Reeling Motor Project - Help Please

  • #1
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Hello,

I'm a engineering student currently taking Thermodynamics and we have this project for our finals which is a sort of reeling /towing device, the assignment consists in a reeling motor that has to tow a small car up along a slope, loaded with a certain weight, the team that is able to reel in the most weight in the shortest time will win the competition and have the maximum grade and extra credits for the semester.

The rules are:

You can only use 1 Peltier thermoelectric generator module that will deliver 12 volts to the motor of my choosing. No capacitors or energy storage devices. I could use a voltage regulator to rise the voltage but speaking to one of my professors he said that due to the fact the power is just a relationship between current and voltage, rising the voltage wouldn't really make a difference as the current would drop, so my best shot was to shop for a motor with good torque that would surely work under 12 volts in case the peltier module does not deliver its full capacity.

I had 2 options, and because I need to move the biggest load in the shortest amount of time, I had to look for a motor with a good speed/torque relationship that would work under 12 volts in the worst case scenario, but I read somewhere you can make a speed reduction arrangement to help torque like the one below:

Reducing Engine

So I went and bought two different motors,

One with high speed and comparably low torque (to see if I the reducing arrangement can help me get a better torque in the end.

BEMONOC Small DC Motor 12V High Speed 12000 RPM High Torque PMDC Motor for DIY Parts  (0.135 N.m)

And one with low speed and high torque, to test both.

Greartisan DC 12V 200RPM Gear Motor High Torque Electric Micro Speed Reduction Geared Motor Centric Output Shaft 37mm Diameter Gearbox (0.2157463 N.m)

But I was wondering if you have any suggestions as to how to improve this torque/speed relationship and get the best out of it, I really want to win this competition.

I would truly appreciate any information you can share with me in contribution to my project.

Thank you in advance and sorry for my grammar, English is not my first language.
 

Answers and Replies

  • #2
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You can only use 1 Peltier thermoelectric generator module that will deliver 12 volts to the motor of my choosing. No capacitors or energy storage devices. I could use a voltage regulator to rise the voltage but speaking to one of my professors he said that due to the fact the power is just a relationship between current and voltage, rising the voltage wouldn't really make a difference as the current would drop, so my best shot was to shop for a motor with good torque that would surely work under 12 volts in case the peltier module does not deliver its full capacity.
You are fully focused on the motor, and taking that 12V as a kind of absolute what will drop only in case the peltier is not on full capacity. It's not like that.

For example, a lead-acid battery commonly used in cars said to have 12V voltage. Actually, its voltage will be between 13V and 11V, but if you want to pull the maximal power, then it'll be around 6V (what is not practical - below 9V will most likely burst the battery in seconds, even the practical 9V what happens during startup is extreme).

I suggest you to focus on your Peltier first.
 
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  • #3
anorlunda
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Gears amplify torque but loose power. High gear ratios amplify torque but loose more power.

But a good design principle to follow is keep it simple. The more complexity you add, such as intermediate speed reduction, the more power you loose.

I agree with @Rive , if you can find better Peltier generators, that has the most leverage. Most of them make tiny amounts of power. Keep your focus on energy&power&time rather than RPM&torque&volts.

Can you let a string wind up on the shaft of your motor and pull the load up? That is a form of speed reduction that allows you to use a smaller power for a longer period of time, to achive the energy you need.
 
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  • #4
jrmichler
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Start with the Peltier generator. Measure the voltage vs current curve, and look for ways to improve it (better heat transfer). Locate the maximum power point, then find a motor designed to operate at that voltage and current. Then use @anorlunda suggestion of a string speed reducer. Use the thinnest string you can find, such as monofilament fishing line or sewing thread.
 
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  • #5
CWatters
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+1

You also need to figure out how points will be awarded. Is it better to pull a heavy weight slowly or a lighter weight quickly? Does one give you more points than the other?
 
  • #6
CWatters
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Perhaps consider a tapered drum on the winch to provide both good starting torque and high top speed?
 
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  • #7
Chronos
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This sounds like a good flywheel application, using it in lieu of a capacitor - assuming that is permissible under the rules as stated.
 
