# Need some suggestion on high torque stepper motor

#### ahakou4321

Joined Nov 6, 2019
2
I'm interested in buying a high-torque stepper motor. Eventually the goal is to incorporate in a device that will be used to lift the lower part of a human leg below the knee. Based on estimating the weight of a human leg below the knee it should be able to hold a torque of at least around 3 N*m. So far the only motors that I could find within budget (< $50) is here with a corresponding driver here. 1) Does anyone have any experience with this vendor (oyostepper.com). Or can anyone give reasons to or not to purchase this stepper motor? Or is the budget too unreasonable for a decent quality stepper motor with this kind of holding torque? 2) Could anyone recommend what kind of battery would be needed to power this motor? #### BobTPH Joined Jun 5, 2013 3,334 How have you determined the torque needed? This depends entirely on the mechanical details. Motor torque can be increased by gearing and other means. Bob #### pmd34 Joined Feb 22, 2014 518 I would advise looking for a geared motor as to get high torque directly will mean the motor itself is rather heavy and so costly, but this may limit you on the speed. For a stepper motor something like this: https://www.aliexpress.com/item/32815520349.html?spm=a2g0s.12269583.0.0.6bcd1c923aqO9Y Is a good example (Planetary Reducer Stepper Motor) - though this one inparticular is probably a bit over geared and slow for your purpose. MANY people are using stepper motors for DIY CNC applications and 3D printers, so you can probably source them from China, ebay, aliexpress etc. rather than paying a reseller. You should however consider a simple DC geared motor, you would need some form of position feedback, with end switches or a simple rotary encoder (eg. Digital Potentiometer) to tell you where the motor was. The advantage of the DC motor is its much simpler to drive, and you can also sense the current it draws and determine if it have come up against an obstruction. (A stepper motor will just miss steps, and this can be a problem if you are using it beyond its torque range or speed.) A good DC motor option would be something like: https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20191205022731&SearchText=A58SW31ZY For powering these you can typically use 12 or 24V depend on what you buy. Actually for your application, have you considered using the mechanism from a car windscreen wiper? Thread Starter #### ahakou4321 Joined Nov 6, 2019 2 OK, I will check your link later, thanks very much #### GetDeviceInfo Joined Jun 7, 2009 1,850 OK, I will check your link later, thanks very much What would be the consequence of losing power and the leg falling? A smaller DC motor driving a worm reducer would give plenty of torque. A worm helix angle can provide a self holding function. #### MaxHeadRoom Joined Jul 18, 2013 23,166 #### MisterBill2 Joined Jan 23, 2018 8,808 I'm interested in buying a high-torque stepper motor. Eventually the goal is to incorporate in a device that will be used to lift the lower part of a human leg below the knee. Based on estimating the weight of a human leg below the knee it should be able to hold a torque of at least around 3 N*m. So far the only motors that I could find within budget (<$50) is here with a corresponding driver here.

1) Does anyone have any experience with this vendor (oyostepper.com). Or can anyone give reasons to or not to purchase this stepper motor? Or is the budget too unreasonable for a decent quality stepper motor with this kind of holding torque?
2) Could anyone recommend what kind of battery would be needed to power this motor?
In general stepper motors are very heavy for the torque that they deliver, and not only do they consume a lot of power, but they are a bit tricky to use and to drive. None of the medical devices use them , almost always there is a servo motor with gears and an encoder. And for an application like you described it will want a gear reduction drive since that will be far smaller and cheaper thana stepper motor, and also easier to control.