What drivetrain combination do you guys use and what do you think is more efficient/better at games where speed is important but you get a lot of defense (Destination deep space).
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There are really three questions here.
- What gear ratio should I use?
- How much power do I need?
- What kind of motor should I use?
Answering each of these in order:
1. The tradeoff here is between top speed and top acceleration. There are a number of factors that come into play here. Ideally, you want to pick a gear ratio that gives you the quickest time to travel your most commonly-traveled distance, while also giving you enough power to not self-destruct when defended. I suggest using ILITE’s Drivetrain Simulator to help with this decision.
2. How much power you need is really function of how fast you need to travel and how hard you need to push. There’s no right answer to which combination of motors is best; it will depend on the game you’re playing and the strategy you’re using to play that game. Again, you can use ILITE’s calculator to help you decide if you can get away with fewer motors without sacrificing the speed, pushing power, or per-motor current you need.
3. Here is where the choice really comes in. 2 CIMs, 3 Mini CIMs, and 2 NEOs all have about the same power and free speed. But like everything, each motor has its positives and negatives, and it’s you’re job as an engineer to choose which is best for your application. So why choose one over the other.
You might choose Mini CIMs over CIMs because in total they have a higher thermal mass, so they heat up slower over time. That means that even though they start at the same power, 3x Mini CIMs have ~25% more power than 2x CIMs after 120 seconds at full power. You can see this by comparing the two Peak Power Tests at motors.vex.com. On the other hand, using Mini CIMs requires two extra PDP slots and weighs ~1.5 lbs more than CIMs.
You may choose NEOs over CIMs because of their higher efficiency and better faster cooling. NEOs are brushless motors, meaning that the motor coils are attached to the motor body (stator) instead of the shaft (rotor). Since the coils that heat up are now directly attached to the casing, heat can be transferred and dissipated from the casing. Compare this to brushed motors, where heat has to travel through either the air inside the motor or the internal motor bearings in order to escape. All in all, this makes the motor more efficient and lets it run for longer periods without cooling breaks. NEOs are also substantially lighter than CIMs. You may not want to use NEOs because they require using SPARK MAXs, which are missing some features you can get with brushed motors using the Talon SRX.
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I believe that there is a more significant change from 2 to 3 miniCIMs per side compared to changing from 2 to 3 NEOs per side.
You can take a look at this spreadsheet.
You will see our design criteria for 2019, and expected performance for 2019. We used 3 NEOs per side in 2019.
You can also see our design - and I believe design criteria for 2018. We used 3 miniCIMs per side in 2018.
Our experience was also that the NEO operate significantly cooler than miniCIMs.
If you want to investigate different criteria, update those fields.
If you want to investigate different gear ratios, likewise.
Have fun!
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This season we started with 2 cims but for IRI and the rest of our offseason we have 3 neos. I honestly think they are very similar in drivability but I would pick neos any day because they are lighter and more powerful. At worlds we played very lackluster defense for our alliance but at IRI we played much stronger defense I think because of that extra power we have from the neos
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