  • #8
berkeman
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You can only use 1 Peltier thermoelectric generator module that will deliver 12 volts to the motor of my choosing.
What is the heat source for your Peltier generator? What is the heat flux into the generator? What is the typical efficiency of the conversion to electrical energy? What power do you estimate you have to run the electric motor? Can you show us your calculations so far?

https://www.ebay.com/i/253473259913?chn=ps

s-l640.jpg
 

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  • #9
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This is the one that's set to be delivered next week, my project is due on the 23rd.
Aideenpeen peltier module 12v.
The heat source is a 100 ml alcohol burner, we have to design the burner, but that has been assigned to another one of my peers, although the way things are, suggestions wouldn't hurt as I'm the only one really concerned about designs and optimization. I've done some calculations, but I did them backwards as I started doing the diagrams for the load and time I wanted, just to check how much power I would need. But my professors and people here in the forum set me on the right path (to do my calculations based on whatever I can get from the module), but because I wont get them until next week I wont have that info until then, I ordered the motors because I live in central america and they don´t sell good motors here, therefore if I waited until I had the numbers from the peltier modules the motors would not have arrived on time, and that's the reason why I ordered the two different motors I posted before, instead of just one.

But for an estimate, I would be EXTREMELY HAPPY if I got 48W. 12v and 5.8 A max. It's risky because 48W is near the maximum current and voltage but we have also ordered two different peltier brands to see which one is the most efficient.
 
  • #10
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Start with the Peltier generator. Measure the voltage vs current curve, and look for ways to improve it (better heat transfer). Locate the maximum power point, then find a motor designed to operate at that voltage and current. Then use @anorlunda suggestion of a string speed reducer. Use the thinnest string you can find, such as monofilament fishing line or sewing thread.
Can I ask why is it better to use a thin string¿? Jusk for the sake of knowledge.

+1

You also need to figure out how points will be awarded. Is it better to pull a heavy weight slowly or a lighter weight quickly? Does one give you more points than the other?
I have been thinking about this, but I guess it would be a sort of relationship between the two, some sort of coefficient.

Can you let a string wind up on the shaft of your motor and pull the load up? That is a form of speed reduction that allows you to use a smaller power for a longer period of time, to achive the energy you need.
I don't know if It's permitted but I´ll definitely check.


Perhaps consider a tapered drum on the winch to provide both good starting torque and high top speed?
I'll do my research on this, thank you.



Guys, I just want to say, Thank you very much for your responses, I asked the same question in a couple of other forums and I did not get responses as knowledgeable as these. I can see you really know what you are talking about. I'm set to get the modules next week, I´ll get the calculations and I´ll go from there.
 
  • #11
anorlunda
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the assignment consists in a reeling motor that has to tow a small car up along a slope, loaded with a certain weight, the team that is able to reel in the most weight in the shortest time will win the competition and have the maximum grade and extra credits for the semester.
You could have a strategy to lift the heaviest load in one lift, or to make multiple lifts with a smaller weight for each trip. Which have you chosen? I'm going to assume a single lift.

If the lift was vertical, it would be easy to calculate the energy, just weight*distance. But on a slope, friction is likely to be very significant too. Can your car have wheels? What have you done to minimize friction?

Even without friction, you have another degree of freedom; time. I assume that "most weight in the shortest time " means that weight/time is the figure of merit. Correct? If no, then how will they calculate "most weight in the shortest time "?

No matter which motor you order, if you use the winding string, you can still experiment with cylinders of different diameter attached to the motor shaft. The bigger the diameter of the cylinder, the shorter the lifting time, but the less the weight capacity. Experiments, should point you to the optimum weight/time compromise.
 
  • #12
CWatters
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Take a look a reviews on Amazon. One warns it's easy to damage them by overheating.
 
  • #13
berkeman
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Take a look a reviews on Amazon. One warns it's easy to damage them by overheating.
The generators or the motors?
 
  • #14
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Take a look a reviews on Amazon. One warns it's easy to damage them by overheating.
Yes, we bought some heat sinks as well to control temperature, we will do some tests to try and reach a high temp near the max allowed by the device but no further.
 
  • #15
CWatters
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I was referring to the generators. Think the datasheet say absolute max is about 130c and an alcohol flame could be a lot hotter?

Not sure if there is a minimum cold temperature. Can you use dry ice?
 
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  • #16
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You could have a strategy to lift the heaviest load in one lift, or to make multiple lifts with a smaller weight for each trip. Which have you chosen? I'm going to assume a single lift.

If the lift was vertical, it would be easy to calculate the energy, just weight*distance. But on a slope, friction is likely to be very significant too. Can your car have wheels? What have you done to minimize friction?

