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Calculation of the collators reward for Robonomics Parachain in Polkadot #510

@dergudzon

Description

@dergudzon

Robonomics collators are an integral part of the infrastructure, maintaininig Robonomics app (parachain) by collecting IoT devices transactions and producing state transition proofs for Polkadot's validators.

To keep collator's owners motivation to stay in the network, the reward per block must be periodically adjusted based on the following factors:

  • The reward must not only cover the cost of the reference hardware running the Robonomics node, but also yield up to 30% profit.

  • The reward size must take into account the minimum desired number of active collators in the network.

  • The calculation must use either the current XRT price or the minimum desired XRT price.

Accordingly, when any of the above‑described parameters changes significantly, the reward must be recalculated.

Initial data

As reference hardware, we can take a dedicated server at OVH (AMD Epyc 4345P 3.8 GHz + 64 GB RAM + 2×960 GB NVMe). Currently, the collator’s full database occupies 1.1 TB; therefore, with the disks combined into a raid0 array, there will be about 800 GB of free space on the server.

  • The cost of such a server is ~$170 per month, or ~$2,040 per year.

  • The minimum desired number of collators at present is 7.

  • The XRT price is $1.

  • The actual average block time in Robonomics Polkadot over the last two weeks is approximately 7 seconds, so the number of blocks per year is
    (60 × 60 × 24 × 365) / 7 ≈ 4,505,143 blocks.

Reward calculation

Reward per block = (server_cost_per_year × number_of_collators + 30%) / number_of_blocks_per_year / XRT_price

Substituting the values:
(2040 × 7 + 30%) / 4505143 / 1 = 0.004120624

Rounding up yields 0.0042 XRT per block.

Conclusion

Taking into account current hardware prices and the XRT price to support the minimum required number of collators in the network I propose setting the reward at 0.0042 XRT per block.

As network usage grows and the token price rises, the pool of validators who would benefit from supporting Robonomics as a collator will organically grow.

The team currently aims to create conditions for collators that would incentivize a small number of providers to support the network.

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