Mechanical Design Assistance???

Same here RWReynolds, but try this calculator for gear reduction to decrease speed Mechanical Gear Reduction Calculator

C

Edit: How about placing LED's around and turning on/off the set you want? Just thinking outside the box.

Thanks for the info Clem...

Yeah, that's kind of why I'm looking at stepper motors. They are pretty efficient and some of them have resolutions of less than a degree. I could control the rotation speed completely and dynamically. I'm just not sure which one will handle the load. And placing LED bars around the cultivator unit would be cost prohibitive. A motor is about $30. The LED bar is $150.

I did, however, decide on a planting container this evening. These are pretty cool and now I can estimate the total weight more accurately. Check it out.

Cheers,

Rick

Hi Rick, From your description and design it looks like all you will have to over come is the inertia of your cultivator and what ever friction there is in the lazy susan bearings. Since you are talking about a very low RPM (Only about 2 times as fast as the hour hand on a clock) and you do not have to have high accelerations in the lazy susan you will not need that great a torque. You can test your needs by measuring the radius of your drive gear and test to see how much force is required to turn the lazy susan at that radius. A stepper will not produce a continuous motion at these low RPMs and the frequency of your steps may be determined by the minimum step angle of the motor. Your gear ratio motor to lazy susan will also have to be taken into account. I am guessing that you will be gearing down to produce the low RPM and this will make it easier to use a low torque motor as the gear ratio will amplify the torque of the motor. I hope this helps and good luck.

John

Try one of these.

http://yourduino.com/sunshop2/index.php?l=product_detail&p=126

You don't need to worry about the torque as they are geared, and almost unstoppable.

John is quite right about using a stepper snce they are the best option for this slow speed.

Mark

Thanks John,

I thought the stepper was a good idea because of the level of control and the efficiency. If I have a geared stepper that has a step angle of less than one degree, I see a lot of these, shouldn't I be able to step it as slowly as I want. It's just a pulse per step right? My point is, should I really need anything other than a 1:1 gear ratio for my drive gears?

I know that when the motor is not powered it is free wheeling. But I'm moving so slowly and should have enough weight and friction here that it seems like I should be able to apply power, set direction, pulse a few times, let it settle and shut it down. And not have to worry about unwanted movement when the motor is powered down. Does that make sense?

Anyway, I think I will acquire one of the small inexpensive steppers and do some experimentation. If the one Mark linked to would work then I can afford to play. If I need something in the $30 - $40 range then I need to know exactly what my requirements are before purchasing.

Cheers,

Rick

Thanks Mark,

Are you thinking the one you linked to would do the job? $5.00 to do the job would be pretty nice indeed!

Cheers,

Rick

Hi Rick,

I believe that a 1:1 ratio will probably work. If your stepper steps at 6 degree increments you would take 1 step every 6 minutes in order to have 4 revolutions per day. You can measure the torque needed to turn your lazy susan by attaching a spring or a rubber band to the lazy susan and noting the distance to the center. Pull the spring / rubberband until the lazy susan moves and note the length of the stretched spring. Now hold the spring vertical and add known weights to it until it is the same length as what you observed moving the lazy susan. Your weight times the observed distance to the center of the lazy susan is the torque needed to move the lazy susan. If your stepper has at least this much torque it should be capable of making the lazy susan move. If it is short of the needed amount it will just bump without moving as the magnetic fields slip past each other. It might also be good to plan some elasticity in your motor to susan drive link so that the motor doesn't experience too high of an impulse from the time required to accelerate the mass of the lazy susan.

John

Rick  RWReynolds

I can assure you it will turn your turntable easily. 

Being geared it doesn't freewheel, and if you check the specs its 64 :1.

Terry has example code which shows it needs 2048 pulses for one shaft revolution.

You have lots of options ...

I'm off in a few hours so I'll be unable to respond but John should be able to assist with the mechanics/

jw0752

Mark

Thanks again JW!

That really helps on the cost and gives me all the control I need.

Cheers,

Rick

Thanks again John,

That;s exactly what I needed. A great step by step experiment. Looks like fun.

Yeah, I had in my head to maybe place a small spring laoded tensioner pully or gear somehere in the chain.

Cheers,

Rick