Even without friction, you have another degree of freedom; time. I assume that "most weight in the shortest time " means that weight/time is the figure of merit. Correct? If no, then how will they calculate "most weight in the shortest time "?

No matter which motor you order, if you use the winding string, you can still experiment with cylinders of different diameter attached to the motor shaft. The bigger the diameter of the cylinder, the shorter the lifting time, but the less the weight capacity. Experiments, should point you to the optimum weight/time compromise.
It is a single lift.
We are going to 3D print the car, it is just a 0.4m2 square chassis with 4 wheels, and we are still trying to solve the friction issue because it is a 6 degree concrete slope, when I did the calculations on the diagram static friction only was 0.5 of the normal. But because we are using wheels, I'll go talk to my dynamics teacher as well to help me understand the benefits of wheels and friction and what will be the best material for the wheels, do you have any suggestions?
 
  • #18
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I was referring to the generators. Think the datasheet say absolute max is about 130c and an alcohol flame could be a lot hotter?

Not sure if there is a minimum cold temperature. Can you use dry ice?
Yes, we want to use ice on one side of the generator and the flame (possibly with the heat sink) on the other side, to max the temperature difference and get the max voltage. That will depend on the datasheet as you said.
 
  • #19
berkeman
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Yes, we want to use ice on one side of the generator and the flame (possibly with the heat sink) on the other side, to max the temperature difference and get the max voltage. That will depend on the datasheet as you said.
Do you have anybody on the team with an electronics background? If so, there is an important trick for the circuitry that you could place between the generator and the motor.

MPP converter...
 
  • #20
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Do you have anybody on the team with an electronics background? If so, there is an important trick for the circuitry that you could place between the generator and the motor.

MPP converter...
I'm actually the one they're relying on for everything regarding this project because of the four on the team I'm the only Electrical Engineering student, they are Industrial. I'm currently taking Fundamentals of Electrical Circuits so I have a basic understanding of everything for now. But whatever you suggest I will definitely learn how to do it if it will be useful.
 
  • #21
berkeman
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When you get a chance, Google the term under the Spoiler tag that I posted, and add in some extra search terms like the kind of generator you are using. You can increase the performance of your system a fair amount if you use that technique. :smile:
 
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  • #23
CWatters
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+1 to an MPP converter. Ive seen one used between solar panels and a motor on a solar powered model aircraft. The controller varied the pitch of the prop to keep the solar panel at the MPP. If you waved your hand over the panels the prop pitch changed.
 
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  • #24
Borek
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Two thoughts:

1. If you are afraid of overheating the Peltier, perhaps you can submerge it in a high boiling liquid, then the temperature won't go over the boiling point.

2. Keeping the cold end in a low temperature is important, but perhaps even more important is the ability to quickly cool it down back. Putting the element just in an ice block won't work, but putting it in a cold, low freezing liquid can be better (convection).

Just my $.02, not sure if these are worth the hassle. The latter is a direct effect of getting too hot while jogging in over 80 F :wink:
 
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  • #25
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Somebody else did half of the job already. Check this document:
http://www.asee.org/public/conferences/8/papers/3976/download
As it seems there will be a bit of mismatch between the output voltage and the motor specs.
Yes, very good data in there. While MPPT seems to make sense, I'm not sure it will be needed. The power curves look pretty flat, eyeballing within ~ 10% over a range of 1V ~ 1.5V? I would think the motor load could be matched to that pretty easily over a short term.

Those motors do appear to be very mismatched. That paper uses a somewhat larger sized Peltier (92W Qmax versus OP's 53W):

https://www.amazon.com/dp/B002UQQ3Q2/?tag=pfamazon01-20
https://www.amazon.com/dp/B078T7J3SF/?tag=pfamazon01-20

In the paper, they are only getting ~ 1/2 Watt and ~ 1.5 Volts out of it @ 50C delta, and an efficiency of ~ 1.5%. It looks like OP is using the INPUT POWER ratings, and expecting that as an OUTPUT POWER? But I don't think it works that way, the efficiency comes into play, and the output is far less.

OP might want to look for motors designed to run on a single AA battery and around 300mA?

Agree with @Borek on using liquid on each side. Not only will that control the temps, but provides good thermal transfer. You can buy silicone baking mats and cut them to size for gaskets. Maybe 3D print a holder (can 3D printing handle the temperatures?).

https://www.amazon.com/dp/B0725GYNG6/?tag=pfamazon01-20
 
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