Treadmill motor torque


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    Default Treadmill motor torque

    Hi, I'm pretty new to this. I need help with my treadmill motor setup. I hope this is the right forum.
    I have a wood lathe with a treadmill motor with the following spec and a MC-60 control board driving it.
    1.75 HP Continuous Duty @ 90 VDC
    Amps 15
    4200 RPM @ 90 VDC

    I believe the AC motor was 2hp but might have been 1hp.

    My issue is that it definitely bogs down/stops under load. Load meaning I'm taking a fairly heavy cut. It can turn my pieces no problem. I need it to be able to handle a log say 10" by 20".
    I know that that 1.75 hp DC is by no means comparable to 1.75 HP AC. But I thought it would have more.
    My question is,
    a) does this sound right? or would you expect this size to work? i.e. perhaps the problem is in the board
    b) if I get a bigger motor say 4 HP DC would you expect that to work and would that be safe for my MC-60 board or would I need a new one.
    Any thoughts or advice would be greatly appreciated.
    Thanks
    Raif

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  2. #2
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    Default Re: Treadmill motor torque

    Hi,
    treadmill motors rely on current to produce torque. Provided you have a big enough driver and power supply the treadmill motor will
    keep producing more torque until it overheats and blows up.

    I think your problem is that the motor is rated at 4200 rpm so it will have modest torque.

    Power= torque x rotational speed

    I calculate in metric units so I will stick with them....if your a Yank....too damn bad!

    1.75 hp = 1330W (hp x 760)
    4200 rpm = 439.8 radians/sec (2 x PI x rpm/60)
    torque =1330/439.8
    =3.02Nm

    3Nm is pretty modest for a spindle. If you use a gear or belt reduction the torque increases but speed decreases while power stays about the same.
    I suspect that you are not using the power that your motor has very well.

    Craig



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    Default Re: Treadmill motor torque

    Hi Craig,
    Thanks for reply, yea, I'm a Yank. I think... But I don't really understand much of that anyway . It seems that torque is inversely proportional to RPM given a constant power. I generally operate at between 500 and 3k RPM, but would be roughing out a log at <= 1000 RPM. I also have a step pulley system ( the old way speed was modified ) I think it goes 2", 3.5" 5" on the motor and reverse on the spindle. I have it set at 2" motor 5" spindle.

    so by using your equation (verified on the internet )
    at max RPM I have 3.02Nm
    at ~1000 RPM I have 12.7Nm

    I'm looking at another motor that is 3170W and 5225 RPM (max). It would have
    at max RPM 5.79Nm
    at ~1000 RPM 30.3Nm

    generally wood lathes come with between 1-3 HP AC motors. They tend to turn at 3500 RPM and use various techniques to change the speed. But I think it's typically mechanical. I don't know if that changes anything. If all things are equal then there shouldn't be much difference between the AC or the DC. I suspect they are not. The big one would be how is the speed changed. I know older models of wood lathes would use step pulleys and clutches and such. The controller for my dc motor, I believe, cuts the voltage on and off in order to reduce the speed, so full voltage full time would get the max RPM.

    So here's what I don't know
    1) does the speed modification technique effect the torque
    2) give 1, which I believe is the case and given a DC motor, which variable speed controller would be best for my application
    3) how much torque does one need to turn a decent log. If I really just need say 20Nm and I can get 30.3Nm from the second motor, minus inefficiencies of speed variation, should that be sufficient?
    4) will a larger motor fry my MC-60. The Treadmill control boards sold on ebay say nothing about how much ... current? they can take. If this does fry my board, how would I know what kind of controller board to get?

    Thanks for all the help.
    Raif



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    Default Re: Treadmill motor torque

    Hi,

    at max RPM I have 3.02Nm
    at ~1000 RPM I have 12.7Nm
    If you use a 4:1 gear reduction yes that is about right. If you rely on just the speed control then NO its not correct.
    If your speed control can produce 15A and your motor produces 3Nm of torque at 15A, that's it, that's all there is.
    If you use the speed control to reduce the spindle speed to 1000 rpm it will have the same torque, namely 3 Nm
    because the current output of the speed control is maxed out at 15A.

    at max RPM 5.79Nm
    at ~1000 RPM 30.3Nm
    Yes, if you use a gear or belt reduction only.

    1) does the speed modification technique effect the torque
    Torque is proportional to current, speed is proportional to voltage. There are different ways for electronic controllers to produce
    a variable voltage, one method is called Pulse Width Modulation, and another very common method with these motors is
    called a Phase Controlled Bridge.

