# How can I control an electric motors speed?

#### A.C. Alden

Joined Apr 10, 2018
22
I'm at a stand still with an experiment I'm doing involving an electric motor with speed control. Everything was working fine until I actually put everything together and the contraption has a little to much friction for my 100 watt sewing machine motor to overcome. So I'm looking for a solution but I'm running into a major issue.

So basically I need an electric motor with like 1/2 hp or greater that I allows me to tune the speed with relatively fine control. I'm afraid to buy anything because I know it will probably not work the way I need it to (I need to be able to sloooowly turn up the speed to quite a few rpm)

If you know what type of motor I could pair with some type of speed controller I would be grateful.

Joined Feb 20, 2016
3,721
A universal motor is the easiest to control but you can use an induction 3 phase motor with a Variable Speed Drive.
Also, Brushless DC motors work well. Some washing machines have these.
If you can get an old treadmill that may be a good source of the motor and speed control.
Do you want variable speed or actual controlled speed so it automatically adjusts to suit the load changes?

#### Yaakov

Joined Jan 27, 2019
1,647
I'm at a stand still with an experiment I'm doing involving an electric motor with speed control. Everything was working fine until I actually put everything together and the contraption has a little to much friction for my 100 watt sewing machine motor to overcome.

So basically I need an electric motor with like 1/2 hp or greater that I allows me to tune the speed with relatively fine control.

If you know what type of motor I could pair with some type of speed controller I would be grateful.
The jump from your sewing machine motor to a 1/2HP motor is quite large, how did you decide that?

#### Alec_t

Joined Sep 17, 2013
11,878
What rpm range do you need? A small motor with a reduction gearbox might be better than a big motor running at near minimum speed.
What are you using the motor for?

#### A.C. Alden

Joined Apr 10, 2018
22
Well basically im trying to spin a really large ball mill. I need to be able to run it very slow like one rotation a second or all the way up to like 1800rpm (I don't know if ill go the high but would like the option)

I have maybe a 300$budget. More it absolutely necessary. I thought the 100 wat sewing machine motor could handle it. It was cheap and came with speed control. #### Yaakov Joined Jan 27, 2019 1,647 Well basically im trying to spin a really large ball mill. I need to be able to run it very slow like one rotation a second or all the way up to like 1800rpm (I don't know if ill go the high but would like the option) I have maybe a 300$ budget. More it absolutely necessary.

I thought the 100 wat sewing machine motor could handle it. It was cheap and came with speed control.
It looks like your best direction is a treadmill motor (I believe it was mentioned earlier). It is very commonly used for tools and even ball mills. Videos about the idea abound, and you might just be able to get one free if you can find someone with a disused treadmill. Here is a thread on AAC about controlling one.

If I was doing this, I’d been go that way. It seems most sensible.

Joined Jul 18, 2013
22,343
We have a site here called Kijiji (Swahili for Market) I believe owned by ebay, but there is no posting fee's etc and there is a T.M. going free at least once a month where someone just want to get rid of it.
Every area in Canada has its own local Kijiji, so easy for pick-up.
Max.

#### shortbus

Joined Sep 30, 2009
8,317
Well basically im trying to spin a really large ball mill.
Define, "very large". As a machinist my whole adult life, ball mills come in many sizes, what you might consider large might not be what you think is large. We don't have a clue to what your experiment and contraption is. Explain what you're trying to do, it will get you better answers.

#### Tonyr1084

Joined Sep 24, 2015
5,701
I thought the 100 wat sewing machine motor could handle it. It was cheap and came with speed control.
Well, considering that one HP is 745.7 watts - I'd say a 100 watt motor is 1/7 HP (roughly speaking).

I've scrapped out half a dozen treadmills. They typically come with 2 HP to 2 1/2 HP DC motors. Using the speed controllers that come with the machines, having variable speed is easy if you can get a hold of a treadmill being given away. I have a TM motor and speed controller on my bandsaw right now. And when I cut with a slow setting if I bog down the motor amps up to maintain that same RPM. It's not instantaneous but is is good enough.

