Traction
A common problem with OpenMower mowers (particularly the YardForce 500) is a lack of traction. This can cause the wheels to slip, especially when turning, and can cause the mower to become stuck. The YardForce 500 is underweight for its wheels, and the issue can be exacerbated if the yard is sloped, bumpy, or soft. There are a number of modifications people have experimented with to try to improve the traction.
Adding Weight
This is the most highly recommended approach on the YardForce 500. Moving the center of mass back towards the driving wheels is the primary goal.
Adding weight inside the wheels
The Yardforce 500 wheels are hollow, and you can place extra weight inside the wheels. Although this will not move the center of mass as much as placing the weight behind the wheels, it has the advantage of not stressing the bearings/bushings with the extra weight.
@kombo-kevinmce created a 3D printed design for compartments inside the wheels to contain lead balls or other weights. Each wheel fits about 1200g: https://discord.com/channels/958476543846412329/961803746399101008/1236423223705600120 https://www.printables.com/model/533638-yardforce-classic-500-wheel-weight
@Prigor used wheel balancing weights packed inside the wheels to add 1560g to each wheel: https://discord.com/channels/958476543846412329/961803746399101008/1236716061928198334
@CSobel added lead balls embedded in epoxy to the wheels: https://discord.com/channels/958476543846412329/961803746399101008/1106556852491255838
@Vermut added steel flakes embedded in silicon sealant: https://discord.com/channels/958476543846412329/961803746399101008/1224050218983751741
@Ow added lead sheets to the wheels: https://discord.com/channels/958476543846412329/961804411112394842/1118625329309814784
Adding weight behind the wheels
@bussel - (bodop) suggested a mod that worked on other mowers, hanging weights off the back with sticks: https://discord.com/channels/958476543846412329/961803746399101008/1151412390924132362
@tr8 created a printable design for mounting weight behind the wheels, but it is not necessarily YardForce 500 compatible: https://www.printables.com/model/703384-balance-weight-for-yardforce-robotic-mower
Wheel Spikes
Some people have also had success with mounting longer spikes on their wheels to get better traction. Note that if you add spikes, it will likely change the wheel radius and so you will need to update the wheel ticks parameter in order to not have jerky motion.
Metal Spikes
There are two brands of commercially available aluminum spikes, Mibrobo, and Robo-Claws
Mibrobo
Mibrobo spikes are more expensive but are coated and may have a better spike design (?)
No OpenMower users have reported their experience with them.
Robo Claws
Robo-Claws spikes are cheaper and have an installation guide as part of the official docs: https://openmower.de/docs/contributions/mount-wheel-spikes/
@Vermut reports "can't say they are super-effective for me. Hence the extra weight attempt" https://discord.com/channels/958476543846412329/961803746399101008/1224255287284858900
@Prigor reports "I had metal spikes for a long time and they were good on grass but got rounded after one year of use and started slipping. And they were terrible on anything concrete or hard" https://discord.com/channels/958476543846412329/961803746399101008/1253295856413577318
Self-Printed
Other users have suggested making your own spikes following a similar design on a CNC or laser cutter. There aren't any reports of users doing this.
Plastic Spikes
@kombo-kevinmce Created designs for a few different 3D printed plastic spikes: https://www.printables.com/model/567409-yardforce-classic-500-wheel-spikes
17mm spikes
@kombo-kevinmce reports "The 17 mm spikes are probably too long and for me they cause the mower to wobble as the spikes are lifting the mower. "
@Prigor reports "I also tried these printed spikes from @kombo-kevinmce but I found them to be too bumpy." https://discord.com/channels/958476543846412329/961803746399101008/1253295856413577318
dual spikes
@kombo-kevinmce reports "They worked about the same as the larger id say" https://discord.com/channels/958476543846412329/961803746399101008/1253228544234885221
full ring spikes
@Dahefe reports "I printed a set of wheel spikes (full rings - https://www.printables.com/model/567409-yardforce-classic-500-wheel-spikes/files) in ABS and they work great! I also changed my NAV areas that are on concrete to make them narrow which make the planner slow down (I think). I can see the spikes wearing down and plan on replacing the rings once a year." https://discord.com/channels/958476543846412329/961803746399101008/1253311235324383272