Coin sorting ramp
One of the components needed to automate coin intake is the coin sorting ramp.
The purpose of this ramp is to allow inserted coins to be automatically sorted into the right place so they can be dispensed at a later time.
After a few quick searches, I found various designs that fit our needs. You can find the rest of the designs and variations in the References and Inspirations section
Coin Sorting ramp
Fast prototype print - low quality
The first step is to create a rough prototype that can ensure that this piece works as expected and that it’s fit for purpose.
The first prints came out a bit worse than expected in terms of surface finish.
This surface finished really impacted the accuracy of the coin selection.
This is something I had not seen in other types of prints (I have always printed in low quality = thick layer height, to reduce printing time and maximize speed)
This is a coin cylinder, also printed in low quality. Notice how the top layer was superb and without hiccups or jumps!
I was expecting the same finish.
Slow print - high quality
After changing the quality of the print and the layer height in Cura, and retrying a second print (2x slower than the first one), the quality of the top surface did not improve significantly.
Prototype outcomes:
- The sole sizes work well for Euro coins (Excellent!)
- The surface finish is terrible and impacts sliding and friction coefficients (Could be fixed, if needed)
- The overall piece size is too small for our needs (Fixable by using a different manufacturing method)
Conclusion: I will use the hole sizes from the existing design, but I will have to laser cut it to create a piece that is long enough for my needs.
Coin ramps and coefficient of static friction
Empirical evidence and trials with smooth acrylic surfaces have demonstrated acceptable sliding speeds (and no slowdowns) on ramps that have > 21.2’ degrees off of the horizontal axis.
Using an existing piece of acrylic, I calculated the min. height it should be raised to guarantee that none of the coins will get stuck (slowed down to a halt) to it.
That magical number was 90mm on the upper side of a 250mm surface.
A quick calculation gives us the needed result for our designs.
Making my maths teachers proud
Congratulations… you finally got me.
I guess remembering all that Trig. trivia finally paid off, eh? You win… I hereby admit publicly that it might be useful (somehow).
2D design
This also means that we need to adjust the distances for the elements on the ramp at 22 degrees:
If the separation of the coin cylinders will be 55 mm, the holes on the ramp have to be ~60 mm apart.
A fairly noticeable difference!
The finished component
Coin ejection ramp
The coin ejection ramp uses the same design, except it does not have any holes in it.
Assets
Assets: Assets in gitlab