BS2 reading rc radio, measuring motor current/temp
iamscottym
Posts: 30
I'm currently working on a little RC car project. I have some hummer from radioshack that's becoming a project car. I fried the car's receiver by overdrawing the steering servo, so I will be replacing it with a futaba 2ph 2 channel. I've replaced the IC in the car's servo, since before the analog/pwm ic had been integrated with the receiver, with one from an off the shelf servo; works fine on my bs2.
However, I saw a thread here saying the bs2 couldnt catch the receiver's signal as fast as it was putting it out- it caught every other pulse. I know a few ms lag wont matter, but I have to do some other processing as well, so I'm a bit worried.
I'm also adding a sort of electronic transmission- basically, a motor is rated for power, within a general range of volts and amps(bldc dont really have the voltage limitation as brushed, but i'm using brushed here). Anyway, since a car's speed peaks at less than maximum power, I'll be adding more top-end by increasing the maximum voltage as a function of current. (basically, I'll create a table of currents/max voltages..with voltage up to absolute max(voltage of battery) pegged to a certain pwm #.
The unique feature I'm adding has to do with the battery wiring. Instead of hardwiring a pack, pairs of cells(liion 3.6V 1100mAh cells) will be hardwired in series; and then these pairs will be connected to eachother with pairs of relays. That way, I can switch between wiring them in series, and in parallel. At low voltages(0-7.2)..all cells will be in parallel- allowing for greater current draw, keeping the motor running at max power. However, when current drops, the cells will switch to series...so that the motor can get more voltage, less amps- same power as before. The greater voltage(to a point-dont wanna arch the comm) will allow higher speeds, without burning up the motor with too much power. The benefit of this, rather than just a big battery capable of doing the max current, and max volts hardwired- is weight/capacity. The car runs on a 7.2V 3.3Ah SC 6S1P nimh. However, I will be putting in 12 3.6V 1.1Ah liion cells(2S6P- relay switchable to 4S3P); which is already 33% more watt hours than the old pack- and the old pack is a huge upgrade over the 2Ah nicd pack it came with. I already get 20 minutes of run time- so I dont need more; a bigger pack would just slow me down, and potentially let the car run so long it'd overheat.
T do this, I need to measure current. By my estimates, I need to measure between 7 and 30A. I saw another thread recommending allegro hall effect analog current sensors- which is what I had initially been planning on using before I found the thread here. However, the only one that can go to 7A is a surface mount. Is there any easy way to mount this? Does anyone know of a digital sensor?- should I just use an A/D on the allegro? Is there another sensor that can measure from say, 3A-40A? I'd like a little more low end, if I could get it.
I will also need to be monitoring motor temp- with a temp sensor, just so I dont blow the motor- and I may end up cooling it if I think the transmission can handle it.
This is tons more processing for the BS2, so I'm worried about being able to read the receiver fast enough. If I need something faster, reccommendations would be great. I've been looking at a rabbitcore 3750..since i could use it for datalogging and another project I'm working on, and its not that expensive compared to a faster stamp..though doesnt have the support you guys offer.
Any input would be appreciated, thanks.
Scott
However, I saw a thread here saying the bs2 couldnt catch the receiver's signal as fast as it was putting it out- it caught every other pulse. I know a few ms lag wont matter, but I have to do some other processing as well, so I'm a bit worried.
I'm also adding a sort of electronic transmission- basically, a motor is rated for power, within a general range of volts and amps(bldc dont really have the voltage limitation as brushed, but i'm using brushed here). Anyway, since a car's speed peaks at less than maximum power, I'll be adding more top-end by increasing the maximum voltage as a function of current. (basically, I'll create a table of currents/max voltages..with voltage up to absolute max(voltage of battery) pegged to a certain pwm #.
The unique feature I'm adding has to do with the battery wiring. Instead of hardwiring a pack, pairs of cells(liion 3.6V 1100mAh cells) will be hardwired in series; and then these pairs will be connected to eachother with pairs of relays. That way, I can switch between wiring them in series, and in parallel. At low voltages(0-7.2)..all cells will be in parallel- allowing for greater current draw, keeping the motor running at max power. However, when current drops, the cells will switch to series...so that the motor can get more voltage, less amps- same power as before. The greater voltage(to a point-dont wanna arch the comm) will allow higher speeds, without burning up the motor with too much power. The benefit of this, rather than just a big battery capable of doing the max current, and max volts hardwired- is weight/capacity. The car runs on a 7.2V 3.3Ah SC 6S1P nimh. However, I will be putting in 12 3.6V 1.1Ah liion cells(2S6P- relay switchable to 4S3P); which is already 33% more watt hours than the old pack- and the old pack is a huge upgrade over the 2Ah nicd pack it came with. I already get 20 minutes of run time- so I dont need more; a bigger pack would just slow me down, and potentially let the car run so long it'd overheat.
T do this, I need to measure current. By my estimates, I need to measure between 7 and 30A. I saw another thread recommending allegro hall effect analog current sensors- which is what I had initially been planning on using before I found the thread here. However, the only one that can go to 7A is a surface mount. Is there any easy way to mount this? Does anyone know of a digital sensor?- should I just use an A/D on the allegro? Is there another sensor that can measure from say, 3A-40A? I'd like a little more low end, if I could get it.
I will also need to be monitoring motor temp- with a temp sensor, just so I dont blow the motor- and I may end up cooling it if I think the transmission can handle it.
This is tons more processing for the BS2, so I'm worried about being able to read the receiver fast enough. If I need something faster, reccommendations would be great. I've been looking at a rabbitcore 3750..since i could use it for datalogging and another project I'm working on, and its not that expensive compared to a faster stamp..though doesnt have the support you guys offer.
Any input would be appreciated, thanks.
Scott
Comments
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think outside the BOX!
I know I can do this with hardware, but with software its easier to change.·