December 2000

Tuesday 5^th December 2000

Had another email from Karl who it now transpires works for the same company as I do, but in a different part of the country. He is also building a Robot but is a bit more advanced than I am. He gave me some very useful practical tips about building the motor drive circuits, and gave some possible reasons why I keep blowing up the MOSFETs. He also told me about another roboteer John, who is a Robot Wars veteran having built and entered his robot Steel Avenger in several competitions. Like Karl and me, John works for the same company, but again in a different location. He has a very good web site, with a variety of useful information that I will peruse over the next few weeks.

Thursday 7^th December 2000

Two SuperWinch motors arrived today. They looked much more substantial than the ones I had previously bought from Display Electronics. These were 12v versions from SuperWinch's C series motors, and were rated at about 800 watts. The off load current rating was 50 amps and the stall current 500 amps. I think I will have sort out any MOSFET driver problems first before I connect these motors up, or I might risk blowing a few more MOSFETs

A potential problem that immediately struck me when I saw the motors was how I was going to connect the motor shaft to the driving sprocket. There was only a very short stub protruding from the motors, and this was machined so that it would fit into a slot in of the sprocket shaft. There were, however, two bolts that clamped the whole assembly together that could be used to secure a special sprocket assembly to the end of the motor. I will have to put my thinking cap on and do some metal work designing.

Friday 15^th December 2000

I came across an Domain name provider www.easily.co.uk that offered name registration for a period of two years for the sum of £9.99. They also offered web parking space and/or redirection to your existing site for free. This was an offer I couldn't refuse, so I registered the web name www.hassockshog.co.uk and had it redirect to the existing web site on LineOne.

Tuesday 26^th December 2000

I found some time to wire in the new DC DC converter into the motor drive circuit during the evening on Boxing day. Initially the output seemed to be pulled low by something, but after disconnecting the "confidence boosting" LEDs on the MOSFET gates, the voltage rose by 12v. I ran the low powered motors on the bench for several minutes until I noticed the motor wasn't running quite at full speed any more. With the aid of my one and only test instrument (my DVM) I found the converter output was zero again just like it's previous two predecessors. This particular converter was meant to have thermal shutdown and overload protection so I wasn't expecting it to blow. The only reason I can put it down to is that there is not enough decoupling and suppression from the battery source to the driver logic circuit, and the battery source to the power MOSFETs. I have included very little in the way of suppression, but maybe I should really go to town now and suppress everything. It's back to the drawing board again for the circuit.