Show All ItemsLike many people, I have wanted to use the base of a power wheelchair for remote control projects. However, proper motor controllers are expensive, and I thought there had to be a cheaper solution. I originally bought brushed ESCs (electronic speed controllers) that are omnidirectional but fit with my goal of making it remote controllable. The ESCs were great for proof of concept, helped me size batteries but couldn't run at 24V. I have a previous instructable detailing my journey of learning how to work with RC and Arduino. Thus, I will not cover the programming side extensively and will instead focus more on the hardware side. RC Control and Arduino: A Complete WorksMy prototype above cost $120 excluding RC gear.Power Wheelchair $Free.99Batteries $50Motor Controller Electronics $24 for both motors SCORE!Arduino Uno $35Wire $10 and have plenty of extraStep 1: The BasicsShow All ItemsI'm working with brushed DC motors which makes things rather simple compared to brushless.
The few basic parts are as follows.Power Source:I chose two sealed lead acid batteries with 10Ah of capacity that should get me 20-30 minutes of use.Fuse/Holder:Always protect your project and a good rule of thumb is to use 125% of your stall current. I floored my motors while sitting on robot on carpet and measured the current with a power analyzer. Then used the next automotive fuse up from that measured value.High Speed Switch:A device that can ideally switch in the nanoseconds. I.E. Mosfets, Solid State Relays.Low Speed Switch:Device that can switch in the tens of milliseconds. I.E. Standard RelaysFlyback Protection:Once you stop supplying power to the motors but they are still moving they turn into generators. You have to bypass or sink this power or you will let the magic smoke out! Also known as freewheeling, snubbing, suppression.« PreviousNext »View All Steps DownloadUsed Mobility Scooter Power Wheelchair Pride Jazzy Select 3 miles Or Less MotorHigh Quality Lithium Battery Packs for EVs
Torque (in N*m) = 9.55 * Power (in watts) / Speed (in rpm) 1N*m = 141.61 oz*in = 8.85 lb*in = 10,200.0 g*cm, 1.0 hp = 745.7 watts 1.0 in = 2.54 cm, 1.0 kg = 2.205 lb = 35.27 oz, 1.0 mile = 1.61 Km, Tc=(Tf-32)*5/9 20'/ft Container Volume: 33cbm/1170cft (internal: 5.9m x 2.35m x 2.39m) 40'/ft Container Volume: 67cbm/2385cft (internal: 12.0m x 2.35 x 2.39m) Air Shipping Volume to Weight Conversion Formula: [L(cm) * W(cm) * H(cm)]/6000 => Kgs More Formulas and Equations About DC Motors... This document gives a detailed description of the wheelchair controllerYou don't need to read this unless you are an engineer, and want to customize the design. The electronics are comprised of two electronic boards: The joystick motor controller board, and the joystick board. The motor controller board receives signals from the joystick board, and controls the motors. The joystick signal is a voltage level from 0 to 3.3V, with 1.65V being the rest state of the
The motor controller is comprised of 2 MOSFET H-bridges, one for each motor, a Texas Instruments MSP430G2295 processor, several status LEDs, a 3.3V voltage regulator, a reverse polarity protection circuit, a 15 amp mini blade automotive fuse, a USB bridge, and a power on MOSFET switch. We used the MSP430G2295 because it is cheap, has a C-friendly architecture, is low power, has a free C compiler and affordable development tools, is firmware upgradeable via it's UART port, and simply we have a lot of experience with it. The processor receives analog inputs from the joystick, and converts these values into digital values, which are in turn converted intoThe polar value is then used to update the direction and speed of the motors. The motor speed is controlled by 2KHz PWM signals. The motors only use a couple of amps each so the MOSFETS only get slightly warm, at this low PWM The reverse polarity circuit consists of a MOSFET and zener diode which
block the current if the battery inputs are reversed. The gate of the power-on MOSFET must be tied low through the JOYSTICK switch for it to pass power to the circuit. We had considered running the battery input in series with the power switch, but we would have had to use heavy gauge wire, and run this up to the power switch on the joystick enclosure which would have made cable routing more difficult, and in addition this high current line would have induced noise on theThe power-on MOSFET on the board needs only a low power control signal, and so we could allocate one of the Ethernet cable wires for this function. The joystick board mates to the joystick, has an Ethernet modular connector and a switch connector. We created this board to standardize the wiring of the joystick, as we realized that there were just too many ways that an end user could connect it up incorrectly. The joystick board has fault detection.
that if one of the control wires from the joystick board broke, the wheelchair would interpret the situation as the joystick being pressed to an extreme and send the wheelchair out of control. this potential situation, we added resistors to each of the positive and negative sides of each of the two potentiometers in the joystick. These resistors offset the minimum and and maximum voltagesWithout the resistors, the minimum and maximum voltages for the X and Y joystick inputs are 0, and 3.3VWith the resistors the minimum and maximum voltages are .15V, and 3.15V respectively. resistors, we know that if the controller receives an input voltage that is below 0.15V or above 3.15V there is a potential problem and we can disable the motors, and indicate an error condition. USB bridge is a Chinese Prolific brand USB PBL2303 chip. This chip was chosen because it cheap and has decent driverThe only problem we encountered is that some vendors are