Measurements and Benchmarks
Top Speed
To get the maximum speed I setup to tape lines 3m apart and filmed the car while I made several passes. The camera records at 30fps, so I have +/- 3.3% error from the camera and maybe +/- 1% error from the tape lines.
To get the maximum speed I setup to tape lines 3m apart and filmed the car while I made several passes. The camera records at 30fps, so I have +/- 3.3% error from the camera and maybe +/- 1% error from the tape lines.
The car could travel 3m in 0.7 seconds (21 out of 30 frames in 1 second).
Top Speed: 4.3m/s = 15.5km/h = 9.6miles/h
DistanceI took the router in to a big field. I could connect with my laptop up to 500m away (at 1Mb). After that distance, I could no longer connect. The alternative firmware (OpenWRT) allows you to increase the output power. I tried modifying this value, but it made no difference at all to the distance I was able to connect to it. Perhaps my laptop (Dell Inspiron 6000) which has always had good wifi connectivity (better than my friend's 6400), may be the limiting factor.
Data Rates
Control Signals: 3.5KB/s
Camera: 50-190KB/sThe camera used more/less bandwidth depending on how much light was in the image. If there was lots of light, it would use more bandwidth.
Control Signals: 3.5KB/s
Camera: 50-190KB/sThe camera used more/less bandwidth depending on how much light was in the image. If there was lots of light, it would use more bandwidth.
If the car was to be driven from very far away, the router would continually negotiate a lower speed until it reached 1Mb (megabit). At this speed, the camera wouldn't be able to send back data, but the control signals would still be working.
Power Measurements
Power Measurements
I noticed whenever the current changed during car bootup and noted the time. The measurements were done on the battery side before the voltage was dropped down to whatever voltage the device needed. Measurements were taken when the batteries had been used for about 10 minutes and V=15.3V. Since the current was measured here, the current going in to the device at a lower voltage would be higher. All measurements were completed with a Fluke 187 True RMS Multimeter. The last measurement noted was when the device reached a steady-state.
Camera
Time (seconds) | Current (mA @ 15.3V) | Current (mA @ 9.2V) | Power (W) |
0 | 39 | 65 | 0.6 |
5 | 58 | 96 | 0.9 |
8 | 98 | 163 | 1.5 |
Router
Time (seconds) | Current (mA @ 15.3V) | Current (mA @ 12V) | Power (W) |
0 | 185 | 235 | 2.8 |
23 | 263 | 335 | 4.0 |
30 | 250 | 319 | 3.8 |
Horn
Time (seconds) | Current (mA @ 15.3V) | Current (mA @ 9.2V) | Power (W) |
0 | 40 | 66 | 0.6 |
Car
State | Current (mA @ 15.3V) | Current (mA @ 12V) | Power (W) |
Booting 0 - 23s | Fluctuates ~400 | 510 | 6.1 |
PIC+LED, Voltage Regulators, 2 control circuit boards (no router or camera) | 102 | 130 | 1.6 |
After Booting, not driving (steady-state) | 479 | 611 | 7.3 |
Driving - Accelerating | 5500 | 7012 | 84.1 |
Driving - Constant Speed | 4000 | 5100 | 61.2 |
Note: The driving measurements aren't as accurate because it's hard to read the multiemeter while holding a laptop to drive the car and running down the street after the car. heh. Those numbers are accurate +/- 0.1A.
Steering takes very little power. Once the wiper circuit detects that the wheels have turned, it stops turning them. This happens in < 1 second.
Steering takes very little power. Once the wiper circuit detects that the wheels have turned, it stops turning them. This happens in < 1 second.
Its been my experience that the batteries last for about 1.5hrs under normal use.
Temperature / Over Heating
From the above power measurements we can see that the transistors are driving over 7A @ 12V when accelerating. They're rated for 5A, so they get pretty warm.
The transistor temperature after 25 mins of use indoors (hence lots of accelerating from starting and stopping and not going at max speed very often) was 89°C. The motor was also getting pretty warm at 85°C. When running the car outside, it doesn't seem to get near as hot. Probably because you're driving at a constant speed more often than inside. The transistors are rated for up to 150°C, so I think we're ok. I don't have any information on the motor though.
The transistor temperature after 25 mins of use indoors (hence lots of accelerating from starting and stopping and not going at max speed very often) was 89°C. The motor was also getting pretty warm at 85°C. When running the car outside, it doesn't seem to get near as hot. Probably because you're driving at a constant speed more often than inside. The transistors are rated for up to 150°C, so I think we're ok. I don't have any information on the motor though.
Project Costs
Item | Cost* |
Car | 6 |
2nd control board (from another car) | 6 |
Router | 73 |
Camera | 115 |
Batteries | 67 |
Horn | 3 |
PIC circuit | 6 |
Misc: nuts, bolts, screws, project box, wires, connectors | 20 |
Total | 296 |
* Costs include sales tax and shipping and are rounded to the nearest dollar. Prices are in Canadian dollars.
No comments:
Post a Comment