One problem that I did face was finding a way to connect the USB to the Mega whilst it was installed in the case. Nowhere at home or on the internet could I find a USB B connector that had the correct right angle on it or was short enough to plug-in and still fit in the box.
I even tried cutting up USB B cables and trying to cut the connector out but this ended up very messy and still didn’t fit right. I eventually managed to find a USB B connector at Jaycar that wasn’t listed on their website and once cut down with the Dremel and soldered / glued together this worked. At the other end I managed to get hold of a panel mount USB B socket but had to cut the male connector that was on it off and solder / heatshrink the wires together because there seemed to be no female connector available to solder on the lead coming from the Mega.
All the wires for the LCD and the PS2 controller were soldered to a section of PCB and joined to a row of header pins next to them. This was then flipped upside down so the cables entered from the bottom and plugged in. If anyone knows of a better way of doing this then Id been keen to hear it. The problem is that the Arduino boards all have header sockets on them instead of male pins which means that any of the clip on connectors that you get on IDE HDD cables for example don’t work. I haven’t been able to find any clip on connectors that have male pins, they all seem to be female. I could have soldered the wires directly to a st of header pins but this would have been messy.
Next part was installing the cooling fan for the motor controllers and the connectors to plug into them. The motor controllers used are Pololu A4988 boards, a breakout for the Allegro controllers, rated for 2A per coil. I chose the ones without the onboard voltage regulators as the PSU already gave the correct voltages and so to have them there would have been a waste of space and money. These offer full wave through to 16th wave stepping as well as current limiting. The spec sheet says that for loads above 1A per coil you should use either a heat sink or cooling fan. I opted for both as a backup due to long runtimes and a thus far unconfirmed working current.
Outside of case, top left switch is power, bottom right is reset. DB9 is for connection to PS2 controller with the DB25 going to the Pan etc head.
I managed to grab a new LCD from Surplustronics to replace the old Renesas one, 20×4 White on Blue which should give me enough space to display all the information required. The next step above this would be to get a Graphical LCD although this would just step up the complexity without actually giving much benefit in this application. They’re also a bit more expensive.
A couple of days after doing all this the motor controllers arrived from Robokits in Christchurch. These then got hooked up and mounted on their PCB as per the photo below. The idea was to mount them vertically and try make a channel for the airflow from the cooling fan. Concept great, application not so good.
First problem came when I found that this design covered up rather effectively the pots that control the current limiting, making it rather hard to set up the motors. You can just make out one of the pots on the left hand side of the right hand controller. This photo doesn’t really show it but the white connector blocks a screw driver from getting in there.
The only solution was to try to push the pots around by using a screw driver from above. Whilst troublesome this did work and I figured that I’d only have to do this once during setup. Next problem came however when I went to set up the last controller, regardless of the setting of the pot the motor would only get about 50mA, not the 700mA that it needed.
A check with a multimeter confirmed that the pot was dud. My next problem came when I went to remove the board to swap it out. I had used right angle connectors to attached the controllers to the PCB and unsoldering this proved to be a right pain in the ass. In addition to this I had put drops of superglue on the top edge of the board to back up the “not very sticky” thermal sticky tape. So… not only were the boards near impossible to remove from the PCB but they were also glued together.
I ended up ripping the whole thing apart with side cutters, salvaging the working boards and deciding that a better design was needed.
Peter at Robokits was great and offered to replace the board when I contacted him and explained the issue. Fastway Couriers were not so great and succeeded in losing the board on its return trip to Christchurch. Eightish weeks later, many many calls to CS and my claim for lost goods is still being processed. JT’s Consumer Advice. STAY AWAY FROM FASTWAY.
Part 4 up next