30th June 2001 The 17rpm motors have arrived and UDO 4 is back on its wheels, complete and ready for a new trial run. The motor failures on the receivers posed a serious problem because the CPU print was situated too close to the receiver. To overcome this, I have placed the receivers to the front and the CPU print to the back so that the feed wires to the drive motors have a minimum length. The receivers are now causing more problems than they did before because they were taken from UDO 3 and have become very dirty due to the grass flying about. Before long, I will have to build new ones because the receiving sensitivity of both is going to differ considerably. For the time being, I will solve this by screening the most sensitive one to some extent with aluminium foil. Now that UDO 4 has been fully sealed, I'm not going to let this happen again with reference to the new receivers. In addition, I placed the reception aerials a bit further back just in front of the wheels. I have done so because UDO 3 while following the transmission wire rounded the corner a little too early when approaching a square outside bend. But this solution came to nothing because it was difficult for the software to determine where the UDO's front or rear side was. The aerials have therefore been mounted back again at the front at an angle of 45 degrees. The mowing disk, too, keeps causing problems. I have to put too much energy in it to obtain a satisfactory mowing result (one motor even burnt out). Now I am devising something with a disk, underneath which the cutting blades are situated approximately 5 cm lower by using distance bushes. However, I only hope that the disk will not get out of balance too much. The 17rpm motors are performing very well. Should UDO 4 become a success, I'm going to order the 8rpm motors. The mower is still driving a trifle too fast. But now UDO 4 is mowing satisfactorily with UDO 3's smaller mowing disk mounted, and the bumper with integrated air pressure sensor has worked out really well. Next, we are going to conduct a 20-hour endurance test and then we are going to work on the charging station plus some software.
20th July 2001 UDO has stopped after having mowed for 15 hours. One of the driving motors has broken down. On closer examination, it turned out that the reduction gears had worn out completely. It also came to light at this stage that the supplier had exaggerated the specifications of these motors by a factor 10. Currently, I have not been able to find any affordable motors yet which meet the requirements. But there's Jan again, who remarks: ``So far, we have made almost everything ourselves. Why don't we build our own reducing gear unit?'' Well, in AutoCad I have been experimenting with gear wheels but that became too complex. However, a toothed-belt drive seems to be the best choice because it relieves the motors from the jolts which occur when stopping and when changing direction of rotation. One thing and another has resulted in a compromise, namely a gear motor with a belt transmission. We are going to mill it out on Jan's machine.
15th August 2001 A real success this drive unit is. According to calculations, it is capable of carrying 80 kg and the unit loads the gear motor only with half the capacity. In addition, it weighs less than 200 grams without motor. UDO re-assembled, and there we go again for a new run. The cutting blade still constitutes a problem. It requires too much energy to let the 280mm long blade rotate. This turns out to be caused by the fact that the freshly mown grass is thrown against the blunt sides of the blade in the centre of the disk. It also turns out that the lighter the mowing disk the better the results. At first I thought that if the disk has a high mass, it would keep turning when the going gets tough for a moment. Nothing turned out to be further from the truth, for the blade keeps cutting through the grass continuously. The grass that has been mown is constantly being replaced due to the driving action. Therefore, the mower has to cut continuously through a cake of grass. Now I am busy trying out various mowing disks.
20th September 2001 UDO is still performing properly. At present, the mowing disk consists of a 250mm ABS disk which is 4mm thick and has three Stanley knives fitted at an angle of 5 degrees. This disk has been milled off around the blades to a thickness of 0.5 mm to obtain a weight of 100 grams. The underside of this disk is completely smooth so that it meets with little resistance from the mown grass. The mowing motor is still a little too weak. At present, it is approx. 5 watts. I am going to order a 19-watt motor and see whether this is enough. At the same time I am examining the possibility to mount a stationary disk underneath the mowing disk. In so doing, the mowing disk will be subjected to even less resistance from the mown grass.
