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shredder auto reverse for xx time under load.

mike strongman

shredder auto reverse for xx time under load.

16/03/2018 at 19:28

Hi guys,

I am working on a shredder design at the moment that is a little different than most others, its based on the small Filamaker shredder that Marek Patel has copyright free Cad designs for on his website :

Free Shredder Cad Files

I take no credit for the design just sharing it –

*** anyway – back to the question ****

I am looking for a way to auto reverse a motor if it gets jammed for a specific amount of time before going forward again. Is there a way of doing this ?

My setup – (plan only @ this stage) 5.5kw motor on a VFD geared at 23 rpm (It will have a 1667 Nm of torque roughly, as not only am I shredding plastic but also waste wood and tin cans etc) or a hydraulic 7.5kw motor with adjustable speed depending on flow rate.

The shredder is constructed out of 21mm steel and the blades are made from 21mm hard faced steel (or Hardox – not decided yet)

The danger is if it gets jammed …it can break the drive shaft.

I was thinking if the RPM drops below x amount it would reverse for 5 sec then go forward ? or like mentioned it jams and auto reverses

any thoughts or ideas anyone ?

many thanks


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16/03/2018 at 20:51

The member andyn did something like that:
at 3:20

16/03/2018 at 21:10

Yes I think thats where his design may have come from.. it looks very similar to the cad design I linked.. well the shredding knives and shredder body.

Would love to know how the anti jam works..

16/03/2018 at 23:11

Yes I did something similar, I put an encoder on the free end of the non-driven shaft, it’s just a disc with slots in it and an IR light beam, you can see it at 3.37 on the video. My machine is small and can withstand the force of a jam, so if it doesn’t receive a pulse from the encoder approx every second, it knows a jam has occurred and to reverse the motor, there is no sensing of the actual load or RPM, but with more accurate measurement of the pulse train I would be able to detect when a jam is about to occur before it actually happens.

Yes the filamaker shredder design looks very similar to mine, I didn’t base my machine on any particular design, but I may have seen this machine and other similar ones when I was looking for inspiration.

17/03/2018 at 13:08

Thanks for update.. will have a look andyn.

I am not sure if vfd’s can be programmed re parameters…

### update.. so I am looking into using arduino code.. Need to do research but appears the motor can be controlled in so many ways with this and with relative drivers / sensors

18/03/2018 at 23:50

Can a VFD be programmed to auto reverse if torque limit hit / overload ?

27/03/2018 at 19:56

andyn, very clever way to controll the load on the shredder. Please could You explain a bit more : what type of hardware are you using to controll it ?

Are You using some kind of logic controller like Simens Logo ?
Or do You know cheaper way ?
Best wishes .
and thanks in froward.

28/03/2018 at 15:09


Nothing complicated or expensive at all!

Just a £1 micro-controller (not even an arduino) and two relays to start/stop & reverse the motor.

I’m using a single phase motor so don’t need a VFD. VFDs can monitor the load and be programmed to shut down above a certain limit, I’m not aware of any with a reverse/clear function (there may be), but you could certainly use a micro-controller to control the VFD either directly via the start/direction inputs, or most have some sort of serial interface.

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