    With either of these techniques the controller will limit its current to protect itself. If two controllers using different control
    techniques both produce 15A then your motor will produce 3Nm torque with either of them.

    There are pros and cons for each technique but from the point of view of torque there is no difference....15A results in 3Nm.

    Maybe you should look at an AC servo. At 2kW plus they tend to have rated speeds of 1500 rpm but with a lot higher torque and may be
    better matched to your lathe. They have a servo drive that is direct connected to the AC line. Above 2kW most of them require
    three phase input.

    For example:
    https://store.dmm-tech.com/products/...ac-servo-motor
    11.5Nm rated torque with a short term overload of 28.7Nm and a rated speed of 1500rpm. You'd need the servo drive that goes with it:
    https://store.dmm-tech.com/products/...nt=20981907526

    Craig



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    Default Re: Treadmill motor torque

    DC motors produce maximum torque at zero RPM.
    See this for a detailed explanation. and where the normal operating point is in order to safely operate the motor.



    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default Re: Treadmill motor torque

    Ok, good stuff. Unfortunately my brain is reaching maximum velocity. So break it down for me folks.
    It sounds like my current motor will give me 3Nm. It also sounds like that's likely to happen at the lower speeds. So if I get the 4.25 HP motor that will provide 5.9Nm almost double. So that seems like an improvement, but would it be significant? If I were to mess with the pulleys, the ones on the spindle are pretty much fixed, but I could put a much bigger one on the motor. Do you think that would be a worth while modification?
    Regarding the AC servo motor, that's considerably more expensive. I can get the 4.25 HP motor for $70, $100 after shipping, plus I already have my MC-60 control board all setup.
    I will say this, I tried running at a very low speed, and it seemed to bog down even faster, I think/wonder if momentum plays a factor there.
    One concerning thing is that you mentioned "if your board provides 15A" the new motor would be 25A. I'm hoping that the MC-60 will rise to the occasion. The board and the motor were purchased separately and thus are from completely different machines. I have no idea what my board will produce. None of the descriptions of TM controller boards seem to give any info about that.

    Thanks for all the help
    Raif



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    Default Re: Treadmill motor torque

    Hi,

    It sounds like my current motor will give me 3Nm. It also sounds like that's likely to happen at the lower speeds. So if I get the 4.25 HP motor that will provide 5.9Nm almost double. So that seems like an improvement, but would it be significant?
    Is it significant, almost double the torque...I would say so. I would almost certain that the current required to develop the extra torque and power will be almost double
    too. I suspect your controller will max out and probably so would your power supply. Unless the controller and power supply can deliver the higher current then
    a new motor would probably be no better than what you have got.

    I think you would get more benefit by fitting a decent 2:1 or 3:1 gearbox.

    AC servos are not cheap but they are very torque and power dense, that is to say they produce the most torque and power for a given size of all electric
    motors.

    I have a second hand Allen Bradley 1.8 kW 3500rpm 6.2Nm (cont) servo and drive as a spindle motor on my mill....it works a real treat.
    While it says 1.8kW it really 'punches above its weight' whereas most motors you'd swear are only producing half the name plate power.
    'This is a 1hp motor so why is the f..%#^&&%%$ thing producing such pi...%^&*& all power!!!!' Not so with a servo.

    Another possibility that you might consider is a three phase induction motor driven by a decent VFD. The VFD gives you pretty good speed control
    and there are plenty of three phase motors of 1800 rpm (synchronous) or about 1725 rpm if you include slip. A good 2.2kW (single phase input)
    VFD, like a Hitachi will cost about $300.

    Craig



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    Default Re: Treadmill motor torque

    Yes, I think I found the root of my problem. The controller board ( it's a combo speed and power converter ) is rated at 1000W so right there I'm loosing almost a 1/4 of my power give the 1300W motor. It also means that a new motor will do nothing for me with out a new board. Seems most Treadmill controllers are lower wattage.
    So I'm looking at pieces parts. I can get a nice speed controller for cheap I found one which takes 10-55V in and is rated at 40A continuous 60A max. And it's only $15. But I can't really find proper power supplies. I don't think I'm searching for the right terms. There are also a one or two all in one boxes such as this one which is 120v in 90-130VDC up to 4HP. it's not so cheap and it's not very nice looking. I would almost rather build my own.
    https://www.ebay.com/itm/120-VAC-To-...QAAOSwAmVck46n
    I'm interested in your opinion, do you think I should go with the "all in one" or do you think putting together the parts should be do-able? Do you have any keywords I could/should use for searching for the power supply?
    Thanks,
    Raif



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    Default Re: Treadmill motor torque

    Also I'm not seeing, people saying you can take $5 bridge rectifier, plug it into the wall and use that as power. Then take the out put of that and feed it to one of those $15 speed controllers. This seems odd since it's basically so simple. Any thoughts on this would be appreciated too.
    Thanks



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    Default Re: Treadmill motor torque

    Hi,
    I think that you are trying to get a 4hp spindle for cheap......and you may succeed but with shortcomings.

