It's not necessarily suspicious, but the airport staff are trained to look more closely at anything unusual. As you may suspect, a big device with wires and batteries will likely garner some additional attention.
The best thing to do is to be prepared. Make sure that you've checked the airline's list of prohibited items (the one with guns, grenades are obvious, but there's also the batteries etc). Make sure none of the prohibited items are carry-on, so that you'll be checking everything in the hold. That gets rid of half their concern, if you won't have access to it during the flight.
Then, bring documentation. Have a print out of the competition details, hopefully your entry form, details of where you built it, a letter perhaps from your company/university where it was built detailing the purpose.
Also include print outs of your accommodation, and any correspondence you have with organisers of the competition.
When it comes to the security check, what the staff are generally doing is looking for answers to questions that your robot will raise. Is it a bomb or benign? Is it dangerous? What are all those spare parts? If you can answer those easily and clearly, with documentation, then they've done their job and will be at ease with it.
Every day people travel with equipment, devices, and more and more these days with wires, batteries and cables, so they're becoming more knowledgeable and understanding.
One last tip - get there early, and check in and go through security as early as possible. This reduces your chance of encountering a stressed agent (at departure, anyway) and also in the event of extra questioning, or inspection of your device by an expert, reduces the risk of you missing your flight.