[chbot] electonics & motor current question.

[Charles Manning]

17A sounds excessive for any small battery, the switches etc so if you're 
seeing 17A then I suspect it is operating outside of spec. If indeed the 
system should be drawing 17A then I'd have a good look at the components and 
determine if they're likely to provide a reasonable lifetime when switching 
and supplying 17A.

As Mikael says, there should likely be some mechanism that prevents it from  
stopping it on live area and only stopping once it gets to the dead spot - ie 
sometime along the lines of what a windscreen motor does. Perhaps this 
mechanism is disconnected or has failed.


On Sunday 07 March 2010 10:22:52 Mikael Stewart wrote:
> The stall torque of a brushed DC motor will vary with commutation angle and
> depend on the number of armature poles. It sounds like the gun was designed
> for the motor to build up some speed and momentum before engaging, so it
> should have some mechanism to stop rotating after the last shot. Otherwise
> it should have been designed so that the minimum torque seen at stall be
> enough to charge the next shot.
>
> How old is the gun?
>
> Regards,
> Mikael
>
>
>
> ----- Original Message -----
> From: "Carl Ranson" <carl.ranson at gmail.com>
> To: "chbot" <chchrobotics at lists.linuxnut.co.nz>
> Sent: Friday, March 05, 2010 9:36 PM
> Subject: [chbot] electonics & motor current question.
>
> > Ok, so i've been asked to diagnose a fault with an airsoft gun.
> >
> > basically a motor drives a gear-train to pull back a piston against a
> > big spring. the final gear has half of its circumfrunce covered with
> > teeth, so that it drives the piston for half it's cycle and then quickly
> > lets go of it.
> >
> > the problem seems to be if you hold down the trigger too long, it
> > re-engages the piston.
> > So starting with the piston engagd it seems that the motor/battery isn't
> > strong enough. it draws upwards of 17A.
> >
> > my question is this...
> >
> > given a motor/gearbox that usually draws <3A at 9V , is it possible that
> > the same arangement, starting from a stall where the piston is engaged,
> > wouldn't work at 16A.
> >
> > my hope is that i can demonstrate the battery supplied is insuffiet so
> > they don't have to return the whole  system under the consumer
> > guarentees act.
> >
> > Cheers
> > Carl .
> >
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