recumpence
1 GW
Hey Guys,
I have been working with a few guys lately regarding racing applications of various kinds. Also, there are a few threads running about racing setups and motor heat issues and I wanted to address that in a dedicated thread.
DISCLAIMER:
I am not a racer. I have rarely competed in any organized event. I am sure Luke and others will chime in with track experience. However, I want to layout the basics of racing setups and a few principals to get us off on the right foot.
We are all used to building commuter setups. Commuters differ from racing vehicles primarily in duty cycle as well as comfort. What I mean by that is;
Duty Cycle (this is also addressed as continuous versus peak power output). The duty cycle is the ratio of time a system can be hammered versus the time it must rest. For example, a refrigerator or a commuter car has a 100% duty cycle. It can run all the time. A circular saw may have a 20% duty cycle. So, for every 2 minutes it runs, the saw should sit for 8 minutes to cool. Now, for racing, we need to take the burst rating of a motor and somehow make that its continuous rating (turn the 20% duty cycle rating and trick it into a 100% duty cycle). (Oh, I am speaking about track racing here, not drag racing or hill climbing. Those can be accomplished with a high burst rating or low duty cycle rating alone). The primary issue for our bikes in racing applications is, obviously, cooling. Remember, for general riding, we run our motors with no additional cooling what-so-ever. That is fine for low output. But, for high output, active cooling is needed.
As for comfort, in racing, very little seat padding is needed, and we do not care about noise or a somewhat harsh throttle and brake setup (within reason), or looks, for that matter. What matters in racing is speed and durability, PERIOD!
To make our humble little motors to survive in a racing application (full throttle, full brakes, full throttle, full brakes, repeatedly) we need to remember a couple things;
#1 High RPM with low gearing is our friend. Low KV motors are fine to reduce heat and increase efficiency. But, for maximum power, you gotta spin it fast and gear it down. For example, my 4 turn 3220 was dynoed in delta and wye. The numbers are very telling. In wye the motor peaks at 95% efficiency. However, in Delta, it only peaks at 92% efficient. Yet, the Wye motor peaks its efficiency at only 2.3kw, whereas the Delta motor sees over 90% efficiency from 2.6kw all the way up to 9kw! The Delta motor has nearly 4ft lbs of torque at 9kw and 14k RPM. So, geared down for typical track riding, would net 50ft lbs at the rear wheel!
#2 Cooling. We need some sort of additional cooling. As for the Astro motors I am familiar with, heat sinks work well. However, it is good to pull even more heat from the motors. I am working on an integrated solution for that right now. Remember, for general riding, we hit the throttle once in a while and cruise the rest of the time. In racing, we are on the throttle, and off the throttle, then on, then off again. That is where the heat really builds up. Heat sinks with fans is the minimum needed to make a dent in cooling in racing conditions. Other solutions are even better. :wink:
#3 Overbuild it! For general commuting, we just need to make sure the bike can hold us and get us to our destination with charge to spare. In racing, you need to make sure the system can be beat to death and survive. That is a far different situation.
We are asking a lot out of our street systems. However, they CAN be made to survive. We just need to think outside the commuter box. What seems like stupid overkill on the street, may be barely adequate on the track. Even brakes are an issue (if we can get the motors to survive). I am working on a braking solution right now as well.
Racing is a matter of finding the absolute limit of a given component or group of components, then running that component or system right up to 99% of that number so it just barely survives the entire race. That requires testing or overbuilding to the point that you know there is a large margin to work with. However, that margin usually in expressed in added weight. That weight can slow you down.
At any rate, I am not a racer. But, these are some general guidlines to help out. I could post 10 times more information. But, for now, these are some things to chew on. I am sure others will chime in soon.
Maybe we need a racing section? Much of what I advise people on regarding their systems would be totally different if they were asking about a racing setup versus and commuter. Heck, I am building a racing trike for a customer right now that is going in a far different direction than any street commuter...........
