Saturday, 10 March 2018

Lets talk about Stepper Motors - Episode 207

Stepper Motor kits abound on Ebay and unfortunately all too often they are not very good kits.
They sound great. Huge holding torques, very very reasonably priced drivers, motors and power supplies. Unfortunately most of these kits use poorly designed stepper drivers, they are feed with low voltage power supplies and the motors are a very poor match for the drivers that have the job of making them turn.
 
In this video I try and show the issues associated with stepper motors, why they are as they are and how to choose a well matched system. The drive system on your machine is the biggest hardware investment you will make and one of the most important. It doesn't matter how good the machine is, if your drives are rubbish so is your machine.

 Click to watch video



The biggest myth of stepper motors is that bigger is better.
While in some respects this is true, there are certain criteria that must be met. The motor, driver and power supply must compliment one another to get the best out of your motors. A small well matched system will invariably out perform a poorly matched motor / driver / power supply combination.
Stepper motors are rated in holding torque which is how much power they have when they are doing nothing. The larger they are the better they will do nothing for you.
Big stepper motors are sold to catch the buyer not run your machine. The bigger the motor the bigger it's internal losses are and the more power you require overcome these losses and drive them properly. Don't get me wrong. There is nothing wrong with a properly driven stepper motor and in many cases large motors are needed to move heavy axis. Generally though the home builder making their DIY machine does not need to exceed 400 ozin or so unless it is a big heavy machine they are building or they need it to move very fast. Medium powered motors are more common in this hobby.
The problem comes when kits sold on the likes of ebay driven by a TB6560 based driver board using a 24 volt power supply and trying to drive 425 ozin motors. The TB6560 boards were never very good to start with and many of the boards have design flaws that have been extensively discussed on the CNC Zone over the years. The voltage is way too low to drive a medium size stepper motor and many of the adverts don't even give you the basic specs of the motors.
It is vitally important to check the spec on every part of any kit being offered and make sure it is a reasonable match for the rest of the system. If it isn't or there are no specs then move on and find something else.

Additional Information

Click the link below to download the Spreadsheet for calculating Drive voltage and current requirements.
http://bit.ly/2I3SLSW

Click the link below to visit the Gecko site and read their Stepper motor guide. 
http://www.geckodrive.com/support.html

Click below to download the Stepper motor guide.
Stepper Motor Basics.pdf

My personal opinion
One thing in Geckos stepper motor guide that I disagree with is the sizing of the motors. While I am sure they are correct in their assessment, they are talking about a product you may be producing that will never change. As a hobbyist we are constantly tinkering and upgrading. In the case of purchasing a Gecko G540 I would purchase the largest motor that it could correctly run rather than one that fits my needs today. In the case of the G540 that is the 381 ozin motor I showcased in the video which if memory serves my correctly was actually specially made to compliment the G540 drive when it first came out. No matter how big a motor you put on it you will not get any more power out of it. A larger motor will give you more power at slow speed but as you try and move faster it will rapidly loose power and the 381 ozin motor will out perform it. Not only that but that little motor is capable of running a range of Joe's DIY CNC machines built up to 4 x 8 foot configuration for example. 
They will drive your small machine today and can be moved to a larger one tomorrow.

It is also important to note that Gecko are not the only makers of good drives systems on the market but the G540 is the only one that I have experience with which is why I reference this one.

4 Axis Drive kit.
I wish to point out that by using the links below I will earn a commission on any purchase you make at no additional cost to you. It is important to note that if you purchase the individual components making up the kits from various suppliers and assembly them yourself you will save yourself money. Your responsibility is to yourself and I will be happy no matter where you purchase your drive solution from so long as they work well for you. I encourage you to look around for the best deal and solution that meets your needs. I have not personally purchased from this supplier but it is a USA based company that is selling this product.

It is important to note that this supplier does have a 3 axis kit but I would recommend asking them to price you this kit and leaving off the extra motor and 12 foot cable if you want 3 axis. Their current 3 axis kit uses a 7.3 amp power supply and if you want to add the 4th motor later you will need to upgrade the power supply to power it. Getting the 12.5 amp supply now will save later on. It never hurts to have a spare motor and cable just in case, if funds allow. Buying a 4 axis motor kit for your 3 motor machine is not crazy. When you want to add a rotary axis or have a faulty motor or cable you will have the parts you need..


With this kit you will need to supply a case or build one to house it in and a minimum of wiring is needed. If you want an Estop button you will need to purchase this separately.
The Gecko G540 has a built in Break out board to which you can add relays and limit switches. Additional wiresare added to the G540 using screw terminals so those who are not comfortable soldering need not worry.

This kit includes:
4 x 381 ozin motors
4 x 12 foot cables to the motors
1 x 6 foot parallel cable  
1 x 48 Volt 12.5 amp power supply
1 x Gecko G540 4 axis drive system



http://ebay.to/2HiENeA
Please let me know if this link stops working or the kit no longer matches the photo above.
Use the contact link on the right.

Mushroom emergency stop switch if you want one.
http://ebay.to/2oYF281



Support my Channel
If you would like to support my channel you can do so by using the link below whenever you make a purchase from ebay. By using it I will receive a small commission at no additional cost to you which will go toward making new videos. The link below will take you to the bay home page where you can do your shopping as you normally do. 
Thank you for your support.

http://ebay.to/2HllO3g


http://ebay.to/2HllO3g






No comments:

Post a Comment