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 Post subject: Homemade Multi-Drill
PostPosted: 07 Jul 2018, 09:49 
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Joined: 07 Jul 2018, 09:48
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Hi,
I'm thinking of making a multi drill for wood drilling, that uses anywhere from 6 to 9 9V or 12V DC motors. These motors would be wired in parallel, with one battery source. I'd mount a drill chuck on each of the motors shafts for a drill bit. Now, I need a little bit of help from you. Do any of you have an experience in doing such a project?
My main concerns are drilling torque so that I could drill holes effortlessly in about 5 centimeter thick wood frames. Also, Another concern is battery life and how many volt batteries should I get? With same voltage as the motors? Are DC motors prone to overheating by working close to their full potential? My goal is to have reliable and long-lasting contraption for drilling.

Thank you very much, I wish you all a good day!


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 Post subject: Re: Homemade Multi-Drill
PostPosted: 08 Jul 2018, 04:05 
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Joined: 07 Jul 2018, 09:48
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I was thinking anywhere from 4-6 drills, spaced about 5 centimeters apart. I would like to be able to use smaller drill bits, like 4mm.
Maybe batteries are more of a hassle than I thought. After more thinking about this project, the best option would be 220V power supply rather than battery, since this machine would only be needed in garage. In this case, a transformator should be wired before the circuit (motors) and maybe bridge rectifier. Would I need anything else, like voltage regulator? My main goal with this project is being as straightforward and simple as possible, with enough DC motor torque to drill thicker pieces of wood and without motors overheating but still as cheap as possible. Don't need motor speed control, torque control or any kind of extra, except for one simple switch.
For mechanics, framing and other things is not a problem, can get anything practically for free.
On another forum one guyf recommended this DC motors: https://www.ebay.co.uk/itm/10-1-Gearmotor-with-Encoder-DC-24V-1000RPM-Encoder-Gear-Motor-37Dx49L-mm/183147703801
https://www.ebay.co.uk/itm/Electric-High-Torque-Turbo-Worm-Gearbox-Geared-Motor-DC-Motor-12-470RPM/182743834655?clk_rvr_id=1590899362551&afsrc=1&rmvSB=true

Is anything even cheaper viable to have reasonable drill speed and torque for 4-5mm drill bits?
Here are the pictures of one similar machine:


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 Post subject: Re: Homemade Multi-Drill
PostPosted: 08 Jul 2018, 04:21 
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Joined: 01 Jun 2013, 09:05
Posts: 677
It won't work,

If it was as simple as you assume why do you think a hand drill has a gearbox?

Batteries won’t last long this is just a guide and others on here may give you more info.

Motor direct to drill chuck:
Motor speed to fast.
If you reduce the speed no torque.
You could use pulse width modulation, but it still won't be much use.
The larger the hole the higher the torque.
Motor direct to chuck is the same as a Dremel, OK at high speed with very small drill sizes.
You don't specify drill sizes.
High speed burns out drill bits at a high rate.
You are looking at three motors all drawing high current (variable with hole size)
Do you intend to hold the motor or put them in drill stands?
If you intend this to be like a production line, then are the motors running all the time or on and off.
It goes on but the question you ask is way to simplified.
DC motors need maintenance brushes wear out that’s why industry went to inverter drives with AC motors.
NB slowing the motor reduces internal air cooling, so it increases over heat.
Just a quick answer (no further comment) I have never done a project like this so its just my thoughts.
NB speed control won't remove the need for mechanical gearing.
Also speed control will create heat and reduce efficiency.

NB without closed loop control the speed of the motor will vary with torque.
So it will slow down when drilling and speed up in free air.
So you won't be able to set the drill speed and then drill a hole.

Regards
M. Gregg

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 Post subject: Re: Homemade Multi-Drill
PostPosted: 09 Jul 2018, 02:45 
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Looking at your links,

The motors you show are motor/gearbox drives.
You are not putting the chuck on the motor, you’re putting it on a gearbox.
Assuming there is enough torque and the speed is correct it might work.
The battery idea may also work based on Ampere/hour eg if a battery was 10 Ah then you could draw 1 amp for 10 hours just as an example. But you would need to know about application and if these motors can do the job I have no idea.
The motor current is just adding them all together and work out how long the batteries would last between charges.
Something like car lead acid batteries would work but you still have to charge them, if you use a power supply you need smooth DC just a rectifier won't do it the ripple will damage the motors.

Your initial idea of batteries will work, but you still need more information about torque.
You might buy the motor units and find them not up to the job, so you need advice from someone who has built this kind of thing.

Link:
https://en.wikipedia.org/wiki/Ampere_hour
https://www.allaboutcircuits.com/textbo ... y-ratings/

You could use SMPS but the main thing is how strong are the gear boxes? If they have plastic/nylon gears etc.

Interesting to hear ideas from other members.
Just curious, what will you use this for? What function?


Regards
M. Gregg

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 Post subject: Re: Homemade Multi-Drill
PostPosted: 09 Jul 2018, 04:32 
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Remember,

the starting current on a motor is higher than the running current, so you must make allowances for the starting current X the number of motors.