4th October 2001 So far the mower has been performing trouble-free for some 20 hours. We are well under way to 60 hours. It is planned to construct UDO 4 again in its entirety during the coming winter, the final version for next summer. Meanwhile, however, I keep experimenting with various mowing disks and mowing motors. Just now I realized that only twice have I had to mow the grass by myself and that UDO has done the rest. So, it is really going to work. Now I have also the opportunity to improve the software.
20th January 2002 Have concerned myself far too little with UDO. This is caused by the fact that I have got a new job which demands all my attention. Jan is pushing me on by saying that the grass will be growing again in March. The new design has to undergo two modifications. First, the wire receivers, these are difficult to reproduce without sufficient knowledge of electronics and that is not intended, because everyone should be able to build the mower by him/herself. I have got the idea to use a DCF-77 receiver chip as a receiver. These chips are crystal- controlled and do not have any adjustment points. I have been able to find a chip which fits our purpose nicely, namely the U4224B. This is a DCF receiver chip for 40, 60 and 77.5 kHz. On the outside of the chip are the AGC (Automatic Gain Control) components located. The idea is to use this AGC as a signal intensity output. The second point to be addressed is the energy flowing to the mowing motor. This will be effected by a homebrew PWM controller with two TTL chips and a Power FET.
3rd February 2002 Jan has milled the PCB and the first tests have been conducted. This is going to work, we feel, the recipient is now crystal-controlled at 60 kHz to avoid possible interference caused by the atomic time signal and at the same time I can use the AGC signal to transfer the acknowledgement signal on to the CPU. No doubt, I will have to incorporate an OPAMP because this signal may not be loaded.
23rd February 2002 It didn't work out with the DCF recipient, after all, the load of the AGC controller had to be so low that as much as a greasy finger on the print already caused problems. Therefore, this was useless with a view to people constructing it themselves. I found two people on the Internet who had built an RF recipient for their robot. I have sent them an E-mail asking them how they had dealt with it. One person wrote back that he had converted a dog deterring device by connecting a neon light to the deterring device which activated a photocell. The other person had developed something that was quite similar to my receiver. This answer set me thinking. My receiver wasn't so bad after all, but it needed further development. A bout of hard thinking resulted in the following idea. I'm going to build a PLL receiver by using the NE567. This way, I'll kill two birds with one stone. Firstly, it is not wide- banded anymore so that I will hopefully get less interference from the PWM controllers and secondly, it can be adjusted very well now. First, I'm going to try to connect the receiving coil directly to the chip and if it should turn out that it is too insensitive, I'm going to build a small amplifier for it. To be continued.
17th March 2002 The receiver with the NE567 is working well. Initially, I built it without using a preamplifier, but this was too insensitive. After that, I placed an amplifier with an LM393 downstream of it. Bingo! It is working very well now, with only a small problem to be solved, namely that when the aerial coil is too close to the receiver print, it oscillates. This should be easy to solve, I think, by shielding the print by means of some tin plate. The CPU print has been drawn again and will be tested shortly. The modifications to the print are: Thicker print conductors for the power supply and the motor drive. These were too thin on the old printed circuit board. Now it has been constructed in such a manner that it can be easily mounted in UDO. The leads can now be connected by means of plugs. Some glue electronics have been slightly adjusted; as a result, it is easier to control the LEDs.
And I have developed my first wire transmitter so that the function generator is no longer necessary. This is a crystal-controlled 62.5kHz transmitter with a CD4060. The first tests are promising. The only problem I'm faced with is how to control the power. Currently, this is done by a potentiometer in the power supply, this is not exactly a textbook solution but, what the heck, it works.
I have not been sitting still, as you may have noticed, but neither has the grass. Speedy action is required.
7th April 2002 The receiver, transmitter and the CPU have been put on the print and in a diagram. The prints are being milled at Jan's. The tests with the receiver were satisfactory to good. First, I tried to mount the aerial coil onto the receiver print, but that didn't work at all. The oscillator of the NE567 was picked up by the aerial coil so that it always detected something. Now the receiver print has been 'tinned' and the aerial coils have been placed outside the receivers using a short coax cable.
