Determining specs for unmarked electric motors

[Bretina]

Hello,

This is my first post here and I registered as per my specialty which is marine biology but it seems I'm the only such member. I do however, have an electrical question if it's allowed to cross forums.

We're planning to develop and ocean going autonomous data and specimen collecting submersible robot. I'm in charge of component procurement and I hope to mitigate the high R&D costs by scavenging used components to try out prototypes first.

I've located a source for used electric motors but they are all unmarked except for the occasional voltage stamp. How can the other specs, such as amps, torque, rpm or even voltage be determined on these unmarked electric motors? Is there a machine to connect them to which tells the specs or are there shops that specialize in this? Also, I have a multimeter and a benchtop power source if this is typically done with these tools. If so, how?

Thank you.

Bretina
FL, USA

 

[Skogsgurra]

I doubt if you can gain anything from such an exercise. A much better way is to determine what you need. And then buy it. I guess you are talking about DC motors? Or is it AC? They have very different specs and the procedure to "back engineer" a DC motor is totally different from an AC motor, single phase or three phase.

You may guess motor voltage from the equipmet you are scavenging from. The battery voltage is usually, but not always, the peak allowed motor voltage.

If you are worried about research costs, there must be a lot of better ways to reduce them then to use unspecified motors with unknown remaining hours and problematic spare parts supply.


Gunnar Englund

http://www.gke.org

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

 

[jraef]

If you are worried about research costs, there must be a lot of better ways to reduce them then to use unspecified motors with unknown remaining hours and problematic spare parts supply.

And the inevitable fire or damage that makes your robot inoperable caused by not getting everything exactly correct...

The reason you can acquire those so inexpensively is precisely BECAUSE whomever has them now recognizes that the risks and costs to investigate them are higher than any potential replacement cost. Time to move on to Plan B... As Gunnar says, start with what you NEED by having a mechanical engineer determine minimum torque and speed requirements, then have an EE match those to you electrical system capabilities, then look for bargains that match those criteria. They are out there.

By the way, the reason you do not find any other Marine Biologists in an Engineering forum is likely because, at least when I was in school, biology tracks were not considered "Engineering"!

"Will work for (the memory of) salami"

 

[Bretina]

Thanks for the reply.

Yes, it will be battery powered and likely DC 12v. The source for the used motors says they test them to be sure they work and if they can be easily opened, they will to check for unusual signs of wear. The savings are 80-90% and available locally.

I'm stunned this isn't a relatively easy thing to do since electric motors have been around for over 100 years already.

Bretina
FL, USA

 

[jraef]

I'm stunned this isn't a relatively easy thing to do since electric motors have been around for over 100 years already.

Yes, but BECAUSE it is not easy to do after the fact, 99.99% of motor manufacturers permanently affix engraved or stamped metal plates on the motor stating exactly what it is and what characteristics it has. The ones that do not are those that do not want the users to be able to replace them with off-the-shelf motors, forcing them to buy from the machine OEM. Those motors then are the ones that end up in the hands of recyclers who sell them for 80-90% off!

Basic rule: you get what you pay for.

"Will work for (the memory of) salami"

 

[Skogsgurra]

Bridges have been around for much longer time than electrical motors. But you do not build bridges if you are a biologist - or an EE. The less you know about a subject, the simpler you think it is. I would never dream of doing marine biology. Even if marine organisms have been along for a hundred million years or so.

Gunnar Englund

http://www.gke.org

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

 

[Bretina]

I see. Very wasteful to have so many motors get thrown away that way when they work just fine, even if for a while or for education. Like a used car and its parts for a hobbyist or for shop class at a vocational school. Many standardized ones could be rebuilt like car starters and alternators.

I try not to limit myself and instead be open minded. I know many important inventions have come about by accident to novices and cross field curiosity and collaboration.

Thanks for your advice.

Bretina
FL, USA

 

[Skogsgurra]

You may be right there. And nothing prevents you from doing those experiments and coming up with great solutions. What you need to understand is that it may take some knowledge and experience to get it right. There are also a few safety issues involved. Hire an EE and get it done with scrap motors if you think that saves the world and your R&D bill.

Gunnar Englund

http://www.gke.org

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

 

[OperaHouse]

Alomg with F=MA and you can't push a rope, I was taught that form follows function. Find a motor you would really like to have in a caatalog and get its voltage/current, weight and dimensions. Then look to see if you have one the same size in your stock of used. Size and weight are a good indication of power. We will just assume you are talking about DC motors. Apply a low voltage and see what you get for speed. If that is in the ballpark, upon cleanup determine an appropriate current from the wire size. Try it with an appropriate load for a half hour. If you can keep your hand on it without burning it just might work for you.

