13 Oct 08 Robot: Initial Hardware Order [rev 2]

Follow on from: http://www.adamsinfo.com/the-robot-hardware-list-wheel-plan-more-ideas/

Discuss in the forums

I’ve given up on trying to source separate motors, motor controllers, encoders and brackets. I’m concerned that my knowledge of mechanics and motors is limited, and that I’m going to spend too much time and money trying to build a movement package myself.

I’ve decided to go for a good motor/controller/encoder package here:

http://www.active-robots.com/products/motorsandwheels/rd01-drive.shtml

Wheel Package

I’ll need two of these, and will have to replace the wheels with the omni directional wheel things I found and linked to in my last post.

I’ll drill the brackets into a thin metal plate, and start building perspex on top. I don’t seem to have paid enough attention to battery/device weight/motor/power and am concerned that the motor and battery combination will not move the device. I don’t yet have an idea of how much it will weigh, but I’ve realized that the perspex is going to have to be as thin and light as possible, and I’m going to have to bear weight in mind with any unnecessary or redundant extra parts.

All I know about ‘torque’ is the higher the better, and gear ratio should be as high as possible in a single gear motor. As I understand, high gear ratio means slower but more powerful movement. Someone please correct me if this understanding is incorrect.

These motors require 12v DC, /530mA which makes a mass consumption of 6W per motor at full load/power. 530mA * 4 motors = 2120mA. The device will not be heavily in motion.

A battery of 4000mAh/11.1V will be sufficient and allowing for up to 1.5A for absolute full operation of the peripherals on top of the motors, this is a total of 3.6A@12V =  43.2W at full usage. . I think this is acceptable and works out at 3.89A@11.1V (with perfect conversion). I think that it’s safe to say on full 4 wheel movement with full peripheral usage, the device will last just over an hour. This is good? In actual fact, the peripherals will not be constantly active, the device will have power save measures, the motors will rarely be in action. 3-5h unreasonable? I’m concerned that constant charge and discharge over 5h of the Li-Ion battery and it won’t last very long. Need ideas on batteries and power.

active-robots.com have useful hardware for this project. I’ve also come across Phidgets http://www.phidgets.com/ which are according to them “products for USB Sensing and Control. They have a good interface board with both analog and digital inputs, and a load of prebuilt plugin hardware modules which is of course perfect. This board is also regular USB and well Linux supported.

I don’t qualify the prebuilt motor setup, and the interface/sensor board as cheating.. This was never about robotics. I’ve got more great ideas on software such as voice activated commands, and text to speech back. See this for another great idea: http://shop.david-laserscanner.com/product_info.php/info/p75_Red-Line-Laser–5mW–with-Wall-Power-Supply.html I’m thinking that the line laser is mounted on a pan/tilt servo but anyway, here’s for big ideas.

I’ve done some research into the I2C bus, and it looks like it’s a pretty simple 2 wire protocol. I’d rather use the I2C bus than USB for sensor and hardware comms as that is what I2C is for.

I’d like to order the main board, 1 IO board, some sensors (an IR one and a light one will be sufficient to get working with), that motor/wheel setup, and 4 of the small omnidirectional wheels. I’m not going to get anything else until I have successfully installed and customized Linux on the board, discovered and worked with the board for some time, and got the IO board and motors working. Once that’s done, I’ll need to get some housing for the device, and get a battery/charger setup. From then I will build the device upwards, from the board, IO cards, and few sensors, to the cams, mic, etc on the head.

Initial Hardware Order:
ALIX Main Board: http://linitx.com/viewproduct.php?prodid=11820
Atheros AR5212abg miniPCI wifi [Have already got]
Some 512MB CF cards [have already got]
picoLCD 4×20 http://www.mini-box.com/PicoLCD-4X20-Sideshow

2x motor/motor controller/brackets http://www.active-robots.com/products/motorsandwheels/rd01-drive.shtml
wheels http://www.superdroidrobots.com/shop/item.asp?itemid=27&catid=16
Phidgets 8 analog in/8 digital in/8 digital out USB interface card http://www.phidgets.com/products.php?product_id=1018
Unless anyone can assist me, I will need to ask Phidgets some questions before I order the sensors:
2x 10-70cm IR distance sensor: Will one of these sensors and their beams conflict with nearby sensors? i.e. can I not use IR as my distance sensor method around the device?

http://www.phidgets.com/products.php?product_id=1102 This is a 5mm IR, will this be ok in conjunction with the two above to cover the 10cm to 5mm distances?

1x Light Sensor http://www.phidgets.com/products.php?product_id=1127
Sensor Cables http://www.phidgets.com/products.php?product_id=3002
Misc cable single wire cable.

Look ok for an order list?

Oh for cooling later on, I’m planning to have a fan sucking air in from the base, and another pushing air out at the top of the device, heat rising and all that. I’ll have to try and make the casing around it as hole proof as possible for this to be effective. Any better ideas?

Discuss in the forums

Tags: alix, APNIC, atheros, CF, embedded, i2c, Linux robot, motor, picolcd, Robot

Reader's Comments

1. Adam Palmer | 13 Oct 2008 10:31 pm

   I need to also contact linitx and ask them where the I2C bus is on the board. It seems the board just provides an LPC header, and so I’ll need a compatible expansion card with an I2C bus and anything else of interest that the expansion can also offer.

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