Matt
I have been working with a few guys lately regarding racing applications of various kinds. Also, there are a few threads running about racing setups and motor heat issues and I wanted to address that in a dedicated thread.
DISCLAIMER:
I am not a racer. I have rarely competed in any organized event. I am sure Luke and others will chime in with track experience. However, I want to layout the basics of racing setups and a few principals to get us off on the right foot.
We are all used to building commuter setups. Commuters differ from racing vehicles primarily in duty cycle as well as comfort. What I mean by that is;
Duty Cycle (this is also addressed as continuous versus peak power output). The duty cycle is the ratio of time a system can be hammered versus the time it must rest. For example, a refrigerator or a commuter car has a 100% duty cycle. It can run all the time. A circular saw may have a 20% duty cycle. So, for every 2 minutes it runs, the saw should sit for 8 minutes to cool. Now, for racing, we need to take the burst rating of a motor and somehow make that its continuous rating (turn the 20% duty cycle rating and trick it into a 100% duty cycle). (Oh, I am speaking about track racing here, not drag racing or hill climbing. Those can be accomplished with a high burst rating or low duty cycle rating alone). The primary issue for our bikes in racing applications is, obviously, cooling. Remember, for general riding, we run our motors with no additional cooling what-so-ever. That is fine for low output. But, for high output, active cooling is needed.
As for comfort, in racing, very little seat padding is needed, and we do not care about noise or a somewhat harsh throttle and brake setup (within reason), or looks, for that matter. What matters in racing is speed and durability, PERIOD!
To make our humble little motors to survive in a racing application (full throttle, full brakes, full throttle, full brakes, repeatedly) we need to remember a couple things;
#1 High RPM with low gearing is our friend. Low KV motors are fine to reduce heat and increase efficiency. But, for maximum power, you gotta spin it fast and gear it down. For example, my 4 turn 3220 was dynoed in delta and wye. The numbers are very telling. In wye the motor peaks at 95% efficiency. However, in Delta, it only peaks at 92% efficient. Yet, the Wye motor peaks its efficiency at only 2.3kw, whereas the Delta motor sees over 90% efficiency from 2.6kw all the way up to 9kw! The Delta motor has nearly 4ft lbs of torque at 9kw and 14k RPM. So, geared down for typical track riding, would net 50ft lbs at the rear wheel!
#2 Cooling. We need some sort of additional cooling. As for the Astro motors I am familiar with, heat sinks work well. However, it is good to pull even more heat from the motors. I am working on an integrated solution for that right now. Remember, for general riding, we hit the throttle once in a while and cruise the rest of the time. In racing, we are on the throttle, and off the throttle, then on, then off again. That is where the heat really builds up. Heat sinks with fans is the minimum needed to make a dent in cooling in racing conditions. Other solutions are even better. :wink:
#3 Overbuild it! For general commuting, we just need to make sure the bike can hold us and get us to our destination with charge to spare. In racing, you need to make sure the system can be beat to death and survive. That is a far different situation.
We are asking a lot out of our street systems. However, they CAN be made to survive. We just need to think outside the commuter box. What seems like stupid overkill on the street, may be barely adequate on the track. Even brakes are an issue (if we can get the motors to survive). I am working on a braking solution right now as well.
Racing is a matter of finding the absolute limit of a given component or group of components, then running that component or system right up to 99% of that number so it just barely survives the entire race. That requires testing or overbuilding to the point that you know there is a large margin to work with. However, that margin usually in expressed in added weight. That weight can slow you down.
At any rate, I am not a racer. But, these are some general guidlines to help out. I could post 10 times more information. But, for now, these are some things to chew on. I am sure others will chime in soon.
Maybe we need a racing section? Much of what I advise people on regarding their systems would be totally different if they were asking about a racing setup versus and commuter. Heck, I am building a racing trike for a customer right now that is going in a far different direction than any street commuter...........
Matt