To be honest, half the people here couldn't spec a motor for an application if their life depended on it. They use whatever they have seenother people use in the past. If really chicken they order it 50% bigger. Sizing a prop to a motor always ends up as an experiment.

 

[Bretina]

Thanks very much! That sounds like a practical compromise to keep things moving forward. I can see you can appreciate that having a tight budget usually requires creative workaround solutions to at least get past the experimental working concept stage. Going to the high expense and time of hiring engineers to spec the whole thing out before it's sure to be viable seems too risky, when a few hundred dollars and some used parts will get us most of the way there. After that, then it makes sense to spend on engineering refinements.

Bretina
FL, USA

 

[jraef]

To be honest, half the people here couldn't spec a motor for an application if their life depended on it.

Well, I have no doubt whatsoever that Gunnar can spec out a motor, so by the process of elimination I that means you are talking about me. Looks like I'm doomed if my life ever depends on it....

"Will work for (the memory of) salami"

 

[Skogsgurra]

You don't need to take it personally, Jeff. I already did.
I think that we had better leave the actual specification to the specialist

Gunnar Englund

http://www.gke.org

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

 

[1gibson]

You want to save money? Find a market that upgrades the OEM motors (high end RC cars??) or a high volume market like automotive (windows, wipers, power seats) or other small appliances (cordless tools.)

All those are likely to be available as surplus, difficult but not impossible to find specs, and if everything works out perfectly the first time, available from OEM in higher quantities.

 

[waross]

Glad I didn't respond and push the ratio up to 2/3rds.
But I have to admit that I AM NOT capable of specifying a motor with these criteria, or even copying someone else.

We're planning to develop and ocean going autonomous data and specimen collecting submersible robot. I'm in charge of component procurement and I hope to mitigate the high R&D costs by scavenging used components to try out prototypes first.--
I've located a source for used electric motors but they are all unmarked except for the occasional voltage stamp. How can the other specs, such as amps, torque, rpm or even voltage be determined on these unmarked electric motors? Is there a machine to connect them to which tells the specs or are there shops that specialize in this? Also, I have a multimeter and a benchtop power source if this is typically done with these tools. If so, how?

Just a WAG but the motor that aims the camera may not be suitable for operating a grapple to retrieve a 500 lb or 1000 lb treasure.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Bretina]

Good idea about the surplus suppliers. I'll definitely look into those.

Being autonomous these will be let loose to signaling back data about conditions where they are. If it looks interesting, we'd signal it to collect a small sample. They won't be like the big, manned "Transformer" looking ones.

Bretina
FL, USA

 

[X49]

Just run it and slowly keep adding load until it starts to smoke. The rating will be this load less, let's say, 30%.

 

[Bretina]

I'm sure that won't be exact but close enough to know what specs to shop for later. What about the measure of load? Would attaching a torque wrench, starting with no resistance, then slowly tightening it until the motor smokes, give me the torque reading at that point - also less 30% of that reading?

Bretina
FL, USA

 

[OperaHouse]

And here I thought by bumping the number up I was being sensitive. Don't blame additional years of therapy on me. You were being hard on someone that only had to hook up two wires. If it looks like a duck and quacks like a duck, it's a duck. Although a researcher was a little more than perterbed with me when I called a voll a mole. Don't want either in my yard. In any project there are...... known knowns, known unknowns, and unknown unknowns. A little working data will tell you what is needed for a motor or maybe adjust the spec to something reasonable. The real reason for posting follows.

Buy a Turnigy 130A power meter for about $30 shipped. It is ideal for getting the numbers Watts, amp hours, peak values etc. I've seen resellers charging up to $130 for this same device, so it it is more than $30 keep looking. You will end up making it part of the final device after testing phase.

You will want your motors reliable. I have checked a lot of motors by monitoring brush current with a scope under a light load. Consistency is not the hob goblin of small minds. If you see a periodic anomolie in the waveform there is likely a winding or commutator problem.

 

[rhatcher]

Some of the suggestions here may not work. Car engine starters, power window motors, and many power tool motors are not rated for continuous duty and will overheat if used continuously. Unless the robot will be drifting with the current, at a minimum the propulsion motor will need to be continuously rated.

Also, since you are not requiring the motors to be watertight I am assuming that they will be located within the robot. This brings up the issue of cooling. Based on the motor efficiency, waste heat will be given off and will accumulate within the robot. At some point the temperature will rise to the point that the motors overheat. Another way to look at this is that most motors are rated for operation in a certain ambient temperature, usually 40C maximum. Operating in environments above this temperature will cause the motors to overheat.

 

[Bretina]

Thanks again. I'm going to look into the Turnigy 130A and see how it works.

Although they will be drifting at times, preparing for continuous operation will take care of both scenarios. Following you advice, we'll need to add some kind of sealed heat exchanging system to it. I don't think that will be a real challenge to do.

Bretina
FL, USA