    If you want a power supply that can manage 4hp, that's about 3kW. That is a lot to ask of a domestic supply. With the
    inevitable power factor correction value you'll be looking at 20A minimum from a 230V supply. If you have 120V only then
    double it, and some. Does your domestic supply have that sort of capacity?

    That all-in-one box is almost certainly a phase controlled bridge, that is two thryistors and two rectifiers in a bridge arrangement and probably
    another rectifier as a freewheel diode. The output WILL NOT be isolated from earth. Its not really an issue, many motors of this type are driven
    this way.

    If you are thinking of making your own I assume that you are familiar with power electronics? If not then this is not the right project to take on. If you
    get it wrong then non-isolated line voltage will appear on the frame of the motor with very definite safety implications.

    Much of the design expertise that goes into these devices are circuit ideas and techniques that improve safety and reliability, and most are far
    from obvious and are not documented. To make a safe and reliable device requires skill and experience....do you have it?

    Have you given any thought to and/or researched a VFD and a three phase induction motor? A VFD hooks direct to the AC line, no power supply
    required. They will drive three phase motors pretty damn well. In truth a VFD really requires an 'inverter ready' motor but any well and quality constructed
    three phase motor will work OK.

    Craig



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    Default Re: Treadmill motor torque

    The MC-60 is also a SCR controlled bridge, except it also includes current limit/ ramp up features etc of which the el-cheapo versions do not..
    The better versions are PWM such as MC2100 but these also have non-adjustable current limit, ramp up etc.
    For a DIY PWM drive , it generally requires some intelligent controller such as Microchip or Arduino etc .
    The advantage of DIY you can incorporate Bi-directional use and RPM indicator etc.
    Al.

    Last edited by Al_The_Man; 12-24-2019 at 03:57 PM.
    CNC, Mechatronics Integration and Custom Machine Design

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    Default

    Hi, so I'm not trying to get something for cheap. I'm trying to build a workable solution, with a configuration I like, for as little as possible. So I don't need 4hp. I have effectively 1.25 hp and it doesn't quite have enough torque. At first I thought well hell, I can get a much bigger motor for cheap, that should take care of the problem. It turns out my controller is the bottle neck first.
    So you ask if I have the expertise. This is how I build expertise or at least working knowledge. Through a combination of necessity and obsession. Its how I learned to be a cabinet maker, entrepreneur, and software engineer. It's non traditional I know. But I enjoy it.
    Currently, my mc-60 is the bottleneck. They only produce 1000w. My motor is 1300w. I've looked at the mc2100 but I can't find any info on how many watts it produces.
    I'm not fixin to short out a leathal dose of voltage. But the spc and rectifier just seems scary. I saw a cat use a 24v power source then use a step up... Thing, to output 45v. He was getting half expected rpm on the 90v TM motor he was driving with it, but I don't really understand the process yet and I question whether he will get the necessary wattage/torque. I would think the 24v power source would have to be 1000-3000 watts, but maybe the step up somehow multiplies the wattage.

    I understand that this is y'alls wheelhouse, that you have studied probably for year to understand this stuff better than I ever will. I don't mean any disrespect. I'm just trying to build up a working knowledge in one little area. Like my boy Fred said,that which does not kill me makes me stronger, and while he and I are a bit dangerously reckless, I have found in my life that endeavoring to understand anything is always a net benefit... If it doesn't kill me.
    Thanks



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    Default Treadmill motor torque

    I found a Dart speed controller on eBay for $50 to run my DC treadmill motor.
    I got a 253g-200e 2hp enclosed.

    The original 1/2hp on my wood lathe stalls easily under load. I’m hoping the Dart plus treadmill motor will be better, but I haven’t had time to install it yet.

    https://www.dartcontrols.com/product...speed-control/



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    Default Re: Treadmill motor torque

    Hi,

    So you ask if I have the expertise. This is how I build expertise or at least working knowledge
    Understood.

    Designing and building your own controller is a big undertaking and without serious power electronic experience I wouldn't
    recommend it. For some years I worked as a service technician on industrial welders/plasmas etc. I've seen plenty
    of apparently well designed and built power electronics blow up.....and I literally mean 'blow up', it can be spectacular!!.