15th April 2002 The CPU print is working perfectly, there is not even a single fault to be found on the print. Even the new features such as the programming adapter and LED control were operating properly, the first time. The advantage of the integrated programming adapter is that UDO now possesses a real RS232 port. I have used two pins of the 9- pin RS232 port to set the M-Unit to programming and run mode by enabling the M-Unit jumper through a connection in the RS232 plug. Everything has been mounted in the old frame now to subject the new electronic components to a trial run. This went completely wrong. When near the wire, UDO turned into any random direction every time. It took me a day to find out the cause of this phenomenon. But having whiled away some time under the shower, I found the solution (You see, I tend to come up with the best ideas when I'm having a shower. Apart from that, I'm quite all right.) This problem was caused by the fact that the receiving coils were used while being too far from their original 77.5kHz resonance frequency. I used them at 62.5kHz. As a result, the connection coax was just as good an aerial as the coil itself. By connecting an extra capacitor across the coil, I managed to tune it exactly to 62.5 kHz. I did this tuning by connecting the receiving coil to a scope. The aerial transmission wire has been made by connecting a measuring flex to a function generator. By turning the function generator up and down around the 62.5 kHz, the scope shows you exactly where the reception of the aerial is maximal. This was the solution, because UDO is now running even better than last year and it has already logged 8 hours behind the wheels, without as much as a single error. The receivers have now become so sensitive that I will have to modify the mini transmitter a little so that it will send out a weaker signal. The CPU print has now also been provided with a frequency measuring input. I'm going to use this to measure the mowing motor speed by means of an optocoupler on the shaft of the motor. I will use this measurement to let UDO travel more slowly when the speed drops too far. The first tests on the working bench went smoothly. The electronics are now working fine with the advantage compared to last year that the receivers can now be adjusted smoothly according to a fixed adjustment procedure. In addition, they are now insensitive to interference from external sources (CPU and PWM controllers). Now the time has come to design the mechanics. This will not differ very much from the previous version. It is really necessary to have a new frame because the current one has become a holey cheese as a result of all modifications.
5th May 2002 UDO's frame has been milled again by Jan and we have fitted a heavier mowing motor. We also managed to measure the rotational speed of the cutting blade. This has not been done by using an optocoupler but by using a Hall sensor plus a small magnet on the shaft. (``HI-TECH'', nothing is foreign to UDO). Should the speed drop below a set value now, UDO will retreat and then go onto the attack again. The new mowing motor is also a success and fits nicely in the frame without any protruding parts. Jan has milled new wheels as well, first toothed ones but that was too rocky. Now the wheels are entirely round, having staggered teeth. The mini transmitter is working perfectly now and because of the fact that it is crystal-controlled, I do not need to adjust anything to it anymore. UDO has logged another 20 hours of mowing, with one problem still to overcome, namely that the pressure sensor is set slightly too insensitive when bumping sideways against the tree in our garden. I'm not particularly worried about it because this can be adjusted when it is being serviced for the first time. Time to start making new plans. And there are plenty, the most important being that UDO should be able to find its battery charger automatically. At present, I am examining the possibilty to charge UDO using an inductive coupling instead of electric contacts. The advantage of this method is that UDO can remain waterproof and that no poor contact can develop due to oxidation. And a few things just for fun. UDO will be provided with a plexiglass bottom with built-in LEDs. At present, the front has already been fitted with LEDs which represent the sensors. A colleague of mine had a good idea. Dick suggested that UDO should have a state of mind. I'm going to try and achieve this by applying a stress factor within the software which will result - on the basis of the rotational speed of the cutting blade and the number of rotary movements within a set time - in a stress value. So, when the speed is low and UDO has to do a lot of turning within a short time, UDO will change colour from green to red. Don't you worry, we'll bring UDO to life, as long as it doesn't take to drink, because we're only too happy to down a few ourselves.