullups.

  8. #8

    Re: Trossen motor encoder not working properly

    some mention of this in the product specifications
    If it misses pulses, I think that's mentioned already: In the "warranty" section! I would expect it to detect each A/B transition. If it doesn't, something's loose, or mis-calibrated.
    I do not speak for Trossen, just out of experience of having used hobby parts for a number of years. Expect about 5% defective units from any hobby seller; higher if you buy from "straight from China" suppliers.

    I'm comparing to what I've seen of Industrial spec motors that are easily hundreds of dollars even for small power levels.
    Check out some industrial spec small motors: https://goo.gl/SG9MUy
    Some industrial spec small encoders: https://goo.gl/D0ErC0
    Some industrial spec small gearheads: https://goo.gl/RQwrPG

    When I say "I expect ..." I'm addressing the surprise I read in your post, not the veracity of your claim. I think from described symptoms that you may have a bum unit, and I would expect Trossen to honor the warranty on those. A motor with encoder, the encoder properly powered, should show crisp A/B square waves at 90 degree offset (+/- 10 degrees or so) when you manually turn the shaft. If that doesn't happen, it's likely that the encoder sensor is off-center or mis-calibrated in some other way.

    Anyway, when buying from reputable, US-based suppliers, like Trossen, Pololu, SparkFun, AdaFruit, and such, I'd expect to get good warranty service when things don't work out. Those suppliers typically buy a few of the units they sell ahead of time and test them out to make sure the generally work -- but there can still be manufacturing defects in their stock; I wouldn't expect them to test each and every unit that comes from the factory. This is also why they charge a mark-up compared to the cheapest thing you can find on other sales sites; warranty service costs money that has to come from somewhere!

    When buying from straight-from-China suppliers, they typically just forward whatever the claims from the factory is (maybe they translate them, using Google Translate or whatever ...) And the factory they choose is whoever claims to sell X for cheapest. And, sometimes, they ARE the factory, with a website tacked on. (The arch-example of this is Hobby King, which is one of the biggest such sites because they are slightly better than the average such site.)
    Last edited by jwatte; 11-20-2016 at 11:05 AM.

  9. Re: Trossen motor encoder not working properly

    Thanks for your thorough and reasonable reply.

    The Trossen return policy is for 15 days, and I'm well past that. They state that warranty is from the manufacturer and I'm guessing that means trying to get a Chinese company to respond, not a likely event.

    I have two friends who highly recommended Trossen so I intend to bully each into taking one of these motors and seeing if they think it is the encoder or me as that problem. I'll get back to this thread when I have their pronouncements since it is entirely possible that this is me and not the motors and I'd hate to leave an unnecessary stain on Trossen here if this is my fault.

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    Re: Trossen motor encoder not working properly

    Quote Originally Posted by joepardue View Post
    Thanks for your thorough and reasonable reply.

    The Trossen return policy is for 15 days, and I'm well past that. They state that warranty is from the manufacturer and I'm guessing that means trying to get a Chinese company to respond, not a likely event.

    I have two friends who highly recommended Trossen so I intend to bully each into taking one of these motors and seeing if they think it is the encoder or me as that problem. I'll get back to this thread when I have their pronouncements since it is entirely possible that this is me and not the motors and I'd hate to leave an unnecessary stain on Trossen here if this is my fault.
    I'll follow up on your ticket directly to address this officially, but if you have a defective product we'll gladly replace them free-of-charge. If for some reason you were still seeing issues with your replacements, regardless of reason we'd be more than happy to refund you despite it being beyond our return policy.

    Our return policy generally refers to 'I bought this and don't want it'. In cases where you might have defective merchandise we would definitely make sure you are taken care of.

    So with that said, I personally spec'd these motors with an overseas manufacturer. We actually do test these in-house using an Encoder/PID based motor controller rig to ensure they're within nominal ranges before putting them into inventory, for the exact reasons Jwatte explained (he's not a Trossen rep, just very helpful, FYI).

    The motors I have in my lab which I'm currently using to develop the DriveBotix (smart motor controller w/ encoder inputs built specifically for these motors, see attached for a sneak peek) aren't showing these issues, so it might just be a fluke or it might be that something slipped past our QA. Regardless, we'll look into it and ensure you're taken care of be it replacement or refund.

    Check your support ticket for updates!
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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