    I would think the 24v power source would have to be 1000-3000 watts, but maybe the step up somehow multiplies the wattage.
    No, if you step up the voltage by double the current halves and so the power remains the same.

    IF....If you were to make your own controller it would be a safety advantage to isolate the controller from the supply.
    That would require a transformer of 1500VA for your 1.25hp motor or 3500VA for your 4hp motor. Just the
    transformer alone is going to blow your budget.

    Do yourself a favour and look on Y-Tube for info about VFD's. You'll be impressed.

    Craig



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    Default Re: Treadmill motor torque

    The ones I have put together, only the Mosfet H-bridge is live to mains, the low voltage is isolated via a small LV control transformer for the control circuit and opto isolators between control and bridge.
    It is based on Tahmids blog Tahmid's blog: Using the high-low side driver IR2110 - explanation and plenty of example circuits
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default Re: Treadmill motor torque

    Hi Al,
    I've had great success with these isolated gate drive ICs:

    http://www.ti.com/product/ISO5500?ke...-EN-everything

    They require isolated DC-DC supplies but they can now be had for under $10 each. This particular IC can accommodate +15V, -15V supplies for switching
    IGBTs where a pronounced negative gate voltage is indicated to overcome reverse Miller conduction. I have used these ICs to switch highside IGBTs up to 150A,
    with 4 in parallel for a 600A welding current regulator.

    The ICs cost only about $10NZD ($6USD) each delivered....hard to beat. Not so many years ago this would have taken a big design effort with bootstrap
    capactiors and/or transformer gate drives and/or opto-isolators and still be short of the UVLO and DESAT features!

    Notwithstanding the advances in technologies such as these ICs would you recommend to OP that he persue a DIY controller be it phase controlled
    bridge or PWM?

    I think his spindle problem could be solved very handily with a VFD and a four, six or eight pole (two pole pair, three pole pair, four pole pair)
    induction motor. A $300 Hitachi or Delta VFD being a cut above the cheapest Chinese offerings is still good value for money. Provided he can
    find a second hand induction motor of good quality with good insulation values my experience shows they run on VFDs OK.

    Craig



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    Default Re: Treadmill motor torque

    The VFD solution would definitely work, but I gathered that the OP want to make use of his T.M. DC motor, The use of one of the KB DC motor drives would likely solve the problem, the Triac control versions are compatible with the MC-60, but has the advantage of current control settings etc, however.
    Al..

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default

    Quote Originally Posted by jfong View Post
    I found a Dart speed controller on eBay for $50 to run my DC treadmill motor.
    I got a 253g-200e 2hp enclosed.

    The original 1/2hp on my wood lathe stalls easily under load. I’m hoping the Dart plus treadmill motor will be better, but I haven’t had time to install it yet.

    https://www.dartcontrols.com/product...speed-control/
    Hi, please post back if you get it hooked up. One thing I've been seeing with these controllers is that they'll give you 1hp @ 90vdc and 110vac or 2hp @180vdc and 220vac. My motor is 90vdc so I don't know if it would give me 2hp even if I hooked it up to 220. Which is frustrating.
    But let me know how it goes!



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    Default Re: Treadmill motor torque

    Your limit with the 90v motor is around 120vdc.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default

    Quote Originally Posted by Al_The_Man View Post
    Your limit with the 90v motor is around 120vdc.
    Al.
    Thanks for the replies folks, despite my rather odd rant
    First re vfd's my understanding is that they are 3phase. So in the us I can wire up a 110 or 220 circuit with whatever amps I want (within reason), but three phase is used only for industrial purposes. You'd most likely have to have the electric company come out and put a transformer on the pole and run it to your shop. I have actually gone through that dance before and it's not fun (long time ago at a proper shop).
    Second, I'm messing with the TM DC motor because I'm pretty close and I just don't feel like ramping up on all the domain knowledge necessary to go down another route.
    Third, there are two paths I'm considering currently. 1) take a cheap triac scr @~4000watts, run it through a bridge rectifier. I've seen guys on you tube attaching the rectifier to the heat sink of the scr. Not sure but sounds like you are saying this is a terrible idea. 2) get a dc driver. The problem here is that I can't find one with high hp @ 110vac. I can get ~3 hp @ 220vac & 180vdc, but the motors I'm looking at are 90-130vdc. Soooo not sure here.
    Lastly I could take a 36v power source and step it up to 90 but that's going to take more research for me.
    I'd love to hear your thoughts on the 3 alternatives.
    Thanks
    Raif



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