Why a variable speed on a bandsaw you ask? Because the OEM motor went bad and I didn't feel like spending $185 for a new motor. With a little welding fabrication I manufactured a bracket that would hold the motor in the correct position. Turns out the pulley on the end of the TM was exactly the same as the OEM pulley. So I didn't even have to change that. Just mount the motor, mount the controller underneath and put a "Start" button by the power switch along with an adjustable potentiometer to control speed. So if I'm cutting plastic I don't want to run the blade too fast or it can melt the plastic. #### Yaakov Joined Jan 27, 2019 1,647 I have a TM motor and speed controller on my bandsaw right now. And when I cut with a slow setting if I bog down the motor amps up to maintain that same RPM. It's not instantaneous but is is good enough. And, you can tell how many miles you've cut! #### Tonyr1084 Joined Sep 24, 2015 5,701 #### GetDeviceInfo Joined Jun 7, 2009 1,749 The question of 'how large is large' is valid. I've installed mills that mill paint, run with 50hp motors. One problem you'll encounter is that initial acceleration must have enough torque to turn the mill and contents until the balls roll. On one mill we had to 'rock' the mill several times before it gained enough rotation to free the balls. #### MisterBill2 Joined Jan 23, 2018 7,977 I also wonder about the size of the ball mill, and in addition, 60 RPM is not slow. And 1800 RPM for a ball mill is far out of control and i an runaway condition. As all ready commented, it is the starting torque that is the problem. My suggestion is an induction motor and a mechanically variable drive to start slowly and then go faster. Check out the reduction system on an older "HARTRIDGE" fuel injection pump tester. That had a very wide speed control ratio. #### shortbus Joined Sep 30, 2009 8,317 I've installed mills that mill paint, run with 50hp motors. I may be wrong about this but I thought the TS was talking about a ball mill cutter, not a ball mill to reduce material, like in a paint mill. #### MisterBill2 Joined Jan 23, 2018 7,977 Once again we have a lack of information leading to a stream of guesses. I had not considered a ball type milling bit because they are used in milling machines that usually have a built in motor, OR, such a bit may be used in a router device, which also includes a motor, sometimes with variable speeds. Ball mills of the rotating barrel type come in sizes from hand-carry able to truck drive-through. So clearly we need a bit of additional information to be able to deliver anything beyond guesses. I do own a thing called a mortise cutter that could easily utilize a bit such as shortbus shows to produce holes in pieces of wood. I thought that it could be used as a drill press, and the price was right. Unfortunately it would not work very well as a drill press. #### MaxHeadRoom Joined Jul 18, 2013 22,343 Well basically im trying to spin a really large ball mill. I need to be able to run it very slow like one rotation a second or all the way up to like 1800rpm (I don't know if ill go the high but would like the option) I thought the 100 watt sewing machine motor could handle it. It was cheap and came with speed control. One thing pretty much for sure, a 100w motor won't cut it! The 2.5hp T.M. and controller should be closer to it. Max. Thread Starter #### A.C. Alden Joined Apr 10, 2018 22 Thanks for all the reply's and I apologize for lack of information. Basically I'm looking for help picking out a motor and a speed controller that I can use for various projects and experiments not just a ball mill hence the reason for it going up to 1800 rpm BUT I'm not worried about it being capable of attaining even higher speeds just as long as I can control the speed. By control the speed I mean very fine speed control so I could essentially run the motor at 1 rpm or maybe 6 rpm... Also if the size of the gear is smaller than the gear on the contraption the rpms are reduced and I think torque is increased. I've ran into information that states that motors with capacitor start cannot have their speeds controlled. Ive run into other information that states that only certain speed controllers are compatible with certain types of motors but I have trouble finding the motors for sale. So basically the goal here is a specific motor type and speed controller type that will work together to produce a wide range of relatively fine control of the speed. I'm going to look at treadmills on craigslist because that might actually work but I would prefer a motor that I could custom build gears for to connect with custom length of bike chain. #### MaxHeadRoom Joined Jul 18, 2013 22,343 The T.M. style motor and controller is a favorite due to the necessity of a T.M. to maintain RPM. I like the Johnson brand of T.M. motors, Chinese, in spite of the name!. The better controllers, especially for low RPM are the MC2100's, you will need to put together a pot control as it requires a low level 20Hz PWM signal to run. There are 555 based ones out there. I have also put together one for the MC2100 using a 8 pin microchip, and stop start P.B.'s. Max. #### shortbus Joined Sep 30, 2009 8,317 By control the speed I mean very fine speed control so I could essentially run the motor at 1 rpm or maybe 6 rpm. I very much doubt you'll find any motor ,short of a gear motor that will like going that slow. That is the reason they make gear motors and things like belts, pulleys, chains and sprockets. You still haven't addressed what you're trying to do. #### Bernard Joined Aug 7, 2008 5,740 If in US, www.surpluscenter.com, has gears, chain, T.M. motors, & controllers. One HP as low as US$
29.95. Maybe a 100 : 1 double reduction with attached slotted disc for feed back control. In a smaller system at very low speed'
motor advanced like a stepper following code disc.