If I was doing this I would decide on the motor/gearbox unit and buy one. Test it with a chuck attached and measure the starting current and drilling current under load. Then add about half again for the max power used to multiply by the number of motors. The obvious advantage to the batteries is they can deliver high current at start up. But you might be able to get a SMPS that will do it.
Or once you know the current delivery required you can post again and work out a DC supply.
The main thing is making sure the motor/gearbox drive will last and handle the torque required. There is no accounting for if a drill jammed in operation. A DC supply can have current limit, but in this case its probably better to protect each motor individually to stop it burning out. Its probably overkill but worth mentioning.
You could use solid state fuses that auto reset. (nothing like over engineering :D ).


Regards
M. Gregg

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 Post subject: Re: Homemade Multi-Drill
PostPosted: 09 Jul 2018, 10:38 
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Joined: 07 Jul 2018, 09:48
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M. Gregg wrote:
Remember,

the starting current on a motor is higher than the running current, so you must make allowances for the starting current X the number of motors.

If I was doing this I would decide on the motor/gearbox unit and buy one. Test it with a chuck attached and measure the starting current and drilling current under load. Then add about half again for the max power used to multiply by the number of motors. The obvious advantage to the batteries is they can deliver high current at start up. But you might be able to get a SMPS that will do it.
Or once you know the current delivery required you can post again and work out a DC supply.
The main thing is making sure the motor/gearbox drive will last and handle the torque required. There is no accounting for if a drill jammed in operation. A DC supply can have current limit, but in this case its probably better to protect each motor individually to stop it burning out. Its probably overkill but worth mentioning.
You could use solid state fuses that auto reset. (nothing like over engineering :D ).

Regards
M. Gregg


Thank you very much for your contribution to this thread.

After prolonged research, I'm set on this DC motor: https://www.banggood.com/775-Gear-Motor-DC-12V-36V-3500-9000RPM-Motor-Large-Torque-High-power-Motor-p-1091058.html?rmmds=detail-top-buytogether-auto__2&cur_warehouse=CN
This one is used in most battery powered drills, usually on 24V.
I'll be using 6 of these motors, so if they are connected to 24V one motor draws 0.16A, then 5x0.16=0.8A with a deviation of a few Amperes.
Onward, I've been looking and have been recommended this power supply: https://www.alibaba.com/product-detail/5V-12V-24V-48V-AC-DC_1705389176.html?spm=a2700.7724838.2017115.1.b3c83ab4qLUWpu&s=p
Now this supply has output current 2.3A-16A, does this mean it's not compatible with motors?
I've got another question; if power supply has for example output voltage 9-40V, does this mean that if I buy the motors (link), where voltage is 12-36V, that power station will fry the motors with full voltage or does it regulate it?

Thank you,
L


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 Post subject: Re: Homemade Multi-Drill
PostPosted: 10 Jul 2018, 05:29 
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Joined: 01 Jun 2013, 09:05
Posts: 677
Quote:
I'll be using 6 of these motors, so if they are connected to 24V one motor draws 0.16A, then 5x0.16=0.8A with a deviation of a few Amperes.


Remember building this is at your own risk so this is only a rough guide.
Remember the specification is showing running current, not starting current or current under load, so its going to be more that the specification says in operation! So you need to look at the starting and current under load then multiply this by the number of motors.

NB these are just motors not motor/gearbox drives so you are putting the chuck straight on the motor shaft (min speed 3500 RPM).
I hope you know this means there may not be enough torque, but I assume you have other input from someone that's used them.

Also min-max speed stated you will be running the drills at minimum speed of 3500 RPM but higher on 24V. The power supply doesn't know what the max voltage of the motors are so if you turn up the voltage past the spec the motors will go faster and eventually burn out. So you are in control and you are setting the voltage, the motors will draw whatever current they need to get to speed. If they stall or jam then the current limit will not save the motors it should protect the power supply. The reason is the power supply is supplying total current, each motor draws only a small % of the total so burn out current for one motor will still be within the power supply max current spec.


The DC voltage is quoted as 12-36v and the speed 3500-9000 RPM so it looks like and its only a guess. The speed at 12V is 3500RPM and will increase up to a Max of 9000 RPM at 36V.


The Current of a supply is the maximum current you can draw off it without burning out the power supply.

Ie if a power supply is quoted at 10A then the "Load" (your motors) will draw whatever current they need to operate if they draw 2 amps then that's OK if they draw 12A then the power supply will burn out. So as long as the power supply can put out more current than you need its OK but less than you need it will burn out.

The 24V model of the power supply you link to is max rated at 4.5A so as long as you don't exceed this it should work.
But if the total starting current exceeds the power supply current then the SMPS will shut down in current limit.
So your buying the model with a set voltage and set current so if its a 24V then it has 4.5A.
Voltage is slightly adjustable in the spec to Quote 21.6 ~ 26.4V probably to allow for variation from 24V.

If you put more voltage across the motors than they are designed for the motors will burn out

Hope this has been some help.
You need someone who has one of these working so you can check the motor type they have used.
Without that its difficult to say what the outcome will be under load.
I'll let someone else have an input so you can get other ideas.

Regards
M. Gregg

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