Are people thinking about rc performance all wrong today?
Posted: Thu Aug 18, 2011 10:21 am
I had a bit of a brainstorm with my friend Chad yesterday. We both started racing when many of you did back in the mid 80's. Back then due to a lack of battery power and motor efficiency we'd strip the cars down as light as we could get them in the hopes of being as fast as possible with the available power. Today power and run time are not an issue. Motors are more powerful than ever and many of the brushless motors have tons of low end torque compared to the brushed motors. We are also seeing people add weight to their cars for better handling. It sounds weird but I've seen it work. Is this mentality backwards? It seems counter to what we always did. Even in the real world of racing, cars are as light as possible. The real question of course is how light is too light?
Chad and I have always been Mazda RX-7 guys. Historically Japanese cars have typically been lighter in weight than their American car counterparts. They have also been lower in power. Their engines are smaller with less low end power but more rpm. It has always balanced out fairly well. You'd have the Japanese sports cars that were light and nimble with their small motors and less overall power and then you the American cars which were heavier with larger engines that had more power but at a lower rpm. Both designs had their advantages and disadvantages and were good in different ways. Times are changing of course and this doesn't necessarily apply anymore but then we got to thinking about the same idea in rc.
It seems like modern rc is turning more into the old American car template. It's more powerful but heavier. People are adding weight in the name of handling. The 2 heaviest things in our rc cars are the motor and the battery. The rest of the electronics have gotten to be very small and very light. Battery life is also so great today that you can typically run for a couple of qualifying runs on the same pack and keep in mind these heats are typically longer than what we used to run back in the day. What I'm getting at is we have more battery life than we need to race. A race car carries enough fuel to get the job done and no more. Why not in rc?
So you may have some idea of where I'm going with this so I'll finally get to it. Why not get the cars back down to as light as possible? I don't mean as light as the rules allow I mean as light as POSSIBLE! Keep in mind that a lighter car takes less abuse in a wreck than a heavier car does. It's physics. We can only get the chassis down so light though so the savings need to come in other ways. Now lets say we power our light cars with 1 cell lipos. Half the size and weight of a 2 cell depending on your mah rating. I know you're thinking that we've just slowed down to a crawl due to half the voltage but here's where the Japanese car mentality takes over. Run a very low turn motor like a 3.4T or 4.5T brushless. You won't have any low end power of course so will require higher rpms. As an example if we have a 3300kv motor on 7.4V, you get 24,420 rpm. Theoretically. Now if we ran half the voltage at 3.7v but on a hotter motor such as a 6600kv motor, we'd still theoretically get 24,420 rpm but with a narrower usable power band of course. The reality is that we'd want a hotter motor than this still. If you think this won't work then take a look at 1/12 scale on road. Yes those cars are lighter and on smoother tracks but the point is to get our off road cars down as light as possible. Modern tracks are pretty high grip and slipper clutches can be adjusted. Sure you are still going to have less power available but then again it would need to push around less total weight. It doesn't need to be the fastest on the track. It just needs to be competitive. The idea being that the lighter weight will equal a more nimble car with the hopes that the chassis would make up the rest of the time.
I'm not saying this is a valid idea but it is an idea that I feel could potentially work. We won't get 30 minute run times anymore but if they could get 8-10 minutes then it should be enough to get the job done. The cars would be lighter which would make them more tolerant of wrecks and with less weight the suspensions could be setup softer which would make it quite nimble over rough sections of track.
Maybe it's a stupid idea. Then again, maybe it could work. I'm curious nevertheless. Discuss...
Chad and I have always been Mazda RX-7 guys. Historically Japanese cars have typically been lighter in weight than their American car counterparts. They have also been lower in power. Their engines are smaller with less low end power but more rpm. It has always balanced out fairly well. You'd have the Japanese sports cars that were light and nimble with their small motors and less overall power and then you the American cars which were heavier with larger engines that had more power but at a lower rpm. Both designs had their advantages and disadvantages and were good in different ways. Times are changing of course and this doesn't necessarily apply anymore but then we got to thinking about the same idea in rc.
It seems like modern rc is turning more into the old American car template. It's more powerful but heavier. People are adding weight in the name of handling. The 2 heaviest things in our rc cars are the motor and the battery. The rest of the electronics have gotten to be very small and very light. Battery life is also so great today that you can typically run for a couple of qualifying runs on the same pack and keep in mind these heats are typically longer than what we used to run back in the day. What I'm getting at is we have more battery life than we need to race. A race car carries enough fuel to get the job done and no more. Why not in rc?
So you may have some idea of where I'm going with this so I'll finally get to it. Why not get the cars back down to as light as possible? I don't mean as light as the rules allow I mean as light as POSSIBLE! Keep in mind that a lighter car takes less abuse in a wreck than a heavier car does. It's physics. We can only get the chassis down so light though so the savings need to come in other ways. Now lets say we power our light cars with 1 cell lipos. Half the size and weight of a 2 cell depending on your mah rating. I know you're thinking that we've just slowed down to a crawl due to half the voltage but here's where the Japanese car mentality takes over. Run a very low turn motor like a 3.4T or 4.5T brushless. You won't have any low end power of course so will require higher rpms. As an example if we have a 3300kv motor on 7.4V, you get 24,420 rpm. Theoretically. Now if we ran half the voltage at 3.7v but on a hotter motor such as a 6600kv motor, we'd still theoretically get 24,420 rpm but with a narrower usable power band of course. The reality is that we'd want a hotter motor than this still. If you think this won't work then take a look at 1/12 scale on road. Yes those cars are lighter and on smoother tracks but the point is to get our off road cars down as light as possible. Modern tracks are pretty high grip and slipper clutches can be adjusted. Sure you are still going to have less power available but then again it would need to push around less total weight. It doesn't need to be the fastest on the track. It just needs to be competitive. The idea being that the lighter weight will equal a more nimble car with the hopes that the chassis would make up the rest of the time.
I'm not saying this is a valid idea but it is an idea that I feel could potentially work. We won't get 30 minute run times anymore but if they could get 8-10 minutes then it should be enough to get the job done. The cars would be lighter which would make them more tolerant of wrecks and with less weight the suspensions could be setup softer which would make it quite nimble over rough sections of track.
Maybe it's a stupid idea. Then again, maybe it could work. I'm curious nevertheless. Discuss...