Hello Rory,
I know it recommends the polycarbonate V-Wheels but I would like to know if we can use the Delrin wheels without any issues? What was the reason you chose the polycarbonate for this specific project? If there is any glaring problems you can see with using the delrin wheels please let us know.
Thank you.
Delrin is superior in all aspects except UV resistance. It is possible though difficult to find delrin in UV resistant grades. If using delrin outdoors, I would recommend shading the wheels from the sun.
I should also note that delrin has a lower heat deflection temperature than some grades of polycarbonate, and about the same as others, but it should be high enough for this application, particularly if the wheels are shaded from the sun.
What a great answer. Thank you for replying.
Any idea how long a wheel would last? 1 day/month/year?
(assuming sunlight everyday)
It is really hard to say how long the wheels might last. White is much more susceptible than black. If I were to guess, if using standard black delrin, I would say you might get a year maybe a bit more from them. If you want to machine your own, I would recommend this UV resistant grade of delrin: http://www.professionalplastics.com/Delrin_527
Thank you for the great info 
Great question Shaun, and thank you for your helpful responses @jenkitay!
We used to use the delrin wheels and they worked just fine. I think we had ours outside for at least a year without any problems. Once the polycarbonate wheels were available, we switched over. In addition to better UV resistance, we decided to go with the polycarbonate wheels because they are harder. This is important for the wheels on the cross-slide because a fully-extended z-axis acts as a giant moment-arm, placing a lot of force on the cross-slide wheels. The delrin wheels compress more than the polycarbonate ones which causes increased wobble at the end of the fully extended z-axis.
@roryaronson good point. hardness would indeed matter, and it will vary depending on the grade, for either delrin or polycarbonate.
Hi @roryaronson ,
I have a small addition to this question, it seems like the consensus on the v wheels is poly carb is better, but when I googled it, I got on a forum and got linked to these two websites:
http://www.sawmillcreek.org/showthread.php?139045-Plastic-Comparisons-of-Delrin-Acrylic-and-Lexan
and:
http://www.machinist-materials.com/comparison_table_for_plastics.htm
It seems like these two both show Delrin as the better material for, hardness, compression, etc. Did the poly carb wheels make a noticeable difference or where they just switched out because OpenBuilds advertised them as “better” (I am only asking because of the insane markup that OpenBuilds has on its very inexpensive parts, so I feel like they are just trying everything they can to make money and I think they may tailor the info on their website to follow suit. Though the poly carb totally could be better and it wouldn’t surprise me.)
Great research David! The main issue I see in determining which is a better material is that there are many types of Delrin, each with their own properties. So its going to be dependent on which specific Delrin is used because the range of yield strengths is actually quite large: 26 to 74Mpa according to Wolfram Alpha.
The Delrin that OpenBuilds is claiming to use has a yield strength of 63Mpa, while the polycarbonate they say has a yield strength of 86Mpa. Wolfram Alpha claims PC to be 83Mpa but I’m sure it also depends on the specific polycarbonate and the testing equipment and conditions used. Either way, the OpenBuilds PC is claiming to be ~30% stronger.
While we have not tested the two materials from OpenBuilds ourselves, when we made the switch to PC wheels we did notice an increase in rigidity in the system. However, like I said before, we originally used the Delrin wheels without any issues. Furthermore, since we switched material type, we have added more wheels to the design to further increase the rigidity despite the wheel material.
At the end of the day, you’re probably fine using Delrin if you’d like to save some money. Though we’ll be producing all of our kits with polycarbonate, and will also be opening up our own parts shop once all the kits are out the door.
I’ve been building combat robots (aka, battlebots, robot fighting league) since the mid 1990’s. I’ve been building robots for of other types for almost 40 years.
Delrin is much better than Polycarb for wheels. Polycarb will absorb chemicals. It shatters and chips on lateral (which in this case would be radial) impacts.
Delrin is quite a bit more expensive. UHMW is a good compromise material. Both UHMW and Delrin are quite “slick”, like teflon so they don’t provide much traction. I typically use glass fiber filled Delrin for outdoor (all weather/temp) parts. A 6"x6"x1" block of the stuff is more than a hundred dollars.
For my robots, I typically make billet Aluminum wheels (6061-T6) and then cast a thin layer of rubber on the outside if I want traction or just run them as disks if I’m just using them for locomotion/rollers. I’d go with 6061 over any plastic for a non-traction wheel.
On a similar note, oil impregnated bronze bushings are much better than the roller bears for low velocity wheels. They are way cheaper, don’t break have a very wide temp range, require no maintenance and don’t break. Long story short, an aluminum wheel with a bronze bushing would be a great wheel configuration.