Hi all, I am a complete noob to all this but I’m pretty good at following directions and can read schematics for the most part. I am trying to build a dynamic balancer to balance small engine crankshafts. I was thinking of using a stepper motor and 2 20Kg load sensors with a cradle mounted on each one the crank would set on. The stepper motor would be used to spin the crank to 300-500 RPMs and as the crank is out of balance, would cause a force to be applied on the load sensor. A few things I am trying to achieve with this project is as follows.
Display force applied to load sensors on individual digital displays, one for each load cell and have it read highest load.
Using the stepper motor as an encoder with a processor of some sort to record the position the highest load was detected during rotation and have it display the position via an LED bar graph display, again one for each side.
Have the previous recorded information reset when the motor is powered back on to spin the crankshaft.
As I said before, I have no idea how to do this but sure someone here knows how. The closest thing I could compare this to would be a tire balancer, easily googled with good pics of the display in case anyone needs a visual to understand what I was trying to explain LOL.
If I could work with anyone here to get a parts list and a schematic, that would be so awesome. Hopefully I don’t sound lazy, I wish I could learn this stuff but this is one subject ive never been able to grasp, but maybe some folks on this forum could help me out. If I can answer any questions or go into more detail, please ask. I would really love to do this project and see it work.
I do some work with scales and other force measurement instruments and the idea is easy enough to visualize with the trouble being in the construction. Two load cells, each with a little freedom to deflect in both directions, mounted at 90° to each other at the shaft’s end might give you some interesting data. They do have dual axis (&more) load cells as well but the costs get very high.
I’d build in provisions for slow, controlled rotating with arbitrary holding, too. I think a slow turn in a horiz orientation will better show where in the rotation/which shaft component the unbal condition occurs. In other words, when troubleshooting shafts, you want the data bumpy, not circular.
Hi brow, thanks for the reply. I am basing the design from some newer style balancers that I’ve researched. Here is a drawing to illustrate what I’m talking about.
This is a side, frontal view of the balancer stand and the control/display panel.
So here is the procedure walk through. The bobweight is made up to mimic rotating mass of rod and a percentage of the reciprocating weight of the rod and piston (typically 50-62%). The crankshaft is placed on the rollers and Nema motor is connected via flexshaft. The start button is pressed and the balancer will first perform a tare function and reset to zero, once the scale is reading 0 the motor will ramp up to 500 Rpms, once the motor has settled at 500 rpms, the balancer will spin for 15 seconds to gather the peak force on each load sensor and read the encoder to store at what position of rotation the peak occurred. The motor will the slow to a stop and the peak weight recorded will be displayed on the numeric display. By turning the crank by hand, the degree of rotation the peak weight will be displayed on the location indicator bar graph. When the bar is illuminated between the two arrows, this will indicate the peak was captured at the 180 degree mark ( I will install a laser to pinpoint the exact 180 degree location). The crank is removed, drilled to remove the displayed weight from each side and placed back on the balancer. The start button is pressed and the whole procedure is repeated. I want to program a weight threshold say 2 grams, so same procedure but after running for 15 seconds if the balancer doesn’t sense more than 2 grams, the second rpm range indicator will illuminate and the balancer will spin up to 1000 rpms and hold for 15 seconds. Same as before, the weight and location will be displayed. Wash, rinse, repeat.
So with a given the illustration and description of what I want to accomplish, will the load sensors, motor and microcontroller work for my project? If so I can go ahead and order the above listed parts. Pretty sure the motor and load sensor will be okay but, is the microcontroller a good choice for this job?
The biggest hurdle to this project is the coding, I have no idea where to start. As a machinist the construction is simple but ignorant to the electrical part. Hoping to find someone here that may be able to write the code for a copy and paste. Any help is greatly appreciated, thanks so much.
I’m way out of my lane here but I don’t understand why you need to spin it fast or look for peaks. Can’t you take your force measurements at 20° intervals during one slow rotation? When the load on each load cell (read them independently) doesn’t change during rotation, it’s balanced. I guess you could spin it fast then.
Edit: Anyway, I’ll take your word for it. For controls, consider a commercial force instrument. This one below has a ton of what you’re hoping for already built in, especially, dual chan, peak hold, fast sampling (3kHz):
