66 replies to this topic

[skipjack]

i finished a batch of round stars this weekend, using my new starrollingmachine.
it's got a few modifications compared to the classic starroller, which is why i'd like to introduce the concept to the board ...


from left to the right:
Back / Front / Front with bucket inserted / 10mm Stars

the construction is based on an old washingmachine.
as their electronic parts usually wear off first, chances are high that you find an old washingmachine where the motor is still working.

i detached all the unnecessary parts, filled the washing-drum with rubberfoam and pushed a bucket (white on the picture) inside. the rubberfoam keeps the bucket in the washingdrum, not allowing it to tumble or move.

now you can put another bucket (green) into the "base-bucket" (white) and also remove it in the same easy way.

this handy feature has a few advantages compared to the classic starroller:

1) fast and easy clearance of the rolling-drum when sieving out the stars, that reached the desired diameter.
2) easy to clean
3) possibility to use more than just one rolling-drum (every starcomposition its own)


happy construction!
Skipjack

[Arthur Brown]

You use a DC/universal motor with brushes and sparking commutator for driving pyro compounds!?!
Please look for inspiration with either an induction motor or a remote drive.

[adamw]

The mechanism is novel but yes, don't use such a motor!!! Especially the way the back of the motor (with the brushes) is facing the bucket!

[Arthur Brown]

If that's your idea of a safe machine then you wuold be lucky to get Sectioned under the Act before you get live cremated. Bare belt and pulleys unsheathed wiring......... You shouldnt rely on someone else wanting to remove your partially burned body. If you are to play with flamable solids not with a dodgy machine please.

[burningbush]

good idea on replaceable bucket!
bad idea on no shielding of motor and pulleys!

P.

[skipjack]

thanks for your input guys. i'm always open for suggestions that can raise the safetylevel. shielding the brushes is definately a good idea.

@ Arthur: i very well got your point already after your first post.
but anyway ... thanks for illustrating your concerns a second time in a more dramatic way.

Edited by skipjack, 10 May 2005 - 09:07 AM.

[Andrew]

Good machine, looks a bit funny, makes some really nice stars.

Come on guys, I know that Americans have a little less computation power between their ears, , and that they like commiting suiside, but how about a little constructive criticism. He has worked really hard to rip and washing machine apart, and then rotate the drum and then angle it up a bit.

On the motor point, yeah I know, here we go again!, because the machine is so big it's pretty difficult to get comp near the motor or belt. In fact under normal conditions I'd say it's pretty close to impossible. The only way comp could get near those parts is if you tripped and threw a box of it over the top. And as you would have it turned off when loading etc. , it would not be too much of a problem. Wet comp isn't going to fly out up and back, so under normal circumstances that isn't a problem either. However, you do need to cover all angles, accidents always happen because of laziness, something really simple, or something that insanely improbable that no one on earth would ever have seen it coming.

Not turning it off and having comp lying around when loading etc (Laziness).
Say the comp got a little dry, when you've dust, so on and so on, maybe boom (Simple).
Motor gets too hot, burns out and sends nasty hot stuff everywhere, not too good (Simple).
Perhaps a bit could break off and take a 'Buz Lightyear' tour of the garden and then end up going straight into the bucket and then it could cause you wet comp to ignite because of friction and then, and then, and then (So insanely improbable that no one on earth would ever have seen it coming).
I'm sure I've said enough on that.

A few Hints;
A secure lid on the bucket would be a great idea.
An enclosed motor/pulley action is also good.
Perhaps a few thermal fuses in appropriate places.

These three relitively small things would rule out pretty much all the real risks.

Hope this helps

[alany]

Where does it say it is a universal motor anyway?

The washers/dryers I've seen use induction motors for long life.

[sasman]

In the next few weeks i am going to try to build a star roller..I have got the Star roller video from AFN with harry gillian and tom perigrin.. and i like the look of the machine .. it looks very simple to make..

It looks very similiar to this one from TNL http://www.t-n-l.com/roller.html .
It's a very simple design , a DC motor powers an off centre cam which rotates against what apears to be a thick piece of circular plywood. this acts as a large pulley/gear .The Stainless steel bowl/drum is fastened to the plywood . on the video you can see that to stop the drum bouncing of the cam it is pulled back with a large rubber band?..this also keeps tension on cam/pulley .This cam gives a wobble to the drum so agitates the stars whilst rolling

The electric motor has a variable speed control and the motor is sealed inside some square section steel tubing..all joints are welded so should be explosoin proof?..

