Dave m Posted February 28, 2019 Share Posted February 28, 2019 trying to help an art student who has the idea of spinning a series of mdf arms that have been cut out of 9mm mdf.She has maybe 10 arms, the overall width fingertip to fingertip is 3-4 feet. No idea of the actual weight. (I can find out)She had a very chunky mirrorball motor (obviously designed to be spinning something hanging off it) that she tried to use fixed to a vertical surface but the arms just stall.I think she needs a high torque low rpm motor. The mirror ball motor did 1 rpm that she said was too slow so maybe 3-5rpm?Any ideas for an affordable source for a motor? The student would be paying and is skint. Mains or Low voltage is ok. The ability to control speed while retaining torque would be good. Anything like a microwave turntable or record deck might be ok in normal use but not on it's side? Link to comment Share on other sites More sharing options...
Gerry Posted February 28, 2019 Share Posted February 28, 2019 A cheap battery operated electric drill/ screwdriver?CheersGerry Link to comment Share on other sites More sharing options...
beware Posted February 28, 2019 Share Posted February 28, 2019 Not an engineer, but my guess is you might need a large cog and a worm gear. Link to comment Share on other sites More sharing options...
Brian Posted February 28, 2019 Share Posted February 28, 2019 Take a trip to a scrap yard and get a windscreen wiper motor from an older car. Link to comment Share on other sites More sharing options...
bigclive Posted February 28, 2019 Share Posted February 28, 2019 You can get faster mirrorball motors. The lack of rotation was probably due to the mass as synchronous motors can't really start into a static load. They need a bit of give (the chain) to get up to speed. If a mirrorball motor was used it might work OK if the exhibit was turned on and the arms were gently pushed in the right direction. (They usually have no specific direction.) Are these arms just for decoration or are they actually doing something like lifting objects? Link to comment Share on other sites More sharing options...
Stuart91 Posted February 28, 2019 Share Posted February 28, 2019 Would any of these be of use? May well be overkill and out of budget for a student show. Link to comment Share on other sites More sharing options...
gyro_gearloose Posted February 28, 2019 Share Posted February 28, 2019 Try adding weights to the arm so that it balances at the point it attaches to the motor. This should solve the stalling issue as the arm will now require less torque to make it move, despite weighing more. Link to comment Share on other sites More sharing options...
Jivemaster Posted February 28, 2019 Share Posted February 28, 2019 All but the smallest mirror ball motors rely on a suspension chain to take up some of the starting torque as the motor switches on but the ball accelerates slowly. Link to comment Share on other sites More sharing options...
Brian Posted March 1, 2019 Share Posted March 1, 2019 As I read the question the arms in question are in the vertical plane like the arms of a clock. Link to comment Share on other sites More sharing options...
empyfree Posted March 1, 2019 Share Posted March 1, 2019 As I read the question the arms in question are in the vertical plane like the arms of a clock.That was my thought too, your shout of a windscreen wiper motor is a good one, possibly need some reduction gearing to slow it down. Link to comment Share on other sites More sharing options...
Jivemaster Posted March 1, 2019 Share Posted March 1, 2019 Four feet (OP's estimate) of anything made of MDF is not a student project if suspended, especially if also rotated, and possibly overhead. is there anything to be gained from the design of a ceiling fan? They are a direct coupled slow AC motor and a light weight fan designed to be suspended over head, and above people. Is there anything to be gained from the use of foam materials for the wings of model aircraft, either hot wire cut from block polystyrene, or sanded from polyurethane insulation foam. Maybe this would help divide the suspended rotating mass by 100, reducing the engineering of the suspension and reducing the injury in the worst case of failure. Link to comment Share on other sites More sharing options...
ninjadingle Posted March 1, 2019 Share Posted March 1, 2019 I saw a spinning house idea on George Clarke's Amazing Spaces - they used mobility scooter wheels and motors. Low voltage and easy speed control, should do the job? Link to comment Share on other sites More sharing options...
Stuart91 Posted March 1, 2019 Share Posted March 1, 2019 They toured the spinning house round the various Ideal Homes exhibitions. Looked quite spectacular, took a lot of time to set up. Apparently at one location one of the motors overheated and caught fire... Link to comment Share on other sites More sharing options...
bigclive Posted March 2, 2019 Share Posted March 2, 2019 They toured the spinning house round the various Ideal Homes exhibitions. Looked quite spectacular, took a lot of time to set up. Apparently at one location one of the motors overheated and caught fire... That's always a problem with any powerful motor. The idea of using a windscreen wiper motor sounds OK, but they do require a 12V supply that can put out at least 10A. And there's also the issue of "student wiring" and the complete lack of understanding that a motor will draw lots of current and then go up in flames if not protected properly. The joy of a simple mirrorball style motor is that if it's stalled it will try and reverse. And even if completely jammed solid it will usually just sit there and get warm without any major risk of smoke or flames. I have seen ceiling fan hubs mounted sideways as part of a store display and they didn't seem to be too bothered about running sideways. The slight issue there is that they do have a high mass, so even at a fairly low speed the wooden objects attached to one would punish stray knuckles and the heads of errant children without mercy. The original question is potentially a bit vague in that it would be useful to know if these arms are going to be carrying a random load or moving things. As soon as you add in variables like that it ends up being a powerful geared motor with a control box and suitable protection. Link to comment Share on other sites More sharing options...
Jivemaster Posted March 2, 2019 Share Posted March 2, 2019 Searching ebay gets lots of ceiling fans for £5 and more including a 12v camping fan for little money. There are also wall mounted fans. Once any mass is rotating it needs consideration for guarding. I'd want any MDF item to be mass reduced so much that harm was almost impossible, then I'd want it engineering so that failure was very unlikely. Has anyone mentioned balancing this rotating mass? An unbalanced fan will soon start to rip it's mount apart, unless it's mass really is trivial. Link to comment Share on other sites More sharing options...
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