DC motor selection?

Hi everyone,sorry i've not been really active lately ^^'

Today's question is in direct relation with my College project (Mechanical Engineering) so if you have something that might help me on the matter,I'd be thankfull.

Problem is: We need to drive 3 axis with DC motors.According to our calculations and goals we need at least a DC motor with a speed range (from minimum to maximum) of 20:1,preferably a geardown motor with speed around 500-4000 (we're gonna use a worm gear on a large gear to reduce it to aimed RPM).

So specifications; -DC motor running on 12 or 24Volts -Range of 20:1 (if higher range is possible,40:1 would be perfect) :D -Torque doesn't need to be outrageous since we fight against inertia -Light Weight

The project itself is based around 3 arduino working on a 200m distance (no more info for now,don't spoil the surprise^^) and i'm gonna post a complete review of it when done but since it's a college project,I can't do it before it's completed.

So your help in choosing the right DC motor would be greatly appreciated,any questions-­reply or pm. thanks^^ :D

any suggestion..someone? =(

You know what specs you need, you should be able to go to suppliers' catalogs and find something suitable. Although "lightweight" and "outrageous" torque are vague and relative--as an ME student you should be able to identify specific targets for weight and torque. And no offense, but isn't selecting and sourcing components a key part of this project?

Wow,that's rude. I've been looking for those DC motors for about 3 weeks now and no,it ain't the key part of the project since we are designing it from the base to the top,milling turning and trimming all the tiny aluminium pieces,those motors are just an obstacle yet to overcome.

The fact that I didn't supplied specific torque is pretty simple,we are going to design the hellical gears to bring torque and RPM in the range we want.

That said,the problem I faced looking for those motors is the min speed max speed ratio; I need at least 20:1 and 40:1 would be perfect but still,my searches didn't gave me a clue.

so I tought after 3 weeks of wasted time I'd ask clever peopl who might have faced the same problem and provide me with enlightment.

Thanks.

Perhaps if you checked out some mechanical engineering forums or such, they might be able to help. The forming of specifications and then selection of your motor for your application is a mechanical engineering task at it's basis, and might be slim pickings from this forum members skill sets.

Lefty

Yeah kinda,but since the whole system is based on an arduino network,I tought I'd have some great answers from this forum^^

I did not mean to be rude, but your OP didn't identify any particular problem with sourcing parts that meet your criteria, and I've not heard of an engineering project where spec'ing and sourcing components was not a part of the assignment. After all it's no good designing a system that you can't find parts to build. You must have some sort of torque value in mind, after all you don't gain torque via gearing without losing speed or vice versa.

If you've been looking for three weeks, well, where have you been looking? What's your budget for price and power?

We are in the process of designing actually,which mean we could fit a large variety of motors,varying kuch of the other elements according to the DC motors,I was just looking for an advice on DC speed control to choose a correct one. thanks anyway

It is hard for us to come up with a resonable solution to your problem becuase it is hard to tell what your problem is exactly. Are you looking for little hobby motors with 1oz-in of troque or larger motors with 1000 + oz in. It makes a big difference. You say the big problem is the min-max speed range.

What is the final speed range? What final output torque are you looking for?

This site sells a bunch of small motors with gearboxes. http://www.pololu.com/search/compare/51

By speed range I mean from minimum speed to maximum speed like 20:1 meaning 1rpm is the min and 20 the max,or a 1000 rpm as the min and 20 000 as the max.

We want to achieve a specific turning speed for precise control and for speed movement so the range is the critical spec of it.

For torque let's say we want to beat the inertia of a 40 pounds balanced rig. The fact is,if we get a motor with medium torque and some high rpms,we'r gonna decrease it to fit the system,yet so far,most motors i found were about 12:1 range ratio from max to min.

The torque needed is something we can't calculate right now since we don't know the final gearing until we have a speed range from the motor specs so my guess would be,maximum torque we can achieve on a geared down DC motor with a size around 2X2X8 inches and weight around 1 pound or so.

also,i think i mis-explained my self…

when I said 20:1 I actually meant (Maximum rpm/Minimum Rpm),not gearbox ratio.

like this:
1000rpm at 6v
20 000rpm at 24v

The torque needed is something we can't calculate right now

Why on earth not? You know the mass of the load to be moved and presumably have some target for acceleration, F=MA, factor in the mechanical advantage of your end mechanism, add in mechanical/aerodynamic (if significant) drag, and bob's your uncle, you've got a power figure for your motor+gearing.

Well,I do know the mass but for the reference:

F=MA apply to linear movement,not rotation (i had like 4 advanced physics course ?thankyou)

We just don’t care about the torque as soon as it’s average since we are fighting against inertia,whatever,if you can’t jsut suggest me suppliers of DC motors,stop trying to act like your so clever(you kinda pissed me off on this one,sorry for that… :-/ ).