I have just looked on ebay for some DC electric motors but not sure how big a motor would i need?..any ideas? on HP wattage? amperage?..

I am not going to make massive amounts of stars..Most likley i will settle for a 32 cm diameter stainless steel drum ..the amount of stars will be no bigger than 2 or 3 kg

Cheers

Edited by sasman, 13 May 2005 - 04:53 PM.

[Yugen-biki]

I use a (certified for use in explosion hazard environments) 250W motor with a speed contoller. I have never used all the power.
My bowl (stainless steel) is about 20cm at the top and 15cm at the bottom. That is enough to make about 1,5Kg stars at a time.

About welding, as long as it is gas proof it is safe. But the motor needs ventilation/cooling!

[sasman]

I have got myself a 30 cm Stainless steel stockpot should be more than ample for my star rolling needs...and have just manged to get a 400watt 24 v dc motor of of ebay Nelco sealed unit i went for this motor because it says it is sealed..All i need now is a Dc motor control...
i have looked on ebay and the one's that are big enough for this 400w motor are more expensive than the motor i have just bought?.

Has any member got any good CHEAP!! way of controling a DC motor?..

[burningbush]

You can try a dimmer rated to the amps it pulls, "for lights"
I dont know what kind of motor it is? Shaded pole, how many leads does it have? 2. I assume. Off hand I cant think of a control circuit thats CHEAP for 17 amps,
maby a ajustable gear box might be a way to couple it and have differnt speeds.

hope that helps.
Pc

[alany]

Chunky MOSFET + 555 in a pulse width variable mode would be my suggestion. Typical topology uses two diodes to ensure the charge and discharge paths go through opposite branches of the same pot, so the frequency is constant, but the wiper angle determines the transition point. The sweep is fairly wide and linear, sufficient IMO for speed control at least.

More complex PWM generators use two 555s or a 556, one to generate the timebase and the other as a monostable to control the pulse width. A single 555 generating a sawtooth timebase with an op-amp comparitor to control the pulse width is also popular. Something similar and superiour can be made with a dual op-amp alone, like a LM1458 but all three circuits are probably more complex than required. The only advantage of sawtooth/comparitor circuits is precision and range of sweep, especially when a constant current source is used to generate a linear sawtooth.

As you need to switch rather large DC currents into an inductive load a MOSFET is probably best, and care should be taken driving its gate. The motor must have a snubber diode across it, and a small capacitor to supress RF hash is also advised. A large power bipolar could be used, but you'd want to buffer the PWM output with a low impedance drive into its base or use a darlington. A low impedance drive to the MOSFET gate isn't a bad idea either to get nice sharp edges. 25 kHz or so should be a good base frequency for the PWM oscillator.

[Arthur Brown]

That motor will likely NOT run at the sort of speed you want for star rolling. Look at running it at full speed and using a belt drive, even using stepped pulleys (cf. pillar drill ) to allow speeds in the order of 20 - 200 rpm depending on your barrel dia.

Likely the field winding needs RATED volts applied and armature needs a variable DC applied DC motors prefer variable DC with smoothing rather than pwm or phase angle chopped AC. When running slowly the torque will be reduced and the motor may overheat, sometimes additional cooling is required.

Remember 800rpm is a spin dryer!!!!!! you will need much less than that for the stars to roll

When you find where the motor was made then you can ask the manufacturers for assistance controlling it

Edited by Arthur Brown, 31 May 2005 - 10:29 PM.

[sasman]

The motor is rated at 1600 rpm...to drive the drum there will be about a ratio of between 10 to 1 or may be 7 to 1 this will then drop down the drum revs to about 160 rpm.....I am hoping to vary the voltage to fine tune the rpm of the motor..or if need be use an electronic control method...

When i have tried to connect the motor i have found 4 wires instead of the normal negative and positive?..the motor has seperate field and armature excitment?..

i have no idea on how to wire up the damn thing?..4 wires yet i only have + and - wires?...