Need help finding the right motor

[228signguy]

Hello All,
I'm putting together a proposal for a set of face lit (led) channel letters, mounted to a raceway. The customer has a cycling fitness business, and two of the "O's" in the name are also wheels. Her website has these wheels spinning and now I am looking into adding this feature into her sign. The permitting office said that they're ok with it rotating, but it can only rotate at like 1 rpm. I have never done anything moving before, and almost everyone that I've reached out to said that they could not help me with determining what I would need.
It is a white circle w/ black spokes and a black outline w/ a stationary 'fleur de lis' symbol in the center. The black spokes rotate clockwise on the white background.
I'm thinking about basically making a channel letter that has two faces - the internal face will be attached to a rotating device and will be the only moving component. It will most likely be 1/8" or 3/16" white plastic w/ black vinyl applied to the surface for the 'spokes' on the wheel and it will have a diameter @ App. 29.25". The can will be app. 30" (or slightly larger than the white plastic face) and will have a clear plastic face w/ 1" (or 2") Jewelite. On the clear face I will apply the vinyl decal of the Fleur de Lis, which will remain stationary and cover how the white plastic face attaches to the shaft, or whatever it will be. I'm thinking that the clear face will also protect the rotating face from wind load that may cause stress on whatever motor or device I use. It doesn't seem like the white rotating faces would weigh more than a few lbs. Does anyone have any tricks up their sleeves when it comes to doing this, or know of a company that could give technical advice? I found one company, but the cost of the motors was more than the cost of the entire sign. One tip that I heard from an older sign guy was using a motor from a ice cream maker. I don't know about that, but I did think about the motor used for the Waiver Mannequins. They seem to do ok outdoors, but I don't know about continuous use. I would set it up inside the raceway, and maybe have to make a box around it to further protect if from the weather.
I have attached a file to help illustrate what I'm trying to do.
Any help or suggestions will be greatly appreciated. I do apologize for how long this is, but wanted to try to be thorough.
Thank you for your time,
228SignGuy

 

[Skogsgurra]

Google "fhp geared motors" to get tons of ideas. FHP stands for "Fractional Horse-Power" because you will not need much power for this.

For least complexity, I would use a standard AC single phase motor and IP 54 or better. IP 54 doesn't really work well outside in rain and snow, but it is cheap and you seem to plan some kind of protective housing for it anyroads.

How much power you need? At that speed, you could do with 10 W, but that is ridiculous. Go anywhere between 25 and 100 W. There's usually a sweet spot where volumes are up and costs are low. Use that criterion instead of torque calculation.

For variable speed, use a three-phase FHP motor and a small VFD. Avoid DC motors, mostly because the brushes need regular service and replacement. And that, they will probably not get when it is needed. An "animated" sign that is stuck is not a good idea.

I see a possibility to use one motor and a mechanical link between the two "O":s. That *could* save a few dollars in motor cost, but the extra hardware (sprockets, chains etcetera) will eat those dollars many times over. Reliability will also go down the drain.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

For a sign, likely exposed to the elements and difficult to access for maintenance, I would look into simulating rotation, maybe with LEDs in a chasing pattern. The 1 RPM restriction likely is the result of an ordinance to try to protect wildlife (my niece writes specs like that for a living). Having no moving parts means being about to keep it closed to avoid providing a nesting place.

Just my two cents...


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[itsmoked]

I would agree with Jraef that, if at all possible, modernize the sign and the look with a LED based display where the LEDs are lit in patterns that provide the look you need. Think Las Vegas. Big bucks didn't reach for archaic mechanical motion, they went for more serviceable lights.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

I think that the retro look has its merits.
If you make only the wheels electronic - and jerky at that - and keep the rest, I think that the sign won't stand out at all. It will be just another one of those signs.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

As a certified slide-ruler-porter you make a point.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[228signguy]

Thank you guys so much for the feedback. I was playing with the idea of using lights to create the effect but put that idea on the shelf because I wasn't sure if it would give the same effect the customer is expecting and wasn't sure if it would be visible enough during the day. I would be housing the motor in either the raceway that all the letters are mounted to (which houses all electrical connections and gives accessibility for maintenance) or inside the letter (wheel) itself, which I would remove the face of the wheel for accessibility. I am currently doing some research on the suggestion from Skogsgurra, but its all over my head at the moment. I found some motors from a company but it seems like what they are trying to offer is overkill for what I need. An old sign man suggested using the motor from an ice cream maker, but that doesn't seem like it's meant for longevity - maybe to get the job, then not worry about the problems that may come 1 year later, or less. I played around with the idea of using the motors that are used in the street side "Sign Waiver Mannequins" as they seem to be made to resist weather and for continued use during the day. But I am apprehensive of using them without getting some professional advise, plus I haven't been able to find where to get them. I very much appreciate the responses and feedback from everyone.

 

[jraef]

This is kind of what I had in mind.

But if you are hell bent on a motor, there is a LOT to consider.
Duty cycle.
Expected lifespan.
Ambient temperature range.
Orientation.
Bearing design.
Mass that needs to be accelerated.
Time to accelerate (even though that may not happen often, you don't want to overload the motor when it does).
Effects of wind on the sign.
Effects of icing (if any, for all we know you are in the tropics).
Direct drive, belt drive or gear drive?
Cost to a stop or braking? If cost, what keeps it from spinning on it's own?
Does the moving portion need lighting? If so, you will need slip rings. If not, when is it going to be off at night? (affects restarting issue).

There's more to this, I'm just pointing out that it's not a simplistic as just "go buy a motor".



"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Skogsgurra]

That's not helpful, Jeff. It's more like showing off. Not at all you.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[tygerdawg]

I'm feeling generous tonight. And I feel like using metric units.
Did a quick check of specs on the web, and...

(It's Whisky Wednesday...somebody check my arithmetic)

You must calculate your required torque, T = Ja
J = mass moment of inertia for a disk
a = "alpha" = angular acceleration ~ (DeltaSpeed)/(DeltaTime)
J = 1/2 Mr^2
m = (area X 1.07 lb/sf) = 2.3 kg
r = (29.5"/2) = 375 mm = 0.375 m
J = (1/2)(2.3 kg)(0.375 m)^2 = (1/2)(2.3 kg)(0.14 m^2) = 0.16 kg-m^2
a = deltaThetaDot / deltaTime =
deltaThetaDot = (final rotation speed) - (start rotation speed)
= (1 rev/sec) - (0 rev/sec)
= (1 rev/sec)(2*PI rad/rev) = 2*PI rad/sec
deltaTime = 1 sec - 0 sec = 1 sec
a = (2*PI rad/sec) / (1 sec) = 2*PI rad/sec^2
Torque required = (0.16 kg-m^2)*(2*PI rad/sec^2) = 1.01 kg-m^2/s^2 = 1 N-m (hardly anything)

If you follow Skog's excellent advice you'll find millions of closed frame 120 Vac 1RPM gearmotors (this example is for a hotdog roller application) with 90 lb-in of torque

https://www.multiproducts.com/sites/default/files/sites/default/files/9000ac_1rpm.pdf

With some research you could probably find something cheaper & more appropriate. And probably the hubs you'll need, also.



TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[Skogsgurra]

No way that I check that math.

But the OP said 1 rpm, not 1 rps. So torque is on sixtieth of "hardly anything"

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Skogsgurra]

Or is it "hardly anything"/3600?

Not much - that's for sure.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[tygerdawg]

Seconds...Minutes...Who's counting?
Oooops...I see my glass needs a refill.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com