building a drum spinner

hi,
i am still in the process of building my first robot (trax) but am starteing to plan for my next robot, a drum spinner. i am going to order 20mm thick hdpe plastic off direct plastics for the walls which i will screw onto an aluminium base plate. to power the drum i will use speed 900s and argos drill motors for the wheels. Just a few questions:
-where is the best place to buy speed 900s?
-can i use the robochalenge 'battle switch' to control the drum, and does it feture reversing and does it work with dc?
-if not what should i use?
-i don't want to have a bar going all the way across te drum, what do other people do?
-i considered sandwiching angle grinder disks (4 or 5) imbetwween hdpe rod(90cm diameter), would this be effective?
- and finally could i use one of these batteries(link bellow) for the speed 900s and one for the drive motors? would i be better to buy new?
viewtopic.php?f=166&t=3989

No replies saying don't do this yet, finish your first then move from there, spinner are dangerous and you should build an axe bot etc.
Thanks
Max :lol:

-i considered sandwiching angle grinder disks (4 or 5) imbetwween hdpe rod(90cm diameter), would this be effective?

see topic: viewtopic.php?f=111&t=4035

Hey,
Just looked at price of speed 900s and found out how expensive they are! Are there better (cheaper) places to get them than Hobby lobby or are there cheaper alternatives eg. Car fan motors? Also, what kind of gear ratio do I need to spin the drum?

Car fan motor will be a bit cheaper but heavier.
Battle switch would have to be modified with a larger relay for either a fan motor or speed 900's, if you wanted a simple on/off.
As with other people on the forum I think it'd be better if you finish your first machine before starting another!

car fan motor will be alot cheaper if you buy one from a scrapyard

You could get away with a drill motor if you gear it right.

A drum is best made with a tube of steel 3 or 4 inches in diameter with teeth welded to the outside. Use Nylon instead of HDPE for the bulkheads. A battle switch will not be enough to switch the motor on and off. You will need to use something with a higher current handling capacity. I have used 40A car relays in the past but would recommend a 100A relay from jaycar electronics.

The battleswitch doesn't reverse and will work with dc current.

The best design which works with all the current drums is to run a solid shaft through the middle and have bearings set into the end of the drum.

Grinding discs would not work.

Those nicad packs should work fine.

Now for the important bit, FINISH YOUR FIRST BOT AND GET IT RUNNING WELL!!!! then look at other bots.

Quote:

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Originally Posted by typhoon_driver

You could get away with a drill motor if you gear it right.

A drum is best made with a tube of steel 3 or 4 inches in diameter with teeth welded to the outside. Use Nylon instead of HDPE for the bulkheads. A battle switch will not be enough to switch the motor on and off. You will need to use something with a higher current handling capacity. I have used 40A car relays in the past but would recommend a 100A relay from jaycar electronics.

The battleswitch doesn't reverse and will work with dc current.

The best design which works with all the current drums is to run a solid shaft through the middle and have bearings set into the end of the drum.

Grinding discs would not work.

Those nicad packs should work fine.

Now for the important bit, FINISH YOUR FIRST BOT AND GET IT RUNNING WELL!!!! then look at other bots.

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what kind of gearing would you need for a drill motor powered drum spinner?

A drill motor typically does around the 18 to 20k mark (with the gearbox removed of course) so you would need gearing of around 6:1 to bring it down to a point where the drill motor could quickly spin up the drum (it's always a balance between top speed and spin up time).

what sort of rpm could you get from that gear ratio?

around 3k