My current project: a Large rover! I have found a cheap dis-used electric wheelchair on eBay, removed the "chair" and all of the electronics, created a power distribution system behind the battery pack based around an arduino Uno, two 8 channel relay modules, and two 15A step-down converters for 12v and 5v.
On top I have replaced the chair with a aluminum frame where most of the 'higher' level electronics reside, currently this comprises of an Arduino due, a raspberry pi, 1TB Hard drive, a pair of 25A motor controllers, a uBlox GPS, a network hub, WiFi bridge and a USB Hub.
The plan is to use the Arduino DUE as the brains for the motor drive, it's managing the navigation and drive of both motors. I plan to base the navigation around the 9DOF sensor pack I have added as a primary source of information, corrected by GPS & barometer for altitude. I have a set of SR04 ultrasonic sensors that will provide a 'distance' measurement for navigation as well.
Once the basics have been sorted (ie navigation & drive) I have plans to interface the rover into a Kinect sensor; I have begun work on this already, however I require a fairly powerful computer for the image processing if I want to do 3D point cloud, navigation (damn hard), and person recognition as security for commands (nearly done).
For now, I just thought that I would share...
Comments
hmmm, you're not drawing power of half the pack I hope? this will unbalance your pack quite severely! there will always be the cells that form 24v that will drop faster than the rest, leaving perhaps 20-30% charge in the other side while the 24v supply side will be flat. I can't even find decent buck converters that will tolerate 50-60v, I'm not sure how you will do this... beware of using the 'LM' series of regulators, they work by burning off the excess voltage. in the configuration that you have shown, it will dissipate 20W worth of heat (5A @ 4v nom, 24v-4v = 20v) this is actually an awful lot of heat, and an amazing waste of power! I suggest looking at buck converters, they basically take the wattage of the circuit + their running watts (usually 1 or 2) to run, they are much more efficient because of this.
I haven't done a lot of research on 48v stuff, but a cursory look tells me that it is going to be very difficult for you to find suitably rated gear to fulfill your power requirements. you might be better off running the system on a 24v pack or 36v perhaps?
BTW it is almost all 6061 Aluminum, only the side forks are rectangular tube SS (and I did polish).
Hi Jesse here is current "loose" block diagram:
Very cool! I'm sure the folks over on the diyrovers google group would love to hear about these wheelchair robots. Most of ours on that group have scratch built controllers/algorithms on top of RC cars but the "big" wheelchair builds are really cool.
mmmm I love working with stainless steel! it's great stuff to weld with a tig, and usually comes out quite nicely!! should get yourself a dremel and polish the whole frame up then clear coat it, it'd look awesome!!
Aluminium is good to work with as well, I would consider using it for parts of your frame; your acceleration and stopping is very much limited by the overall weight, I wouldn't add to it unless need be. Inertia is a bitch. Those wheels may absorb a lot of energy moving the robot around slowly as well, they are designed to move fairly quickly for a constant amount of time, when standing still with power applied (ie balancing, slow maneuvering) they may collect an awful lot of heat that might need to dissipated somehow (a heatsink or something similar).
mind your power management too; 48V is a lot of power, consider everything you do in watts! 1A @ 48V is twice the power of 1A @ 24V, etc. this level of energy doesn't give a lot of opportunity for second chances; breakers and/or PTC fuses at the battery level will go a long way towards staving off disaster in a fall, or in normal working conditions.
I'm considering the use of a UDoo for the image processing on the Kinect, but until I get my hands on one I am not sure if it really will be fast enough. I am waiting for a quad core version. My robot however does have provisions to mount a reasonable sized PC Motherboard in it; and a friend has given me a sony laptop that might be able to be used, so processing power shouldn't be an issue.
TCIII: I have actually started work some months ago on the Kinect stuff; I've got a few spare sensors sitting around at the moment, one of them already has a dead motor to drive it; I plan on building a gimbal to control the direction of the camera, I was considering if I should use something to look after the vertical part in the gimbal as well instead of relying on that fragile little motor. but I am undecided at the moment... and that's ok because I am waiting for a 12 wire slip ring that I will build the gimbal on...
Hi Jesse,
I have the two 500 watt wheels, the reversible and regen Kelley controllers, 48 volt DC to 12 and 5 volt DC converter, the APM and a Kinect plus a Laptop interfaced to MS robotics studio.
The 6061 frame metal is cut with SS side forks installed.
Am waiting on some "more" SS hardware from Bolt Depot.
I have an initial wiring setup for the APM to run the Kelley controllers throttles, reverse and regen as well as 8 inputs from hall devices in wheels to read wheel position (3 in each wheel) one added external
I spent a lot of time looking for a sufficient microcontroller with adequate I/O to handle the bicycle and in the end came back to the APM and now the Pixhawk.
Eventually the Pixhawk is going to be the superior solution because they are also working on a separate CAN interfaced distributed processing IO controller for it that will be perfect for "arms" and other peripherals.
Eventually I may be able to replace the laptop with an SBPC, but initially, it will make development a lot easier and my chassis has enough room for it.
All up it should weigh between 140 and 160 pounds and will probably have a top speed approaching 30 mph (which I will not be using).
I would have preferred more torque and less speed, but bicycle wheels are bicycle wheels.
Ive been wanting to build this style and size of hanging pendulum robot for 30 years and it has finally become practical (I hope) to do so.
Gary, that should be really interesting when you get it up and running? how far along are you?
Machina; I don't actually have a diagram of the power system; I'm a "figure it out as you go" kinda guy... I can explain it tho? I have four brass rails, 0v, 24v (B+), 5v, and 12v. 24v is always live. 5v is fed from the 5v 15A converter via a relay. to power the unit on I use a momentary toggle to short the switch contacts of the relay, the arduino UNO takes over holding the relay after it boots. this is the lowest power mode running the hub, the unu, relay, Pi, hard drive, and DUE. from here the UNO can start the 12v rail; this will supply things like lights, the Kinect, laptops etc. the rest of the relays provide a means to toggle the WiFi bridge, arming the motors, releasing the brakes, turning lower navigation sensors on and off (these are just optical proximity at the moment) upper nav sensors (more optical proximity, plus some sonar sensors) and anything else that doesn't need to be constantly powered.
I hope this is enough info, if you are designing something of a similar caliber you are always welcome to message me and I can assist.
Jesse,
Kindly post more details about the power distribution system. A diagram would be most helpful. Thanks.
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Regards
Gary ,
Interesting Bicycle . good luck
Hi Jesse,
I too am building a Big Bot.
Mine uses 2 26" brushless bicycle wheels in a hanging pendulum format.
It needs it's 92 pounds of batteries to keep it upright.
I am also going to be incorporating a Kinect,but I am using a laptop in the Bot itself and that also makes it easy to use Microsofts Robot Development System software.
Initially I will be using an APM for the IO control but will be switching to a Pixhawk when I can afford it.
I have most of the components (except the batteries) and am cutting and assembling the Chassis now.
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